Sec.

B36.1      General.

B36.3      Perceived noise level.

B36.5      Correction for spectral irregularities.

B36.7      Maximum tone corrected perceived noise level.

B36.9      Duration correction.

B36.11      Effective perceived noise level.

B36.13      Mathematical formulation of noy tables.

Section B36.1 General. The procedures in this appendix must be used to determine the noise evaluation quantity designated as effective perceived noise level, EPNL, under §§36.103 and 36.803. These procedures, which use the physical properties of noise measured as prescribed by appendix A of this part, consist of the following:

(a) The 24 one-third octave bands of sound pressure level are converted to perceived noisiness by means of a noy table. The noy values are combined and then converted to instantaneous perceived noise levels, PNL(k).

(b) A tone correction factor, C(k), is calculated for each spectrum to account for the subjective response to the presence of the maximum tone.

(c) The tone correction factor is added to the perceived noise level to obtain tone corrected perceived noise levels, PNLT(k), at each one-half second increment of time. The instantaneous values of tone corrected perceived noise level are noted with respect to time and the maximum value, PNLTM, is determined.

PNLT(k)=PNL(k)+C(k)

(d) A duration correction factor, D, is computed by integration under the curve of tone corrected perceived noise level versus time.

(e) Effective perceived noise level, EPNL, is determined by the algebraic sum of the maximum tone corrected perceived noise level and the duration correction factor.

EPNL=PNLTM+D

Section B36.3 Perceived noise level. Instantaneous perceived noise levels, PNL(k), must be calculated from instantaneous one-third octave band sound pressure levels, SPL(i,k), as follows:

(a) Step 1. Convert each one-third octave band SPL(i,k), from 50 to 10,000 Hz, to perceived noisiness, n(i,k), by reference to Table B1, or to the mathematical formulation of the noy table given in §B36.13 of this appendix.

(b) Step 2. Combine the perceived noisiness values, n(i,k), found in step 1 by the following formula:

N(k)=n(k)+0.15 [[Σ24i−1

n(i,k)]−n (k)]=0.85

n(K)+0.15Σ24i−1n(i,k)

where n(k) is the largest of the 24 values of n(i,k) and N(k) is the total perceived noisiness.

(c) Step 3. Convert the total perceived noisiness, N(k), into perceived noise level, PNL(k), by the following formula:

PNL(k)=40.0+33.22 log N(k)

which is plotted in Figure B1. PNL(k) may also be obtained by choosing N(k) in the 1,000 Hz column of Table B1 and then reading the corresponding value of SPL(i,k) which, at 1,000 Hz, equals PNL(k).

View or Download PDF

                                                           Table B1--Perceived Noisiness (NOYs) as a Function of Sound Pressure Level
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                           \1/3\ Octave Band Center Frequencies in Hz (c/s)
 SPL -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
       50    63     80      100     125     160     200     250     315     400     500     630     800    1000    1250    1600    2000    2500    3150    4000    5000    6300    8000    10000
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
   4  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.10  ......    0.10  ......  ......  ......
                                                                                                                                                                                          1  1
1  5  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.10    0.11    0.10  ......  ......  ......  ......
   6  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.11    0.12    0.11  ......  ......  ......  ......
   7  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.13    0.14    0.13    0.10  ......  ......  ......
   8  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.14    0.16    0.14    0.11  ......  ......  ......
   9  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.10    0.16    0.17    0.16    0.14  ......  ......  ......
 
  10  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.11    0.17    0.19    0.18    0.16    0.10  ......  ......
  11  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.13    0.19    0.22    0.21    0.18    0.12  ......  ......
  12  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.10    0.14    0.22    0.24    0.24    0.21    0.14  ......  ......
  12  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.11    0.16    0.24    0.27    0.27    0.24    0.16  ......  ......
  14  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.13    0.18    0.27    0.30    0.30    0.27    0.19  ......  ......
 
  15  ....  ....  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......    0.10    0.14    0.21    0.30    0.33    0.33    0.30    0.22  ......  ......
  16  ....  ....  ......  ......  ......  ......  ......  ......  ......    0.10    0.10    0.10    0.10    0.10    0.11    0.16    0.24    0.33    0.35    0.35    0.33    0.26  ......  ......
  17  ....  ....  ......  ......  ......  ......  ......  ......  ......    0.11    0.11    0.11    0.11    0.11    0.13    0.18    0.27    0.35    0.38    0.38    0.35    0.30    0.10  ......
  18  ....  ....  ......  ......  ......  ......  ......  ......    0.10    0.13    0.13    0.13    0.13    0.13    0.15    0.21    0.30    0.38    0.41    0.41    0.38    0.33    0.12  ......
  19  ....  ....  ......  ......  ......  ......  ......  ......    0.11    0.14    0.14    0.14    0.14    0.14    0.17    0.24    0.33    0.41    0.45    0.45    0.41    0.36    0.14  ......
 
  20  ....  ....  ......  ......  ......  ......  ......  ......    0.13    0.16    0.16    0.16    0.16    0.16    0.20    0.27    0.36    0.45    0.49    0.49    0.45    0.39    0.17  ......
  21  ....  ....  ......  ......  ......  ......  ......    0.10    0.14    0.18    0.18    0.18    0.18    0.18    0.23    0.30    0.39    0.49    0.53    0.53    0.46    0.42    0.21    0.10
  22  ....  ....  ......  ......  ......  ......  ......    0.11    0.16    0.21    0.21    0.21    0.21    0.21    0.26    0.33    0.42    0.53    0.57    0.57    0.53    0.46    0.25    0.11
  23  ....  ....  ......  ......  ......  ......  ......    0.13    0.18    0.24    0.24    0.24    0.24    0.24    0.30    0.36    0.46    0.57    0.62    0.62    0.57    0.50    0.30    0.13
  24  ....  ....  ......  ......  ......  ......    0.10    0.14    0.21    0.27    0.27    0.27    0.27    0.27    0.33    0.40    0.50    0.62    0.67    0.67    0.62    0.55    0.33    0.15
 
  25  ....  ....  ......  ......  ......  ......    0.11    0.16    0.24    0.30    0.30    0.30    0.30    0.30    0.35    0.43    0.55    0.67    0.73    0.73    0.67    0.60    0.36    0.17
  26  ....  ....  ......  ......  ......  ......    0.13    0.18    0.27    0.33    0.33    0.33    0.33    0.33    0.38    0.48    0.60    0.73    0.79    0.79    0.73    0.65    0.39    0.20
  27  ....  ....  ......  ......  ......    0.10    0.14    0.21    0.30    0.35    0.35    0.35    0.35    0.35    0.41    0.52    0.65    0.79    0.85    0.85    0.79    0.71    0.42    0.23
  28  ....  ....  ......  ......  ......    0.11    0.16    0.24    0.33    0.38    0.38    0.38    0.38    0.38    0.45    0.57    0.71    0.85    0.92    0.92    0.85    0.77    0.46    0.26
  29  ....  ....  ......  ......  ......    0.13    0.18    0.27    0.35    0.41    0.41    0.41    0.41    0.41    0.49    0.63    0.77    0.92    1.00    1.00    0.92    0.84    0.50    0.30
 
  30  ....  ....  ......  ......    0.10    0.14    0.21    0.30    0.38    0.45    0.45    0.45    0.45    0.45    0.53    0.69    0.84    1.00    1.07    1.07    1.00    0.92    0.55    0.33
  31  ....  ....  ......  ......    0.11    0.16    0.24    0.33    0.41    0.49    0.49    0.49    0.49    0.49    0.57    0.76    0.92    1.07    1.15    1.15    1.07    1.00    0.60    0.37
  32  ....  ....  ......  ......    0.13    0.18    0.27    0.36    0.45    0.53    0.53    0.53    0.53    0.53    0.62    0.83    1.00    1.15    1.23    1.23    1.15    1.07    0.65    0.41
  33  ....  ....  ......  ......    0.14    0.21    0.30    0.39    0.49    0.57    0.57    0.57    0.57    0.57    0.67    0.91    1.07    1.23    1.32    1.32    1.23    1.15    0.71    0.45
  34  ....  ....  ......    0.10    0.16    0.24    0.33    0.42    0.53    0.62    0.62    0.62    0.62    0.62    0.73    1.00    1.15    1.32    1.41    1.41    1.32    1.23    0.77    0.50
 
  35  ....  ....  ......    0.11    0.18    0.27    0.36    0.46    0.57    0.67    0.67    0.67    0.67    0.67    0.79    1.07    1.23    1.41    1.51    1.51    1.41    1.32    0.84    0.55
  36  ....  ....  ......    0.13    0.21    0.30    0.40    0.50    0.62    0.73    0.73    0.73    0.73    0.73    0.85    1.15    1.32    1.51    1.62    1.62    1.51    1.41    0.92    0.61
  37  ....  ....  ......    0.15    0.24    0.33    0.43    0.55    0.67    0.79    0.79    0.79    0.79    0.79    0.92    1.23    1.41    1.62    1.74    1.74    1.62    1.51    1.00    0.67
  38  ....  ....  ......    0.17    0.27    0.37    0.48    0.60    0.73    0.85    0.85    0.85    0.85    0.85    1.00    1.32    1.51    1.74    1.86    1.86    1.74    1.62    1.10    0.74
  39  ....  ....    0.10    0.20    0.30    0.41    0.52    0.65    0.79    0.92    0.92    0.92    0.92    0.92    1.07    1.41    1.62    1.86    1.99    1.99    1.86    1.74    1.21    0.82
 
  40  ....  ....    0.12    0.23    0.33    0.45    0.57    0.71    0.85    1.00    1.00    1.00    1.00    1.00    1.15    1.51    1.74    1.99    2.14    2.14    1.99    1.86    1.34    0.90
  41  ....  ....    0.14    0.26    0.37    0.50    0.63    0.77    0.92    1.07    1.07    1.07    1.07    1.07    1.23    1.62    1.86    2.14    2.29    2.29    2.14    1.99    1.48    1.00
  42  ....  ....    0.16    0.30    0.41    0.55    0.69    0.84    1.00    1.15    1.15    1.15    1.15    1.15    1.32    1.74    1.99    2.29    2.45    2.45    2.29    2.14    1.63    1.10
  43  ....  ....    0.19    0.33    0.45    0.61    0.76    0.92    1.07    1.23    1.23    1.23    1.23    1.23    1.41    1.86    2.14    2.45    2.63    2.63    2.45    2.29    1.79    1.21
  44  ....  0.10    0.22    0.37    0.50    0.67    0.83    1.00    1.15    1.32    1.32    1.32    1.32    1.32    1.52    1.99    2.29    2.63    2.81    2.81    2.63    2.45    1.99    1.34
 
  45  ....  0.12    0.26    0.42    0.55    0.74    0.91    1.08    1.24    1.41    1.41    1.41    1.41    1.41    1.62    2.14    2.45    2.81    3.02    3.02    2.81    2.63    2.14    1.48
  46  ....  0.14    0.30    0.46    0.61    0.82    1.00    1.16    1.33    1.52    1.52    1.52    1.52    1.52    1.74    2.29    2.63    3.02    3.23    3.23    3.02    2.81    2.29    1.63
  47  ....  0.16    0.34    0.52    0.67    0.90    1.08    1.25    1.42    1.62    1.62    1.62    1.62    1.62    1.87    2.45    2.81    3.23    3.46    3.46    3.23    3.02    2.45    1.79
  48  ....  0.19    0.38    0.58    0.74    1.00    1.17    1.34    1.53    1.74    1.74    1.74    1.74    1.74    2.00    2.63    3.02    3.46    3.71    3.71    3.46    3.23    2.63    1.98
  49  0.10  0.22    0.43    0.65    0.82    1.08    1.26    1.45    1.64    1.87    1.87    1.87    1.87    1.87    2.14    2.81    3.23    3.71    3.97    3.97    3.71    3.46    2.81    2.18
 
  50  0.12  0.26    0.49    0.72    0.90    1.17    1.36    1.56    1.76    2.00    2.00    2.00    2.00    2.00    2.30    3.02    3.46    3.97    4.26    4.26    3.97    3.71    3.02    2.40
  51  0.14  0.30    0.55    0.80    1.00    1.26    1.47    1.68    1.89    2.14    2.14    2.14    2.14    2.14    2.46    3.23    3.71    4.26    4.56    4.56    4.26    3.97    3.23    2.63
  52  0.17  0.34    0.62    0.90    1.08    1.36    1.58    1.80    2.03    2.30    2.30    2.30    2.30    2.30    2.64    3.46    3.97    4.56    4.89    4.89    4.56    4.26    3.46    2.81
  53  0.21  0.39    0.70    1.00    1.18    1.47    1.71    1.94    2.17    2.46    2.46    2.46    2.46    2.46    2.83    3.71    4.26    4.69    5.24    5.24    4.89    4.56    3.71    3.02
  54  0.25  0.45    0.79    1.09    1.28    1.50    1.85    2.09    2.33    2.64    2.64    2.64    2.64    2.64    3.03    3.97    4.56    5.24    5.61    5.61    5.24    4.89    3.97    3.23
 
  55  0.30  0.51    0.89    1.18    1.39    1.71    2.00    2.25    2.50    2.83    2.83    2.83    2.83    2.83    3.25    4.26    4.89    5.61    6.01    6.01    5.61    5.24    4.26    3.46
  56  0.34  0.59    1.00    1.29    1.50    1.85    2.15    2.42    2.69    3.03    3.03    3.03    3.03    3.03    3.48    4.56    5.24    6.01    6.44    6.44    6.01    5.61    4.56    3.71
  57  0.39  0.67    1.09    1.40    1.63    2.00    2.33    2.61    2.88    3.25    3.25    3.25    3.25    3.25    3.73    4.89    5.61    6.44    6.90    6.90    6.44    6.01    4.89    3.97
  58  0.45  0.77    1.18    1.53    1.77    2.15    2.51    2.81    3.10    3.48    3.48    3.48    3.48    3.48    4.00    5.24    6.01    6.90    7.39    7.39    6.90    6.44    5.24    4.26
  59  0.51  0.87    1.29    1.66    1.92    2.33    2.71    3.03    3.32    3.73    3.73    3.73    3.73    3.73    4.29    5.61    6.44    7.39    7.92    7.92    7.39    6.90    5.61    4.56
 
  60  0.59  1.00    1.40    1.81    2.08    2.51    2.93    3.26    3.57    4.00    4.00    4.00    4.00    4.00    4.59    6.01    6.90    7.92    8.49    8.49    7.92    7.39    6.01    4.89
  61  0.67  1.10    1.53    1.97    2.26    2.71    3.16    3.51    3.83    4.29    4.29    4.29    4.29    4.29    4.92    6.44    7.39    8.49    9.09    9.09    8.49    7.92    6.44    5.24
  62  0.77  1.21    1.66    2.15    2.45    2.93    3.41    3.79    4.11    4.59    4.59    4.59    4.59    4.59    5.28    6.90    7.92    9.09    9.74    9.74    9.09    8.49    6.90    5.61
  63  0.87  1.32    1.81    2.34    2.65    3.16    3.69    4.06    4.41    4.92    4.92    4.92    4.92    4.92    5.66    7.39    8.49    9.74    10.4    10.4    9.74    9.09    7.39    6.01
  64  1.00  1.45    1.97    2.54    2.88    3.41    3.98    4.39    4.73    5.28    5.28    5.28    5.28    5.28    6.06    7.52    9.09    10.4    11.2    11.2    10.4    9.74    7.92    6.44
 
  65  1.11  1.60    2.15    2.77    3.12    3.69    4.30    4.71    5.08    5.66    5.66    5.66    5.66    5.66    6.50    8.49    9.74    11.2    12.0    12.0    11.2    10.4    8.49    6.90
  66  1.22  1.75    2.34    3.01    3.39    3.99    4.64    5.07    5.45    6.06    6.06    6.06    6.06    6.06    6.96    9.09    10.4    12.0    12.8    12.8    12.0    11.2    9.09    7.39
  67  1.35  1.92    2.54    3.28    3.68    4.30    5.01    5.46    5.85    6.50    6.50    6.50    6.50    6.50    7.46    9.74    11.2    12.8    13.8    13.8    12.8    12.0    9.74    7.92
  68  1.49  2.11    2.77    3.57    3.99    4.64    5.41    5.88    6.27    6.96    6.96    6.96    6.96    6.96    8.00    10.4    12.0    13.8    14.7    14.7    13.8    12.8    10.4    8.49
  69  1.65  2.32    3.01    3.80    4.33    5.01    5.84    6.33    6.73    7.46    7.46    7.46    7.46    7.46    8.57    11.2    12.8    14.7    15.8    15.8    14.7    13.8    11.2    9.09
 
  70  1.82  2.59    3.28    4.23    4.69    5.41    6.31    6.81    7.23    8.00    8.00    8.00    8.00    8.00    9.19    12.0    13.8    15.8    16.9    16.9    15.8    14.7    12.0    9.74
  71  2.02  2.79    3.57    4.60    5.09    5.84    6.81    7.33    7.75    8.57    8.57    8.57    8.57    8.57    9.85    12.8    14.7    16.9    18.1    18.1    16.9    15.8    12.8    10.4
  72  2.23  3.07    3.88    5.01    5.52    6.31    7.36    7.90    8.32    9.19    9.19    9.19    9.19    9.19    10.6    13.8    15.8    18.1    19.4    19.4    18.1    16.9    13.8    11.2
  73  2.46  3.37    4.23    5.45    5.99    6.81    7.94    8.50    8.93    9.85    9.85    9.85    9.85    9.85    11.3    14.7    16.9    19.4    20.8    20.8    19.4    18.1    14.7    12.0
  74  2.72  3.70    4.60    5.94    6.50    7.36    8.57    9.15    9.59    10.6    10.6    10.6    10.6    10.6    12.1    15.8    18.1    20.8    22.3    22.3    20.8    19.4    15.8    12.8
 
  75  3.01  4.06    5.01    6.46    7.05    7.94    9.19    9.85    10.3    11.3    11.3    11.3    11.3    11.3    13.0    16.9    19.4    22.3    23.9    23.9    22.3    20.8    16.9    13.8
  76  3.32  4.46    5.45    7.03    7.65    8.57    9.85    10.6    11.0    12.1    12.1    12.1    12.1    12.1    13.9    18.1    20.8    23.9    25.6    25.6    23.9    22.3    18.1    14.7
  77  3.67  4.89    5.94    7.66    8.29    9.19    10.6    11.3    11.8    13.0    13.0    13.0    13.0    13.0    14.9    19.4    22.3    25.6    27.4    27.4    25.6    23.9    19.4    15.8
  78  4.06  5.37    6.46    8.33    9.00    9.85    11.3    12.1    12.7    13.9    13.9    13.9    13.9    13.9    16.0    20.8    23.9    27.4    29.4    29.4    27.4    25.6    20.8    16.9
  79  4.49  5.90    7.03    9.07    9.76    10.6    12.1    13.0    13.6    14.9    14.9    14.9    14.9    14.9    17.1    22.3    25.6    29L4    31.5    31.5    29.4    27.4    22.3    18.1
 
  80  4.96  6.48    7.66    9.85    10.6    11.3    13.0    13.9    14.6    16.0    16.0    16.0    16.0    16.0    18.4    23.9    27.4    31.5    33.7    33.7    31.5    29.4    23.9    19.4
  81  5.48  7.11    8.33    10.6    11.3    12.1    13.9    14.9    15.7    17.1    17.1    17.1    17.1    17.1    19.7    25.6    29.4    33.7    36.1    36.1    33.7    31.5    25.6    20.8
  82  6.06  7.81    9.07    11.3    12.1    13.0    14.9    16.0    16.9    18.4    18.4    18.4    18.4    18.4    21.1    27.4    31.5    36.1    38.7    38.7    36.1    33.7    27.4    22.3
  83  6.70  8.57    9.87    12.1    13.0    13.9    16.0    17.1    18.1    19.7    19.7    19.7    19.7    19.7    22.6    29.4    33.7    38.7    41.5    41.5    38.7    36.1    29.4    23.9
  84  7.41  9.41    10.7    13.0    13.9    14.9    17.1    18.4    19.4    21.1    21.1    21.1    21.1    21.1    24.3    31.5    36.1    41.5    44.4    44.4    41.5    38.7    31.5    25.6
 
  85  8.19  10.3    11.7    13.9    14.9    16.0    18.4    19.7    20.8    22.6    22.6    22.6    22.6    22.6    26.0    33.7    38.7    44.4    47.6    47.6    44.4    41.5    33.7    27.4
  86  9.05  11.3    12.7    14.9    16.0    17.1    19.7    21.1    22.4    24.3    24.3    24.3    24.3    24.3    27.9    36.1    41.5    47.6    51.0    51.0    47.6    44.4    36.1    29.4
  87  10.0  12.1    13.9    16.0    17.1    18.4    21.1    22.6    24.0    26.0    26.0    26.0    26.0    26.0    29.9    38.7    44.4    51.0    54.7    54.7    51.0    47.6    38.7    31.5
  88  11.1  13.0    14.9    17.1    18.4    19.7    22.6    24.3    25.8    27.9    27.9    27.9    27.9    27.9    32.0    41.5    47.6    54.7    58.6    58.6    54.7    51.0    41.5    33.7
  89  12.2  13.9   16 .0    18.4    19.7    21.1    24.3    26.0    27.7    29.9    29.9    29.9    29.9    29.9    34.3    44.4    51.0    58.6    62.7    62.7    58.6    54.7    44.4    36.1
 
  90  13.5  14.9    17.1    19.7    21.1    22.6    26.0    27.9    29.7    32.0    32.0    32.0    32.0    32.0    36.8    47.6    54.7    62.7    67.2    67.2    62.7    58.6    47.6    38.7
  91  14.9  16.0    18.4    21.1    22.6    24.3    27.9    29.9    31.8    34.3    34.3    34.3    34.3    34.3    39.4    51.0    58.6    67.2    72.6    72.0    67.2    62.7    51.0    41.5
  92  16.0  17.1    19.7    22.6    24.3    26.0    29.9    32.0    34.2    36.8    36.8    36.8    36.8    36.8    42.2    54.7    62.7    72.0    77.2    77.2    72.0    67.2    54.7    44.4
  93  17.1  18.4    21.1    24.3    26.0    27.9    32.0    34.3    36.7    39.4    39.4    39.4    39.4    39.4    45.3    58.6    67.2    77.2    82.7    82.7    77.2    72.0    58.6    47.6
  94  18.4  19.7    22.6    26.0    27.9    29.9    34.3    36.8    39.4    42.2    42.2    42.2    42.2    42.2    48.5    62.7    72.0    82.7    88.6    88.6    82.7    77.2    62.7    51.0
 
  95  19.7  21.1    24.3    27.9    29.9    32.0    36.8    39.4    42.2    45.3    45.3    45.3    45.3    45.3    52.0    67.2    77.2    88.6    94.9    94.9    88.6    82.7    67.2    54.7
  96  21.1  22.6    26.0    29.9    32.0    34.3    39.4    42.2    45.3    48.5    48.5    48.5    48.5    48.5    55.7    72.0    82.7    94.9     102     102    94.9    88.6    72.0    58.6
  97  22.6  24.3    27.9    32.0    34.3    36.8    42.2    45.3    48.5    52.0    52.0    52.0    52.0    52.0    59.7    77.2    88.6     102     109     109     102    94.9    77.2    62.7
  98  24.3  26.0    29.9    34.3    36.8    39.4    45.3    48.5    52.0    55.7    55.7    55.7    55.7    55.7    64.0    82.7    94.9     109     117     117     105     102    82.7    67.2
  99  26.0  27.9    32.0    36.8    39.4    42.2    48.5    52.0    55.7    59.7    59.7    59.7    59.7    59.7    68.6    88.6     102     117     125     125     117     109    88.6    72.0
 
 100  27.9  29.9    34.3    39.4    42.2    45.3    52.0    55.7    59.7    64.0    64.0    64.0    64.0    64.0    73.5    94.9     109     125     134     134     125     117    94.9    77.2
 101  29.9  32.0    36.8    42.2    45.3    48.5    55.7    59.7    64.0    68.6    68.6    68.6    68.6    68.6    78.8     102     117     134     144     144     134     125     102    82.7
 102  32.0  34.3    39.4    45.3    48.5    52.0    59.7    64.0    68.6    73.5    73.5    73.5    73.5    73.5    84.4     109     125     144     154     154     144     134     109    88.6
 103  34.3  36.8    42.2    48.5    52.0    55.7    64.0    68.6    73.5    78.8    78.8    78.8    78.8    78.8    90.5     117     134     154     165     165     154     144     117    94.9
 104  36.8  39.4    45.3    52.0    55.7    59.7    68.6    73.5    78.8    84.4    84.4    84.4    84.4    84.4    97.0     125     144     165     177     177     165     154     125     102
 
 105  39.4  42.2    48.5    55.7    59.7    64.0    73.5    78.8    84.4    90.5    90.5    90.5    90.5    90.5     104     134     154     177     189     189     177     165     134     109
 106  42.2  45.3    52.0    59.7    64.0    68.6    78.8    84.4    90.5    97.0    97.0    97.0    97.0    97.0     111     144     165     189     203     203     189     177     144     117
 107  45.3  48.5    55.7    64.0    68.6    73.5    84.4    90.5    97.0     104     104     104     104     104     119     154     177     203     217     217     203     109     154     125
 108  48.5  52.0    59.7    68.6    73.5    78.8    90.5    97.0     104     111     111     111     111     111     128     165     189     217     233     233     217     203     165     134
 109  52.0  55.7    64.0    73.5    78.8    84.4    97.0     104     111     119     119     119     119     119     137     177     203     233     249     249     233     217     177     144
 
 110  55.7  59.7    68.6    78.8    84.4    90.5     104     111     119     128     128     128     128     128     137     189     217     249     267     267     249     233     189     154
 111  59.7  64.0    73.5    84.4    90.5    97.0     111     119     128     137     137     137     137     137     158     203     233     267     286     286     267     249     203     165
 112  64.0  68.6    78.8    90.4    97.0     104     119     128     137     147     147     147     147     147     169     217     249     286     307     307     286     267     217     177
 113  64.6  73.5    84.4    97.0     104     111     128     137     147     158     158     158     158     158     181     233     267     307     329     329     307     286     233     189
 114  73.5  78.8    50.5     104     111     119     137     147     158     169     169     169     169     169     194     249     286     329     352     352     329     307     249     203
 
 115  78.8  84.4    97.0     111     119     128     147     158     169     181     181     181     181     181     208     267     307     352     377     377     352     329     267     217
 116  84.4  90.5     104     119     128     137     158     169     181     194     194     194     194     194     223     286     329     377     404     404     377     352     286     233
 117  90.5  97.6     111     128     137     147     169     181     194     208     208     208     208     208     239     307     352     404     433     433     404     377     307     249
 118  97.0   104     119     137     147     158     181     194     208     223     223     223     223     223     256     329     377     433     464     464     433     404     329     267
 119   104   111     128     147     158     169     194     208     223     239     239     239     239     239     274     352     404     464     497     497     464     433     352     286
 
 120   111   119     137     158     169     181     208     223     239     256     256     256     256     256     294     377     433     497     533     533     497     464     377     307
 121   119   128     147     169     181     194     223     239     256     274     274     274     274     274     315     404     464     533     571     571     533     497     404     329
 122   128   137     158     181     194     208     239     256     274     294     294     294     294     294     338     433     497     571     611     611     571     533     433     352
 123   137   147     169     194     208     223     256     274     294     315     315     315     315     315     362     464     533     611     655     655     611     571     464     377
 124   147   158     181     208     223     239     274     294     315     338     338     338     338     338     388     497     571     655     702     702     655     611     497     404
 
 125   158   169     194     223     239     256     294     315     338     362     362     362     362     362     416     533     611     702     752     752     702     655     533     433
 126   169   181     208     239     256     274     315     338     362     388     388     388     388     388     446     571     655     752     806     806     752     702     571     464
 127   181   194     223     256     274     294     338     362     388     416     416     416     416     416     479     611     702     806     863     863     606     732     611     497
 128   194   208     239     274     294     315     362     388     416     446     446     446     446     446     512     655     752     863     925     925     863     806     655     533
 129   208   223     256     294     315     338     388     416     446     478     478     478     478     478     549     702     806     925     991     991     925     863     702     571
 
 130   223   239     274     315     338     362     416     446     478     512     512     512     512     512     588     752     863     991    1062    1062     991     925     752     611
 131   239   256     294     338     362     388     446     478     512     549     549     549     549     549     630     806     925    1062    1137    1137    1062     991     606     655
 132   256   274     315     362     388     416     478     512     549     588     588     588     588     588     676     863     991    1137    1219    1219    1137    1062     863     702
 133   274   294     338     388     416     446     512     549     588     630     630     630     630     630     724     925    1062    1219    1306    1306    1219    1137     925     752
 134   294   315     362     416     446     478     549     588     630     676     676     676     676     676     776     991    1137    1306    1399    1399    1306    1219     991     606
 
 135   315   338     388     446     478     512     588     630     676     724     724     724     724     724     832    1062    1219    1399    1499    1499    1399    1306    1062     863
 136   338   362     416     478     512     549     630     676     724     776     776     776     776     776     891    1137    1306    1499    1606    1606    1499    1399    1197     925
 137   362   388     446     512     549     588     676     724     776     832     832     832     832     832     955    1219    1399    1606    1721    1721    1606    1499    1219     991
 138   398   416     478     549     588     630     724     776     832     891     891     891     891     891    1024    1306    1499    1721    1844    1844    1721    1606    1306    1062
 139   416   446     512     588     630     676     776     832     891     955     955     955     955     955    1098    1399    1606    1844    1975    1975    1844    1721    1399    1137
 
 140   446   478     549     630     676     724     832     891     955    1024    1024    1024    1024    1024    1176    1499    1721    1975  ......  ......    1975    1844    1499    1219
 141   478   512     588     676     724     776     891     955    1024    1098    1098    1098    1098    1098    1261    1606    1844  ......  ......  ......  ......    1975    1606    1306
 142   512   549     630     724     776     832     955    1024    1098    1176    1176    1176    1176    1176    1351    1721    1975  ......  ......  ......  ......  ......    1721    1399
 143   549   588     676     776     832     891    1024    1098    1176    1261    1261    1261    1261    1261    1448    1844  ......  ......  ......  ......  ......  ......    1844    1499
 144   588   630     724     832     891     955    1098    1176    1261    1351    1351    1351    1351    1351    1552    1975  ......  ......  ......  ......  ......  ......    1975    1606
 
 145   630   676     776     891     955    1024    1176    1261    1351    1448    1448    1448    1448    1448    1664  ......  ......  ......  ......  ......  ......  ......  ......    1721
 146   676   724     832     955    1024    1098    1261    1351    1448    1552    1552    1552    1552    1552    1783  ......  ......  ......  ......  ......  ......  ......  ......    1844
 147   724   776     891    1024    1098    1176    1351    1448    1552    1664    1664    1664    1664    1664    1911  ......  ......  ......  ......  ......  ......  ......  ......    1975
 148   776   832     955    1098    1176    1261    1448    1552    1664    1783    1783    1783    1783    1783    2048  ......  ......  ......  ......  ......  ......  ......  ......  ......
 149   832   891    1024    1176    1261    1351    1552    1664    1783    1911    1911    1911    1911    1911  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......
 
 150   891   955    1098    1261    1351    1448    1664    1783    1911    2048    2048    2048    2048    2048  ......  ......  ......  ......  ......  ......  ......  ......  ......  ......
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Section B36.5 Correction for spectral irregularities. Noise having pronounced irregularities in the spectrum (for example, discrete frequency components or tones), must be adjusted by the correction factor C(k) calculated as follows:

(a) Step 1. Starting with the corrected sound pressure level in the 80 Hz one-third octave band (band number 3), calculate the changes in sound pressure level (or "slopes") in the remainder of the one-third octave bands as follows: s(3,k)=no value s(4,k)=SPL(4,k)−SPL(3,k) . . . s(i,k)=SPL(i,k)−SPL[(i−l),k] . . . s(24,k)=SPL(24,k)−SPL(23,k)

(b) Step 2. Encircle the value of the slope, s(i,k), where the absolute value of the change in slope is greater than 5; that is, where

∥ Δ s(i,k) ∥ = ∥ s(i,k)−s[(i−1),k] ∥ >5

(c) Step 3. (1) If the encircled value of the slope s(i,k) is positive and algebraically greater than the slope s[(i−1),k], encircle SPL(I,K).

(2) If the encircled value of the slope s(1,k) is zero or negative and the slope s[i−1),k] is positive, encircle (SPL[(i−1),k])

(3) For all other cases, no sound pressure level value is to be encircled.

(d) Step 4. Omit all SPL(i,k) encircled in Step 3 and compute new sound pressure levels SPL'prime;(i,k) as follows:

(1) For nonencircled sound pressure levels, let the new sound pressure levels equal the original sound pressure levels,

SPL'(i,k)=SPL(i,k)

(2) For encircled sound pressure levels in bands 1-23, let the new sound pressure level equal the arithmetic average of the preceding and following sound pressure levels.

SPL'(i,k)=( 1/2)[SPL[(i−1),k]+SPL[(i+1),k]]

(3) If the sound pressure level in the highest frequency band (i=24) is encircled, let the new sound pressure level in that band equal

SPL'(24,k)=SPL(23,k+s(23,k).

(e) Step 5. Recompute new slopes s' (i,k), including one for an imaginary 25-th band, as follows: s'(3,k)=s'(4,k) s'(4,k)=SPL'(4,k)−SPL'(3,k) . . . s'(i,k)=SPL'(i,k)−SPL'[(i−1),k] s'(24,k)=SPL'(24,k)−SPL'(23,k) s'(25,k)=s'(24,k)

(f) Step 6. For i from 3 to 23, compute the arithmetic average of the three adjacent slopes as follows:

s(i,k)=( 1/3)[s'(i,k)+s'[(i+1),k] +s'[(i+2),k]]

(g) Step 7. Compute final adjusted one-third octave-band sound pressure levels, SPL' (i,k), by beginning with band number 3 and proceeding to band number 24 as follows: SPL'(3,k)=SPL(3,k) SPL'(4,k)=SPL'(3.k)+s(3.k) . . . SPL'(i,k)=SPL'[(i−1),k]+s[(i−1),k] . . . SPL'(24,k)=SPL'(23,k)+s(23,k)

(h) Step 8. Calculate the differences, F(i,k), between the original and the adjusted sound pressure levels as follows:

F(i,k)=SPL(i,k)−SPL'(i,k)

and note only value greater than one and a half.

(i) Step 9. For each of the 24 one-third octave bands, determine tone correction factors from the sound pressure level differences F(i,k) and Table B2.

View or Download PDF

 
------------------------------------------------------------------------
                                   Level difference   Tone correction C,
         Frequency f, Hz                 F, dB                dB
------------------------------------------------------------------------
50<ls-thn-eq> f500..............  1\1/2\*<ls-thn-eq>  F/3-\1/2\
                                   F3.
                                  3<ls-thn-eq> F20..  F/6
                                  20<ls-thn-eq> F...  3\1/2\
 
                                 ---------------------------------------
500<ls-thn-eq> f<ls-thn-eq>5,000  1\1/2\*<ls-thn-eq>  2 F/3-1
                                   F3.
                                  3<ls-thn-eq> F20..  F/3
                                  20<ls-thn-eq> F...  6\2/3\
 
                                 ---------------------------------------
5,000 f<ls-thn-eq>10,000........  1\1/2\*<ls-thn-eq>  F/3-\1/2\
                                   F3.
                                  3<ls-thn-eq> F20..  F/6
                                  20<ls-thn-eq> F...  3\1/3\
------------------------------------------------------------------------
*See Step 8.

(j) Step 10. Designate the largest of the tone correction factors, determined in Step 9, as C(k). An example of the tone correction procedure is given in Table B3.

(k) Tone corrected perceived noise levels PNLT(k) are determined by adding the C(k) values to corresponding PNL(k) values, that is,

PNLT(k)=PNL(k)+C(k)

(l) For any i-th one-third octave band, at any k-th increment of time, for which the tone correction factor is suspected to result from something other than (or in addition to) an actual tone (or any special irregularity other than aircraft noise), an additional analysis may be made using a filter with a bandwidth narrower than one-third of an octave. If the narrow band analysis corroborates that suspicion, then a revised value for the background sound pressure level, SPL'(i,k) may be determined from the analysis and used to compute a revised tone correction factor, F(i,k), for that particular one-third octave band.

(m) Tones resulting from ground-plane reflections in the 800 Hz and lower one-third octave bands may be excluded from the calculation of corrections for spectral irregularities. To qualify for this exclusion, the pseudotones must be clearly identified as not being related to the engine noise. This identification may be made either by comparing measured data with data from a flush mounted microphone, or by observing the Doppler shift characteristics of the tone during the flyover-noise/time history. Since pseudotones are related to ground reflections, a microphone mounted flush to the ground will yield a spectral shape which can be distinguished from that produced by the 4-foot high microphone at those frequencies which can be related to ground reflection's geometrical relationships. Identification through Doppler shifting (the symmetric variation of frequency with time) can be made because the Doppler frequency variation yields a frequency increase for an approaching signal and a frequency decrease for a receding signal. Pseudotones at frequencies above 800 Hz generally should not yield significant tone corrections. However, for consistency, each tone correction value must be included in the computation for spectral irregularities. While the tone corrections below 800 Hz may be ignored for the spectral irregularity correction, the SPL values must be included in the noy calculation prescribed in section B36.13 of this appendix.

(n) After the value of PNLTM for each flyover-noise/time history, is identified, the frequency for the largest tone correction factor (C(k)) must be identified for the two preceding and the two succeeding, 500-milli-second time intervals, to identify possible tone suppression at PNLTM as a result of band sharing of the tone. If the value of C(k) for PNLTM is less than the average value of C(k) for those five consecutive time intervals, that average value of C(k) must be used to compute a new value for PNLTM.

Section B36.7 Maximum tone corrected perceived noise level. (a) The maximum tone corrected perceived noise level, PNLTM, is the maximum calculated value of the tone corrected perceived noise level, PNLT(k), calculated in accordance with the procedure of section B36.5 of this appendix. Figure B2 is an example of a flyover noise time history where the maximum value is clearly indicated. Half-second time intervals, Δ t, are small enough to obtain a satisfactory noise time history.

View or Download PDF

(b) If there are no pronounced irregularities in the spectrum, then the procedure of §B36.5 of this appendix would be redundant since PNLT(k) would be identically equal to PNL(k). For this case, PNLTM would be the maximum value of PNL(k) and would equal PNLM.

Section B36.9 Duration correction. The duration correction factor D is determined by the integration technique defined by the expression: $$

View or Download PDF

Where T is a normalizing time constant, PNLTM is the maximum value of PNLT, and t(1) and t(2) are the limits of the significant noise time history.

(a) Since PNLT is calculated from measured values of SPL, there will, in general, be no obvious equation for PNLT as a function of time. Consequently, the equation can be rewritten with a summation sign instead of an integral sign as follows: $$

where Δ t is the length of the equal increments of time for which PNLT(k) is calculated and d is the time interval to the nearest 1.0 second during which PNLT(k) is within a specified value, h, of PNLTM.

(b) Half-second time intervals for Δ t are small enough to obtain a satisfactory history of the perceived noise level. A shorter time interval may be selected by the applicant provided approved limits and constants are used.

(c) The following values for T, Δ t,and h, must be used in calculating D:

T=10 sec,

Δ t=0.5 sec.(or the approved sampling time interval), and

h=10 dB.

Using the above values, the equation for D becomes $$

Where the integer d is the duration time defined by the points that are 10 dB less than PNLTM.

(d) If the 10 dB-down points fall between calculated PNLT(k) values (the usual case), the applicable limits for the duration time must be chosen from the PNLT(k) values closest to PNLTM−10. For those cases with more than one peak value of PNLT(k), the applicable limits must be chosen to yield the largest possible value for the duration time.

(e) If the value of PNLT(k) at the 10 dB-down points is 90 PNdB or less, the value of d may be taken as the time interval between the initial and the final times for which PNLT(k) equals 90 PNdB.

(f) The aircraft testing procedures must include the 10 dB-down points in the flyover noise/time record.

Section B36.11 Effective perceived noise level. (a) The total subjective effect of an aircraft flyover is designated "effective perceived noise level," EPNL, and is equal to the algebraic sum of the maximum value of the tone corrected perceived noise level, PNLTM, and the duration correction, D. That is,

EPNL=PNLTM+D

where PNLTM and D are calculated under sections B36.7 and B36.9 of this appendix.

(b) The above equation can be rewritten by substituting the equation for D from §B36.9 of this appendix, that is, $$

(c) If, during a test flight, one or more peak values of PNLT are observed which are within 2 dB of PNLTM, the value of EPNL shall be calculated for each, as well as for PNLTM. If any EPNL value exceeds the value at the moment of PNLTM, the maximum value of such exceedance must be added as a further adjustment to the EPNL calculated from the measured data.

Section B36.13      Mathematical formulation of noy tables.

(a) The relationship between sound pressure level and perceived noisiness given in Table B1 is illustrated in Figure B3. The variation of log (n) with SPL for a given one-third octave band can be expressed by straight lines as shown in Figure B3.

(1) The slopes of the straight lines M(b), M(c), and M(d) and M(e);

(2) The intercepts of the lines on the SPL axis, SPL (b) and SPL (c); and

(3) The coordinates of the discontinuities, SPL (a) and log n(a); SPL (d) and log n = −1.0; and SPL (e) and log n = log (0.3).

(b) The important aspects of the mathematical formulation are:

(1) SPL ≥ SPL (a)
    n = antilog [M(c)*(SPL-SPL(c))]

(2) SPL (b) ≤ SPL < SPL (a)
    n = antilog [M(b)*(SPL-SPL(b))]

(3) SPL (e) ≤ SPL < SPL (b)
    n = antilog [M(e)*(SPL-SPL(b))]

(4) SPL (d) ≤ SPL < SPL (e)
    n = 0.1 antilog [M(d)*(SPL-SPL(d))]

(c) Table B4 lists the values of the important constants necessary to calculate sound pressure level as a function of perceived noisiness.

View or Download PDF

View or Download PDF

[Doc. No. 9337, 34 FR 18364, Nov. 18, 1969, as amended by Amdt. 36-5, 41 FR 35058, Aug. 19, 1976; Amdt. 36-9, 43 FR 8748, Mar. 2, 1978; Amdt. 36-14, 53 FR 3541, Feb. 5, 1988; Amdt. 36-15, 53 FR 16368, May 6, 1988]

C36.1      Noise measurement and evaluation.

C36.3      Noise measuring points.

C36.5      Noise levels.

C36.7      Takeoff reference and test limitations.

C36.9      Approach reference and test limitations.

Section C36.1 Noise measurement and evaluation. Compliance with this appendix must be shown with noise levels measured and evaluated as prescribed, respectively, by appendix A and appendix B of this part, or under approved equivalent procedures.

Section C36.3 Noise measuring points. Compliance with the noise level standards of section C36.5 must be shown --

(a) For takeoff, at a point 21, 325 feet (6,500 meters) from the start of the takeoff roll on the extended centerline of the runway;

(b) For approach, at a point 6,562 feet (2,000 meters) from the threshold on the extended centerline of the runway; and

(c) For the sideline, at the point, on a line parallel to and 1,476 feet (450 meters) from the extended centerline of the runway, where the noise level after liftoff is greatest, except that, for an airplane powered by more than three turbojet engines, this distance must be 0.35 nautical miles for the purpose of showing compliance with Stage 1 or Stage 2 noise limits (as applicable).

Sec. C36.5      Noise levels.

(a) Limits. Except as provided in paragraphs (b) and (c) of this section, it must be shown by flight test that the noise levels of the airplane, at the measuring points described in section C36.3, do not exceed the following (with appropriate interpolation between weights);

(1) Stage 1 noise limits for acoustical changes for airplanes regardless of the number of engines are those noise levels prescribed under §36.7(c) of this part.

(2) Stage 2 noise limits for airplanes regardless of the number of engines are as follows:

(i) For takeoff. 108 EPNdB for maximum weights of 600,000 pounds or more, reduced by 5 EPNdB per halving of the 600,000 pounds maximum weight down to 93 EPNdB for maximum weights of 75,000 pounds and less.

(ii) For sideline and approach. -- 108 EPNdB for maximum weights of 600,000 pounds or more, reduced by 2 EPNdB per halving of the 600,000 pounds maximum weight down to 102 EPNdB for maximum weights of 75,000 pounds and less.

(3) Stage 3 noise limits are as follows:

(i) For takeoff.

(A) For airplanes with more than 3 engines. 106 EPNdB for maximum weights of 850,000 pounds or more, reduced by 4 EPNdB per halving of the 850,000 pounds maximum weight down to 89 EPNdB for maximum weights of 44,673 pounds or less;

(B) For airplanes with 3 engines -- 104 EPNdB for maximum weights of 850,000 pounds or more, reduced by 4 EPNdB per halving of the 850,000 pounds maximum weight down to 89 EPNdB for maximum weights of 63,177 pounds and less; and

(C) For airplanes with fewer than 3 engines -- 101 EPNdB for maximum weights of 850,000 pounds or more, reduced by 4 EPNdB per halving of the 850,000 pounds maximum weight down to 89 EPNdB for maximum weights of 106,250 pounds and less.

(ii) For sideline, regardless of the number of engines. 103 EPNdB for maximum weights of 882,000 pounds or more, reduced by 2.56 EPNdB per halving of the 882,000 pounds maximum weight down to 94 EPNdB for maximum weights of 77,200 pounds or less.

(iii) For approach, regardless of the number of engines -- 105 EPNdB for maximum weights of 617,300 pounds or more, reduced by 2.33 EPNdB per halving of the 617,300 pounds weight down to 98 EPNdB for maximum weights of 77,200 pounds or less.

(b) Tradeoffs. Except to the extent limited under §§36.7(c)(1) and 36.7(d)(3)(i)(B) of this part, the noise level limits prescribed in paragraph (a) of this section may be exceeded at one or two of the measuring points specified in section C36.3 of this appendix, if --

(1) The sum of the exceedances is not greater than 3 EPNdB;

(2) No exceedance is greater than 2 EPNdB; and

(3) The exceedances are completely offset by reductions at other required measuring points.

Sec. C36.7      Takeoff Reference and Test Limitations.

(a) This section applies to all takeoff noise tests conducted under this appendix in showing compliance with this part.

(b) Takeoff power or thrust must be used from the start of takeoff roll to at least the following altitude above the runway:

(1) For Stage 1 airplanes and for Stage 2 airplanes that do not have turbojet engines with a bypass ratio of 2 or more, the following apply:

(i) For airplanes with more than three turbojet engines -- 700 feet (214 meters).

(ii) For all other airplanes -- 1,000 feet (305 meters).

(2) For Stage 2 airplanes that have turbojet engines with a bypass ratio of 2 or more and for Stage 3 airplane, the following apply:

(i) For airplanes with more than three turbojet engines -- 689 feet (210 meters).

(ii) For airplanes with three turbojet engines -- 853 feet (260 meters).

(iii) For airplanes with fewer than three turbojet engines -- 984 feet (300 meters).

(iv) For airplanes not powered by turbojet engines -- 1,000 feet (305 meters).

(c) Upon reaching the altitude specified in paragraph (b) of this section, the power or thrust may not be reduced below that needed to maintain level flight with one engine inoperative, or to maintain a four percent climb gradient, whichever power or thrust is greater.

(d) A constant takeoff configuration, selected by the applicant, must be maintained throughout the takeoff noise test, except that the landing gear may be retracted.

(e) For applications made for subsonic airplanes after September 17, 1971, and for Concorde airplanes, the following apply:

(1) For subsonic airplanes the test day speeds and the acoustic day reference speed must be the minimum approved value of V2+10 knots, or the all-engines-operating speed at 35 feet (for turbine engine powered airplanes) or 50 feet (for reciprocating engine powered airplanes), whichever speed is greater as determined under the regulations constituting the type certification basis of the airplane. These tests must be conducted at the test day speeds±3 knots. Noise values measured at the test day speeds must be corrected to the acoustic day reference speed.

(2) For Concorde airplanes, the test day speeds and the acoustic day reference speed must be the minimum approved value of V2 +35 knots, or the all-engines-operating speed at 35 feet, whichever speed is greater as determined under the regulations constituting the type certification basis of the airplane, except that the reference speed may not exceed 250 knot. These tests must be conducted at the test day speeds ±3 knots. Noise values measured at the test day speeds must be corrected to the acoustic day reference speed.

(3) If a negative runway gradient exists in the direction of takeoff, performance and acoustic data must be corrected to the zero slope condition.

Sec. C36.9      Approach reference and test limitations.

(a) This section applies to all approaches conducted in showing compliance with this part.

(b) The airplane's configuration must be that used in showing compliance with the landing requirements in the airworthiness regulations constituting the type certification basis of the airplane. If more than one configuration is used in showing compliance with the landing requirements in the airworthiness regulations constituting the type certification basis of the airplane, the configuration that is most critical from a noise standpoint must be used.

(c) The approaches must be conducted with a steady glide angle of 3°±0.5° and must be continued to a normal touchdown with no airframe configuration change.

(d) All engines must be operating at approximately the same power or thrust.

(e) For applications made for subsonic airplanes after September 17, 1971, and for Concorde airplanes, the following apply:

(1) For subsonic airplanes a steady approach speed, that is either 1.30 Vs +10 knots or the speed used in establishing the approved landing distance under the airworthiness regulations constituting the type certification basis of the airplane, whichever speed is greatest, must be established and maintained over the approach measuring point.

(2) For Concorde airplanes a steady approach speed, that is either the landing reference speed + 10 knots or the speed used in establishing the approved landing distance under the airworthiness regulations constituting the type certification basis of the airplane, whichever speed is greater, must be established and maintained over the approach measuring point.

(3) A tolerance of ±3 knots may be used throughout the approach noise testing.

F36.1      Scope.

F36.101      General test conditions.

F36.103      Acoustical measurement system.

F36.105      Sensing, recording, and reproducing equipment.

F36.107      Noise measurement procedures.

F36.109      Data recording, reporting, and approval.

F36.111      Flight procedures.

F36.201      Correction of data.

F36.203      Validity of results.

F36.301      Aircraft noise limits.

Section F36.1    Scope. This appendix prescribes noise level limits and procedures for measuring and correcting noise data for the propeller driven small airplanes specified in §§36.1 and 36.501(b).

Sec. F36.101       General test conditions.

(a) The test area must be relatively flat terrain having no excessive sound absorption characteristics such as those caused by thick, matted, or tall grass, by shrubs, or by wooded areas. No obstructions which significantly influence the sound field from the airplane may exist within a conical space above the measurement position, the cone being defined by an axis normal to the ground and by a half-angle 75 degrees from this axis.

(b) The tests must be carried out under the following conditions:

(1) There may be no precipitation.

(2) Relative humidity may not be higher than 90 percent or lower than 30 percent.

(3) Ambient temperature may not be above 86 degrees F. or below 41 degrees F. at 33&foot; above ground. If the measurement site is within 1 n.m. of an airport thermometer the airport reported temperature may be used.

(4) Reported wind may not be above 10 knots at 33&foot; above ground. If wind velocities of more than 4 knots are reported, the flight direction must be aligned to within ±15 degrees of wind direction and flights with tail wind and head wind must be made in equal numbers. If the measurement site is within 1 n.m. of an airport anemometer, the airport reported wind may be used.

(5) There may be no temperature inversion or anomalous wind conditions that would significantly alter the noise level of the airplane when the noise is recorded at the required measuring point.

(6) The flight test procedures, measuring equipment, and noise measurement procedures must be approved by the FAA.

(7) Sound pressure level data for noise evaluation purposes must be obtained with acoustical equipment that complies with section F36.103 of this appendix.

Sec. F36.103       Acoustical measurement system. The acoustical measurement system must consist of approved equipment equivalent to the following:

(a) A microphone system with frequency response compatible with measurement and analysis system accuracy as prescribed in section F36.105 of this appendix.

(b) Tripods or similar microphone mountings that minimize interference with the sound being measured.

(c) Recording and reproducing equipment characteristics, frequency response, and dynamic range compatible with the response and accuracy requirements of section F36.105 of this appendix.

(d) Acoustic calibrators using sine wave or broadband noise of known sound pressure level. If broadband noise is used, the signal must be described in terms of its average and maximum root-mean-square (rms) value for nonoverload signal level.

Sec. F36.105       Sensing, recording, and reproducing equipment.

(a) The noise produced by the airplane must be recorded. A magnetic tape recorder is acceptable.

(b) The characteristics of the system must comply with the recommendations in International Electrotechnical Commission (IEC) Publication No. 179, entitled "Precision Sound Level Meters" as incorporated by reference in Part 36 under §36.6 of this part.

(c) The response of the complete system to a sensibly plane progressive sinusoidal wave of constant amplitude must lie within the tolerance limits specified in IEC Publication No. 179, dated 1973, over the frequency range 45 to 11,200 Hz.

(d) If limitations of the dynamic range of the equipment make it necessary, high frequency pre-emphasis must be added to the recording channel with the converse de-emphasis on playback. The pre-emphasis must be applied such that the instantaneous recorded sound pressure level of the noise signal between 800 and 11,200 Hz does not vary more than 20 dB between the maximum and minimum one-third octave bands.

(e) If requested by the Administrator, the recorded noise signal must be read through an "A" filter with dynamic characteristics designated "slow," as defined in IEC Publication No. 179, dated 1973. The output signal from the filter must be fed to a rectifying circuit with square law rectification, integrated with time constants for charge and discharge of about 1 second or 800 milliseconds.

(f) The equipment must be acoustically calibrated using facilities for acoustic freefield calibration and if analysis of the tape recording is requested by the Administrator, the analysis equipment shall be electronically calibrated by a method approved by the FAA.

(g) A windscreen must be employed with microphone during all measurements of aircraft noise when the wind speed is in excess of 6 knots.

Sec. F36.107       Noise measurement procedures.

(a) The microphones must be oriented in a known direction so that the maximum sound received arrives as nearly as possible in the direction for which the microphones are calibrated. The microphone sensing elements must be approximately 4&foot; above ground.

(b) Immediately prior to and after each test; a recorded acoustic calibration of the system must be made in the field with an acoustic calibrator for the two purposes of checking system sensitivity and providing an acoustic reference level for the analysis of the sound level data.

(c) The ambient noise, including both acoustical background and electrical noise of the measurement systems, must be recorded and determined in the test area with the system gain set at levels that will be used for aircraft noise measurements. If aircraft sound pressure levels do not exceed the background sound pressure levels by at least 10 dB(A), approved corrections for the contribution of background sound pressure level to the observed sound pressure level must be applied.

Sec. F36.109       Data recording, reporting, and approval.

(a) Data representing physical measurements or corrections to measured data must be recorded in permanent form and appended to the record except that corrections to measurements for normal equipment response deviations need not be reported. All other corrections must be approved. Estimates must be made of the individual errors inherent in each of the operations employed in obtaining the final data.

(b) Measured and corrected sound pressure levels obtained with equipment conforming to the specifications described in section F36.105 of this appendix must be reported.

(c) The type of equipment used for measurement and analysis of all acoustic, airplane performance, and meteorological data must be reported.

(d) The following atmospheric data, measured immediately before, after, or during each test at the observation points prescribed in section F36.101 of this appendix must be reported:

(1) Air temperature and relative humidity.

(2) Maximum, minimum, and average wind velocities.

(e) Comments on local topography, ground cover, and events that might interfere with sound recordings must be reported.

(f) The following airplane information must be reported:

(1) Type, model and serial numbers (if any) of airplanes, engines, and propellers.

(2) Any modifications or nonstandard equipment likely to affect the noise characteristics of the airplane.

(3) Maximum certificated takeoff weights.

(4) Airspeed in knots for each overflight of the measuring point.

(5) Engine performance in terms of revolutions per minute and other relevant parameters for each overflight.

(6) Aircraft height in feet determined by a calibrated altimeter in the aircraft, approved photographic techniques, or approved tracking facilities.

(g) Aircraft speed and position and engine performance parameters must be recorded at an approved sampling rate sufficient to ensure compliance with the test procedures and conditions of this appendix.

Sec. F36.111       Flight procedures.

(a) Tests to demonstrate compliance with the noise level requirements of this appendix must include at least six level flights over the measuring station at a height of 1,000&foot; ±30&foot; and ±10 degrees from the zenith when passing overhead.

(b) Each test over flight must be conducted:

(1) At not less than the highest power in the normal operating range provided in an Airplane Flight Manual, or in any combination of approved manual material, approved placard, or approved instrument markings; and

(2) At stabilized speed with propellers synchronized and with the airplane in cruise configuration, except that if the speed at the power setting prescribed in this paragraph would exceed the maximum speed authorized in level flight, accelerated flight is acceptable.

Sec. F36.201       Correction of data.

(a) Noise data obtained when the temperature is outside the range of 68 degrees F. ±9 degrees F., or the relative humidity is below 40 percent, must be corrected to 77 degrees F. and 70 percent relative humidity by a method approved by the FAA.

(b) The performance correction prescribed in paragraph (c) of this section must be used. It must be determined by the method described in this appendix, and must be added algebraically to the measured value. It is limited to 5dB(A).

(c) The performance correction must be computed by using the following formula: $$

Where: D50=Takeoff distance to 50 feet at maximum certificated takeoff weight. R/C=Certificated best rate of climb (fpm). Vy=Speed for best rate of climb in the same units as rate of climb.

(d) When takeoff distance to 50&foot; is not listed as approved performance information, the figures of 2000 for single-engine airplanes and 1600&foot; for multi-engine airplanes must be used.

Sec. F36.203       Validity of results.

(a) The test results must produce an average dB(A) and its 90 percent confidence limits, the noise level being the arithmetic average of the corrected acoustical measurements for all valid test runs over the measuring point.

(b) The samples must be large enough to establish statistically a 90 pecent confidence limit not to exceed ±1.5 dB(A). No test result may be omitted from the averaging process, unless omission is approved by the FAA.

Sec. F36.301       Aircraft noise limits.

(a) Compliance with this section must be shown with noise data measured and corrected as prescribed in Parts B and C of this appendix.

(b) For airplanes for which application for a type certificate is made on or after October 10, 1973, the noise level must not exceed 68 dB(A) up to and including aircraft weights of 1,320 pounds (600 kg.). For weights greater than 1,320 pounds up to and including 3,630 pounds (1.650 kg.) the limit increases at the rate of 1 dB/165 pounds (1 dB/75 kg.) to 82 dB(A) at 3,630 pounds, after which it is constant at 82 dB(A). However, airplanes produced under type certificates covered by this paragraph must also meet paragraph (d) of this section for the original issuance of standard airworthiness certificates or restricted category airworthiness certificates if those airplanes have not had flight time before the date specified in that paragraph.

(c) For airplanes for which application for a type certificate is made on or after January 1, 1975, the noise levels may not exceed the noise limit curve prescribed in paragraph (b) of this section, except that 80 dB(A) may not be exceeded.

(d) For airplanes for which application is made for a standard airworthiness certificate or for a restricted category airworthiness certificate, and that have not had any flight time before January 1, 1980, the requirements of paragraph (c) of this section apply, regardless of date of application, to the original issuance of the certificate for that airplane.

G36.1      Scope.

G36.101      General Test Conditions.

G36.103      Acoustical measurement system.

G36.105      Sensing, recording, and reproducing equipment.

G36.107      Noise measurement procedures.

G36.109      Data recording, reporting, and approval.

G36.111      Flight procedures.

G36.201      Corrections to Test Results.

G36.203      Validity of results.

G36.301      Aircraft Noise Limits.

Section G36.1    Scope. This appendix prescribes limiting noise levels and procedures for measuring noise and adjusting these data to standard conditions, for propeller driven small airplanes and propeller-driven, commuter category airplanes specified in §§36.1 and 36.501(c).

Sec. G36.101    General Test Conditions.

(a) The test area must be relatively flat terrain having no excessive sound absorption characteristics such as those caused by thick, matted, or tall grass, by shrubs, or by wooded areas. No obstructions which significantly influence the sound field from the airplane may exist within a conical space above the measurement position, the cone being defined by an axis normal to the ground and by a half-angle 75 degrees from the normal ground axis.

(b) The tests must be carried out under the following conditions:

(1) No precipitation;

(2) Ambient air temperature between 36 and 95 degrees F (2.2 and 35 degrees C);

(3) Relative humidity between 20 percent and 95 percent, inclusively;

(4) Wind speed may not exceed 10 knots (19 km/h) and cross wind may not exceed 5 knots (9 km/h), using a 30-second average;

(5) No temperature inversion or anomalous wind condition that would significantly alter the noise level of the airplane when the nose is recorded at the required measuring point, and

(6) The meteorological measurements must be made between 4 ft. (1.2 m) and 33 ft. (10 m) above ground level. If the measurement site is within 1 n.m. of an airport meteorological station, measurements from that station may be used.

(c) The flight test procedures, measuring equipment, and noise measurement procedures must be approved by the FAA.

(d) Sound pressure level data for noise evaluation purposes must be obtained with acoustical equipment that complies with section G36.103 of this appendix.

Sec. G36.103    Acoustical Measurement System.

The acoustical measurement system must consist of approved equipment with the following characteristics: (a) A microphone system with frequency response compatible with measurement and analysis system accuracy as prescribed in section G36.105 of this appendix.

(b) Tripods or similar microphone mountings that minimize interference with the sound being measured.

(c) Recording and reproducing equipment characteristics, frequency response, and dynamic range compatible with the response and accuracy requirements of section G36.105 of this appendix.

(d) Acoustic calibrators using sine wave or broadband noise of known sound pressure level. If broadband noise is used, the signal must be described in terms of its average and maximum root-mean-square (rms) value for non-overload signal level.

Sec. G36.105    Sensing, Recording, and Reproducing Equipment.

(a) The noise produced by the airplane must be recorded. A magnetic tape recorder, graphic level recorder, or sound level meter is acceptable when approved by the regional certificating authority.

(b) The characteristics of the complete system must comply with the requirements in International Electrotechnical Commission (IEC) Publications No. 651, entitled "Sound Level Meters" and No. 561, entitled "Electro-acoustical Measuring Equipment for Aircraft Noise Certification" as incorporated by reference under §36.6 of this part. Sound level meters must comply with the requirements for Type 1 sound level meters as specified in IEC Publication No. 651.

(c) The response of the complete system to a sensibly plane progressive sinusoidal wave of constant amplitude must be within the tolerance limits specified in IEC Publication No. 651, over the frequency range 45 to 11,200 Hz.

(d) If equipment dynamic range limitations make it necessary, high frequency pre-emphasis must be added to the recording channel with the converse de-emphasis on playback. The pre-emphasis must be applied such that the instantaneous recorded sound pressure level of the noise signal between 800 and 11,200 Hz does not vary more than 20 dB between the maximum and minimum one-third octave bands.

(e) The output noise signal must be read through an "A" filter with dynamic characteristics designated "slow" as defined in IEC Publication No. 651. A graphic level recorder, sound level meter, or digital equivalent may be used.

(f) The equipment must be acoustically calibrated using facilities for acoustic free-field calibration and if analysis of the tape recording is requested by the Administrator, the analysis equipment shall be electronically calibrated by a method approved by the FAA. Calibrations shall be performed, as appropriate, in accordance with paragraph A36.3(e) of appendix A of this part.

(g) A windscreen must be employed with the microphone during all measurements of aircraft noise when the wind speed is in excess of 5 knots (9 km/hr).

Sec. G36.107      Noise Measurement Procedures.

(a) The microphone must be a pressure type, 12.7 mm in diameter, with a protective grid, mounted in an inverted position such that the microphone diaphragm is 7 mm above and parallel to a white-painted metal circular plate. This white-painted metal plate shall be 40 cm in diameter and at least 2.5 mm thick. The plate shall be placed horizontally and flush with the surrounding ground surface with no cavities below the plate. The microphone must be located three-quarters of the distance from the center to the back edge of the plate along a radius normal to the line of flight of the test airplane.

(b) Immediately prior to and after each test, a recorded acoustic calibration of the system must be made in the field with an acoustic calibrator for the purposes of checking system sensitivity and providing an acoustic reference level for the analysis of the sound level data. If a tape recorder or graphic level recorder is used, the frequency response of the electrical system must be determined at a level within 10 dB of the full-scale reading used during the test, utilizing pink or pseudorandom noise.

(c) The ambient noise, including both acoustic background and electrical systems noise, must be recorded and determined in the test area with the system gain set at levels which will be used for aircraft noise measurements. If aircraft sound pressure levels do not exceed the background sound pressure levels by at least 10 dB(A), a takeoff measurement point nearer to the start of the takeoff roll must be used and the results must be adjusted to the reference measurement point by an approved method.

Sec. G36.109      Data Recording, Reporting, and Approval.

(a) Data representing physical measurements and adjustments to measured data must be recorded in permanent form and appended to the record, except that corrections to measurements for normal equipment response deviations need not be reported. All other adjustments must be approved. Estimates must be made of the individual errors inherent in each of the operations employed in obtaining the final data.

(b) Measured and corrected sound pressure levels obtained with equipment conforming to the specifications in section G36.105 of this appendix must be reported.

(c) The type of equipment used for measurement and analysis of all acoustical, airplane performance, and meteorological data must be reported.

(d) The following atmospheric data, measured immediately before, after, or during each test at the observation points prescribed in section G36.101 of this appendix must be reported:

(1) Ambient temperature and relative humidity.

(2) Maximum and average wind speeds and directions for each run.

(e) Comments on local topography, ground cover, and events that might interfere with sound recordings must be reported.

(f) The aircraft position relative to the takeoff reference flight path must be determined by an approved method independent of normal flight instrumentation, such as radar tracking, theodolite triangulation, or photographic scaling techniques.

(g) The following airplane information must be reported:

(1) Type, model, and serial numbers (if any) of airplanes, engines, and propellers;

(2) Any modifications or nonstandard equipment likely to affect the noise characteristics of the airplane;

(3) Maximum certificated takeoff weight;

(4) For each test flight, airspeed and ambient temperature at the flyover altitude over the measuring site determined by properly calibrated instruments;

(5) For each test flight, engine performance parameters, such as manifold pressure or power, propeller speed (rpm) and other relevant parameters. Each parameter must be determined by properly calibrated instruments. For instance, propeller RPM must be validated by an independent device accurate to within ±1 percent, when the airplane is equipped with a mechanical tachometer.

(6) Airspeed, position, and performance data necessary to make the corrections required in section G36.201 of this appendix must be recorded by an approved method when the airplane is directly over the measuring site.

Sec. G36.111      Flight Procedures.

(a) The noise measurement point is on the extended centerline of the runway at a distance of 8200 ft (2500 m) from the start of takeoff roll. The aircraft must pass over the measurement point within ±10 degrees from the vertical and within 20% of the reference altitude. The flight test program shall be initiated at the maximum approved takeoff weight and the weight shall be adjusted back to this maximum weight after each hour of flight time. Each flight test must be conducted at the speed for the best rate of climb (Vy) ±5 knots (±9 km/hour) indicated airspeed. All test, measurement, and data correction procedures must be approved by the FAA.

(b) The takeoff reference flight path must be calculated for the following atmospheric conditions:

(1) Sea level atmospheric pressure of 1013.25 mb (013.25 hPa);

(2) Ambient air temperature of 59 °F (15 °C);

(3) Relative humidity of 70 percent; and

(4) Zero wind.

(c) The takeoff reference flight path must be calculated assuming the following two segments:

(1) First segment.

(i) Takeoff power must be used from the brake release point to the point at which the height of 50 ft (15m) above the runway is reached.

(ii) A constant takeoff configuration selected by the applicant must be maintained through this segment.

(iii) The maximum weight of the airplane at brake-release must be the maximum for which noise certification is requested.

(iv) The length of this first segment must correspond to the airworthiness approved value for a takeoff on a level paved runway (or the corresponding value for seaplanes).

(2) Second segment.

(i) The beginning of the second segment corresponds to the end of the first segment.

(ii) The airplane must be in the climb configuration with landing gear up, if retractable, and flap setting corresponding to normal climb position throughout this second segment.

(iii) The airplane speed must be the speed for the best rate of climb (Vy).

(iv) Maximum continuous installed power and rpm for variable pitch propeller(s) shall be used. For fixed pitch propeller(s), the maximum power and rpm that can be delivered by the engine(s) must be maintained throughout the second segment.

Sec. G36.201 Corrections to Test Results.

(a) These corrections account for the effects of:

(1) Differences in atmospheric absorption of sound between meteorological test conditions and reference conditions.

(2) Differences in the noise path length between the actual airplane flight path and the reference flight path.

(3) The change in the helical tip Mach number between test and reference conditions.

(4) The change in the engine power between test and reference conditions.

(b) Atmospheric absorption correction is required for noise data obtained when the test conditions are outside those specified in Figure G1. Noise data outside the applicable range must be corrected to 59 F and 70 percent relative humidity by an FAA approved method.

View or Download PDF

(c) Helical tip Mach number and power corrections must be made as follows:

(1) Corrections for helical tip Mach number and power corrections must be made if --

(i) The propeller is a variable pitch type; or

(ii) The propeller is a fixed pitch type and the test power is not within 5 percent of the reference power.

(2) No corrections for helical tip Mach number variation need to be made if the propeller helical tip Mach number is:

(i) At or below 0.70 and the test helical tip Mach number is within 0.014 of the reference helical tip Mach number.

(ii) Above 0.70 and at or below 0.80 and the test helical tip Mach number is within 0.007 of the reference helical tip Mach number.

(iii) Above 0.80 and the test helical tip Mach number is within 0.005 of the reference helical tip Mach number. For mechanical tachometers, if the helical tip Mach number is above 0.8 and the test helical tip Mach number is within 0.008 of the reference helical tip Mach number.

(d) When the test conditions are outside those specified, corrections must be applied by an approved procedure or by the following simplified procedure:

(1) Measured sound levels must be corrected from test day meteorological conditions to reference conditions by adding an increment equal to

Delta (M) = (HT α -- 0.7 HR) /1000

where HT is the height in feet under test conditions, HR is the height in feet under reference conditions when the aircraft is directly over the noise measurement point and a is the rate of absorption for the test day conditions at 500 Hz as specified in SAE ARP 866A, entitled "Standard Values of Atmospheric Absorption as a function of Temperature and Humidity for use in Evaluating Aircraft Flyover Noise" as incorporated by reference under §36.6.

(2) Measured sound levels in decibels must be corrected for height by algebraically adding an increment equal to Delta (1). When test day conditions are within those specified in figure G1:

Delta (1) = 22 log (HT/HR)

where HT is the height of the test aircraft when directly over the noise measurement point and HR is the reference height.

When test day conditions are outside those specified in figure G1:

Delta (1) = 20 log (HT/HR)

(3) Measured sound levels in decibels must be corrected for helical tip Mach number by algebraically adding an increment equal to:

Delta (2) = k log (MR/MT)

where MT and MR are the test and reference helical tip Mach numbers, respectively. The constant "k" is equal to the slope of the line obtained for measured values of the sound level in dB(A) versus helical tip Mach number. The value of k may be determined from approved data. A nominal value of k = 150 may be used when MT is smaller than MR. No correction may be made using the nominal value of k when MT is larger than MR. The reference helical tip Mach number MR is the Mach number corresponding to the reference conditions (RPM, airspeed, temperature) above the measurement point.

(4) Measured sound levels in decibels must be corrected for engine power by algebraically adding an increment equal to

Delta(3) = K3 log (PR/PT)

where PR and PT are the test and reference engine powers respectively obtained from the manifold pressure/torque gauges and engine rpm. The value of K3 shall be determined from approved data from the test airplane. In the absence of flight test data and at the discretion of the Administrator, a value of K3 = 17 may be used.

Sec. G36.203 Validity of Results.

(a) The measuring point must be overflown at least six times. The test results must produce an average noise level (LAmax) value within a 90 percent confidence limit. The average noise level is the arithmetic average of the corrected acoustical measurements for all valid test runs over the measuring point.

(b) The samples must be large enough to establish statistically a 90 percent confidence limit not exceeding ±1.5 dB(A). No test results may be omitted from the averaging process unless omission is approved by the FAA.

Sec. G36.301 Aircraft noise limits.

(a) Compliance with this section must be shown with noise data measured and corrected as prescribed in Parts B and C of this appendix.

(b) The noise level must not exceed 76 dB (A) up to and including aircraft weights of 1,320 pounds (600 kg). For aircraft weights greater than 1,320 pounds, the limit increases from that point with the logarithm of airplane weight at the rate of 9.83 dB (A) per doubling of weight, until the limit of 88 dB (A) is reached, after which the limit is constant up to and including 19,000 pounds (8,618 kg). Figure G2 shows noise level limits vs airplane weight.

View or Download PDF

PART A -- REFERENCE CONDITIONS Sec.

H36.1      General.

H36.3      Reference Test Conditions.

H36.5      Symbols and Units.

PART B -- NOISE MEASUREMENT UNDER §36.801

H36.101      Noise certification test and measurement conditions.

H36.103      Takeoff test conditions.

H36.105      Flyover test conditions.

H36.107      Approach test conditions.

H36.109      Measurement of helicopter noise received on the ground.

H36.111      Reporting and correcting measured data.

H36.113      Atmospheric attenuation of sound.

PART C -- NOISE EVALUATION AND CALCULATION UNDER §36.803

H36.201      Noise evaluation in EPNdB.

H36.203      Calculation of noise levels.

H36.205      Detailed data correction procedures.

PART D -- NOISE LIMITS UNDER §36.805

H36.301      Noise measurement, evaluation, and calculation.

H36.303      [Reserved]

H36.305      Noise levels.

Section H36.1 General. This appendix prescribes noise requirements for helicopters specified under §36.1, including:

(a) The conditions under which helicopter noise certification tests under Part H must be conducted and the measurement procedures that must be used under §36.801 to measure helicopter noise during each test;

(b) The procedures which must be used under §36.803 to correct the measured data to the reference conditions and to calculate the noise evaluation quantity designated as Effective Perceived Noise Level (EPNL); and

(c) The noise limits for which compliance must be shown under §36.805.

Section H36.3 Reference Test Conditions.

(a) Meteorological conditions. Aircraft position, performance data and noise measurements must be corrected to the following noise certification reference atmospheric conditions which shall be assumed to exist from the surface to the aircraft altitude:

(1) Sea level pressure of 2116 psf (76 cm mercury).

(2) Ambient temperature of 77 degrees F (25 degrees C).

(3) Relative humidity of 70 percent.

(4) Zero wind.

(b) Reference test site. The reference test site is flat and without line-of-sight obstructions across the flight path that encompasses the 10 dB down points.

(c) Takeoff reference profile. (1) Figure H1 illustrates a typical takeoff profile, including reference conditions.

(2) The reference flight path is defined as a straight line segment inclined from the starting point (1640 feet prior to the center microphone location at 65 feet above ground level) at an angleβ defined by the certificated best rate of climb and Vy for minimum engine performance. The constant climb angleβ is derived from the manufacturer's data (FAA-approved by the FAA) to define the flight profile for the reference conditions. The constant climb angleβ is drawn through Cr and continues, crossing over station A, to the position corresponding to the end of the type certification takeoff path represented by position Ir.

(d) Level flyover reference profile. The beginning of the level flyover reference profile is represented by helicopter position D (Figure H2). The helicopter approaches position D in level flight 492 feet above ground level as measured at station A. Airspeed is stabilized at either 0.9 VH or 0.45 VH + 65 knots (0.45 VH + 120 km/hr), whichever speed is less. Rotor speed is stabilized at the maximum continuous RPM throughout the 10 dB down time period. The helicopter crosses station A in level flight and proceeds to position J.

(e) For noise certification purposes, VH is defined as the airspeed in level flight obtained using the minimum specification engine torque corresponding to maximum continuous power available for sea level, 25 °C ambient conditions at the relevant maximum certificated weight. The value of VH thus defined must be listed in the Rotorcraft Flight Manual.

(f) Approach reference profile. (1) Figure H3 illustrates approach profile, including reference conditions.

(i) The beginning of the approach profile is represented by helicopter position E. The position of the helicopter is recorded for a sufficient distance (EK) to ensure recording of the entire interval during which the measured helicopter noise level is within 10 dB of Maximum Tone Corrected Perceived Noise Level (PNLTM), as required. EK represents a stable flight condition in terms of torque, rpm, indicated airspeed, and rate of descent resulting in a 6° ±0.5° approach angle.

(ii) The approach profile is defined by the approach angle β passing directly over the station A at a height of AH, to position K, which terminates the approach noise certification profile.

(2) The helicopter approaches position H along a constant 6° approach slope throughout the 10 dB down time period. The helicopter crosses position E and proceeds along the approach slope crossing over station A until it reaches position K.

Section H36.5 Symbols and units. The following symbols and units as used in this appendix for helicopter noise certification have the following meanings.

                Flight Profile Identification--Positions
------------------------------------------------------------------------
             Position                           Description
------------------------------------------------------------------------
A................................  Location of the noise measuring point
                                    at the flight-track noise measuring
                                    station vertically below the
                                    reference (takeoff, flyover, or
                                    approach) flight path.
C................................  Start of noise certification takeoff
                                    flight path.
C<INF>r</INF>...............................  Start of noise certification
                                    reference takeoff flight path.
D................................  Start of noise certification flyover
                                    flight path.
D<INF>r</INF>...............................  Start of noise certification
                                    reference flyover path.
E................................  Start of noise certification approach
                                    flight path.
E<INF>r</INF>...............................  Start of noise certification
                                    reference approach flight path.
F................................  Position on takeoff flight path
                                    directly above noise measuring
                                    station A.
G................................  Position on flyover flight path
                                    directly above noise measuring
                                    station A.
H................................  Position on approach flight path
                                    directly above noise measuring
                                    station A.
I................................  End of noise type certification
                                    takeoff flight path.
I<INF>r</INF>...............................  End of noise type certification
                                    reference takeoff flight path.
J................................  End of noise type certification
                                    flyover flight path.
J<INF>r</INF>...............................  End of noise type certification
                                    reference flyover flight path.
K................................  End of noise certification approach
                                    type flight path.
K<INF>r</INF>...............................  End of noise type certification
                                    reference approach flight path.
L................................  Position on measured takeoff flight
                                    path corresponding to PNLTM at
                                    station A.
L<INF>r</INF>...............................  Position on reference takeoff flight
                                    path corresponding to PNLTM of
                                    station A.
M................................  Position on measured flyover flight
                                    path corresponding to PNLTM of
                                    station A.
M<INF>r</INF>...............................  Position on reference flyover flight
                                    path corresponding to PNLTM of
                                    station A.
N................................  Position on measured approach flight
                                    path corresponding to PNLTM at
                                    station A.
N<INF>r</INF>...............................  Position on reference approach flight
                                    path corresponding to PNLTM at
                                    station A.
S................................  Position on measured approach path
                                    nearest to station A.
S<INF>r</INF>...............................  Position on reference approach path
                                    nearest to station A.
T................................  Position on measured takeoff path
                                    nearest to station A.
T<INF>r</INF>...............................  Position on reference takeoff path
                                    nearest to station A.
------------------------------------------------------------------------

                        Flight Profile Distances
------------------------------------------------------------------------
        Distance                Unit                   Meaning
------------------------------------------------------------------------
AF.....................  Feet..............  Takeoff Height. The
                                              vertical distance between
                                              helicopter and station A.
AG.....................  Feet..............  Flyover Height. The
                                              vertical distance between
                                              the helicopter and station
                                              A.
AH.....................  Feet..............  Approach Height. The
                                              vertical distance between
                                              the helicopter and station
                                              A.
AL.....................  Feet..............  Measured Takeoff Noise
                                              Path. The distance from
                                              station A to the measured
                                              helicopter position L.
AL<INF>r</INF>....................  Feet..............  Reference Takeoff Noise
                                              Path. The distance from
                                              station A to the reference
                                              helicopter position L<INF>r</INF>.
AM.....................  Feet..............  Measured Flyover Noise
                                              Path. The distance from
                                              station A to the measured
                                              helicopter position M.
AM<INF>r</INF>....................  Feet..............  Reference Flyover Noise
                                              Path. The distance from
                                              station A to helicopter
                                              position M<INF>r</INF> on the
                                              reference flyover flight
                                              path.
AN.....................  Feet..............  Measured Approach Noise
                                              Path. The distance from
                                              station A to the measured
                                              helicopter noise position
                                              N.
AN<INF>r</INF>....................  Feet..............  Reference Approach Noise
                                              Path. The distance from
                                              station A to the reference
                                              helicopter position N<INF>r</INF>.
AS.....................  Feet..............  Measured Approach Minimum
                                              Distance. The distance
                                              from station A to the
                                              position S on the measured
                                              approach flight path.
AS<INF>r</INF>....................  Feet..............  Reference Approach Minimum
                                              Distance. The distance
                                              from station A to the
                                              position S<INF>r</INF> on the
                                              reference approach flight
                                              path.
AT.....................  Feet..............  Measured Takeoff Minimum
                                              Distance. The distance
                                              from station A to the
                                              position T on the measured
                                              takeoff flight path.
AT<INF>r</INF>....................  Feet..............  Reference Takeoff Minimum
                                              Distance. The distance
                                              from station A to the
                                              position T<INF>r</INF> on the
                                              reference takeoff flight
                                              path.
CI.....................  Feet..............  Takeoff Flight Path
                                              Distance. The distance
                                              from position C at which
                                              the helicopter establishes
                                              a constant climb angle on
                                              the takeoff flight path
                                              passing over station A and
                                              continuing to position I
                                              at which the position of
                                              the helicopter need no
                                              longer be recorded.
DJ.....................  Feet..............  Flyover Flight Path
                                              Distance. The distance
                                              from position D at which
                                              the helicopter is
                                              established on the flyover
                                              flight path passing over
                                              station A and continuing
                                              to position J at which the
                                              position of the helicopter
                                              need no longer be
                                              recorded.
EK.....................  Feet..............  Approach Flight Path
                                              Distance. The distance
                                              from position E at which
                                              the helicopter establishes
                                              a constant angle on the
                                              approach flight path
                                              passing over station A and
                                              continuing to position K
                                              at which the position of
                                              the helicopter need no
                                              longer be recorded.
------------------------------------------------------------------------

Section H36.101 Noise certification test and measurement conditions.

(a) General. This section prescribes the conditions under which aircraft noise certification tests must be conducted and the measurement procedures that must be used to measure helicopter noise during each test.

(b) Test site requirements. (1) Tests to show compliance with established helicopter noise certification levels must consist of a series of takeoffs, level flyovers, and approaches during which measurement must be taken at noise measuring stations located at the measuring points prescribed in this section.

(2) Each takeoff test, flyover test, and approach test includes simultaneous measurements at the flight-track noise measuring station vertically below the reference flight path and at two sideline noise measuring stations, one on each side of the reference flight track 492 feet (150m) from, and on a line perpendicular to, the flight track of the noise measuring station.

(3) The difference between the elevation of either sideline noise measuring station may not differ from the flight-track noise measuring station by more than 20 feet.

(4) Each noise measuring station must be surrounded by terrain having no excessive sound absorption characteristics, such as might be caused by thick, matted, or tall grass, shrubs, or wooded areas.

(5) During the period when the takeoff, flyover, or approach noise/time record indicates the noise measurement is within 10 dB of PNLTM, no obstruction that significantly influences the sound field from the aircraft may exist --

(i) For any flight-track or sideline noise measuring station, within a conical space above the measuring position (the point on the ground vertically below the microphone), the cone being defined by an axis normal to the ground and by half-angle 80° from this axis; and

(ii) For any sideline noise measuring station, above the line of sight between the microphone and the helicopter.

(6) If a takeoff or flyover test series is conducted at weights other than the maximum takeoff weight for which noise certification is requested, the following additional requirements apply:

(i) At least one takeoff test must be conducted at a weight at, or above, the maximum certification weight.

(ii) Each test weight must be within +5 percent or −10 percent of the maximum certification weight.

(iii) FAA-approved data must be used to determine the variation of EPNL with weight for takeoff test conditions.

(7) Each approach test must be conducted with the aircraft stabilized and following a 6.0 degree ±0.5 degree approach angle and must meet the requirements of section H36.107 of this part.

(8) If an approach test series is conducted at weights other than the maximum landing weight for which certification is requested, the following additional requirements apply:

(i) At least one approach test must be conducted at a weight at, or above, the maximum landing weight.

(ii) Each test weight must exceed 90 percent of the maximum landing weight.

(iii) FAA-approved data must be used to determine the variation of EPNL with weight for approach test conditions.

(9) Aircraft performance data sufficient to make the corrections required under section H36.205 of this appendix must be recorded at an FAA-approved sampling rate using FAA approved equipment.

(c) Weather restrictions. The tests must be conducted under the following atmospheric conditions:

(1) No rain or other precipitation.

(2) Ambient air temperature between 36 °F and 95 °F (2.2 °C and 35 °C), inclusively, over that portion of the sound propagation path between the aircraft and a point 10 meters above the ground at the noise measuring station. The temperature and relative humidity measured at aircraft altitude and at 10 meters above ground shall be averaged and used to adjust for propagation path absorption.

(3) Relative humidity and ambient temperature over the portion of the sound propagation path between the aircraft and a point 10 meters above the ground at the noise measuring station is such that the sound attenuation in the one-third octave band centered at 8 kHz is not greater than 12 dB/100 meters and the relative humidity is between 20 percent and 95 percent, inclusively.

(4) Wind velocity as measured at 10 meters above ground does not exceed 10 knots (19 km/h) and the crosswind component does not exceed 5 knots (9 km/h). The wind shall be determined using a continuous thirty-second averaging period spanning the 10dB down time interval.

(5) No anomalous wind conditions (including turbulence) which will significantly affect the noise level of the aircraft when the noise is recorded at each noise measuring station.

(6) The wind velocity, temperature, and relative humidity measurements required under the appendix must be measured in the vicinity of noise measuring stations 10 meters above the ground. The location of the meteorological measurements must be approved by the FAA as representative of those atmospheric conditions existing near the surface over the geographical area which aircraft noise measurements are made. In some cases, a fixed meteorological station (such as those found at airports or other facilities) may meet this requirement.

(7) Temperature and relative humidity measurements must be obtained within 25 minutes of each noise test measurement. Meteorological data must be interpolated to actual times of each noise measurement.

(d) Aircraft testing procedures. (1) The aircraft testing procedures and noise measurements must be conducted and processed in a manner which yields the noise evaluation measure designated as Effective Perceived Noise Level (EPNL) in units of EPNdB, as prescribed in appendix B of this part.

(2) The aircraft height and lateral position relative to the centerline of the reference flight-track (which passes through the noise measuring point) must be determined by an FAA approved method which is independent of normal flight instrumentation, such as radar tracking, theodolite triangulation, laser trajectography, or photographic scaling techniques.

(3) The aircraft position along the flight path must be related to the noise recorded at the noise measuring stations by means of synchronizing signals at an approved sampling rate. The position of the aircraft must be recorded relative to the runway during the entire time period in which the recorded signal is within 10 dB of PNLTM. Measuring and sampling equipment must be approved by the FAA.

Section H36.103 Takeoff test conditions.

(a) This section, in addition to the applicable requirements of sections H36.101 and H36.205(b) of this appendix, applies to all takeoff noise tests conducted under this appendix to show compliance with Part 36.

(b) A test series must consist of at least six flights over the flight-track noise measuring station (with simultaneous measurements at all three noise measuring stations) as follows:

(1) An airspeed of either Vy±5 knots or the lowest approved speed ±5 knots for the climb after takeoff, whichever speed is greater, must be established during the horizontal portion of each test flight and maintained during the remainder of the test flight.

(2) The horizontal portion of each test flight must be conducted at an altitude of 65 feet (20 meters) above the ground level at the flight-track noise measuring station.

(3) Upon reaching a point 1,640 feet (500 meters) from the noise measuring station, the helicopter shall be stabilized at:

(i) The torque used to establish the takeoff distance for an ambient temperature at sea level of 25 °C for helicopters for which the determination of takeoff performance is required by airworthiness regulations; or

(ii) The torque corresponding to minimum installed power available for an ambient temperature at sea level of 25° C for all other helicopters.

(4) The helicopter shall be maintained throughout the takeoff reference procedure at:

(i) The speed used ±5 knots to establish takeoff distance for an ambient temperature at sea level of 25° C for helicopters for which the determination of takeoff performance is required by airworthiness regulations; or

(ii) The best rate of climb speed Vy±5 knots, or the lowest approved speed for climb after takeoff, whichever is greater, for an ambient temperature at sea level of 25° C for all other helicopters.

(5) The rotor speed must be stabilized at the normal operating RPM (±1%) during the entire period of the test flight when the measured helicopter noise level is within 10 dB of PNLTM.

(6) The helicopter must pass over the flight-track noise measuring station within ±10° from the zenith.

Section H36.105 Flyover test conditions.

(a) This section, in addition to the applicable requirements of sections H36.101 and H36.205(c) of this appendix, applies to all flyover noise tests conducted under this appendix to show compliance with Part 36.

(b) A test series must consist of at least six flights (three in each direction) over the flight-track noise measuring station (with simultaneous measurements at all three noise measuring stations) --

(1) In level flight;

(2) At a height of 492 feet ±30 feet (150±9 meters) above the ground level at the flight-track noise measuring station; and

(3) Within ±5° from the zenith.

(c) Each flyover noise test must be conducted --

(1) At a speed of 0.9 VH or 0.45 VH+120 km/hr (0.45 VH+65 kt), whichever is less, maintained throughout the measured portion of the flyover;

(2) At rotor speed stabilized at the normal operating rotor RPM (±1 percent); and

(3) With the power stabilized during the period when the measured helicopter noise level is within 10 dB of PNLTM.

(d) The airspeed shall not vary from the reference airspeed by more than ±5 knots (9 km/hr).

Section H36.107 Approach test conditions.

(a) This section, in addition to the requirements of sections H36.101 and H36.205(d) of this appendix, applies to all approach tests conducted under this appendix to show compliance with Part 36.

(b) A test series must consist of at least six flights over the flight-track noise measuring station (with simultaneous measurements at the three noise measuring stations) --

(1) On an approach slope of 6°±0.5°;

(2) At a height of 394±30 feet (120±9 meters) above the ground level at the flight-track noise measuring station;

(3) Within ±10° of the zenith;

(4) At stabilized airspeed equal to the certificated best rate of climb Vy, or the lowest approved speed for approach, whichever is greater, with power stabilized during the approach and over the flight path reference point, and continued to a normal touchdown; and

(5) At rotor speed stabilized at the maximum normal operating rotor RPM (±1 percent).

(c) The airspeed shall not vary from the reference airspeed by more than ±5 knots (±9 km/hr).

Section H36.109 Measurement of helicopter noise received on the ground.

(a) General. (1) The measurements prescribed in this section provide the data needed to determine the one-third octave band noise produced by an aircraft during testing, at specific noise measuring stations, as a function of time.

(2) Sound pressure level data for aircraft noise certification purposes must be obtained with FAA-approved acoustical equipment and measurement practices.

(3) Paragraphs (b), (c), and (d) of this section prescribe the required equipment specifications. Paragraphs (e) and (f) prescribe the calibration and measurement procedures required for each certification test series.

(b) Measurement system. The acoustical measurement system must consist of FAA-approved equipment equivalent to the following:

(1) A microphone system with frequency response and directivity which are compatible with the measurement and analysis system accuracy prescribed in paragraph (c) of this section.

(2) Tripods or similar microphone mountings that minimize interference with the sound energy being measured.

(3) Recording and reproducing equipment, the characteristics, frequency response, and dynamic range of which are compatible with the response and accuracy requirements of paragraph (c) of this section.

(4) Calibrators using sine wave, or pink noise, of known levels. When pink noise (defined in paragraph (e)(1) of this section) is used, the signal must be described in terms of its root-mean-square (rms) value.

(5) Analysis equipment with the response and accuracy which meets or exceeds the requirements of paragraph (d) of this section.

(6) Attenuators used for range changing in sensing, recording, reproducing, or analyzing aircraft sound must be capable of being operated in equal-interval decibel steps with no error between any two settings which exceeds 0.2 dB.

(c) Sensing, recording, and reproducing equipment. (1) The sound produced by the aircraft must be recorded in such a way that the complete information, including time history, is retained. A magnetic tape recorder is acceptable.

(2) The microphone must be a pressure-sensitive capacitive type, or its FAA-approved equivalent, such as a free-field type with incidence corrector.

(i) The variation of microphone and preamplifier system sensitivity within an angle of ±30 degrees of grazing (60-120 degrees from the normal to the diaphragm) must not exceed the following values:

 
------------------------------------------------------------------------
                                                              Change in
                       Frequency (Hz)                        sensitivity
                                                                 (dB)
------------------------------------------------------------------------
45 to 1,120................................................           1
1,120 to 2,240.............................................         1.5
2,240 to 4,500.............................................         2.5
4,500 to 7,100.............................................           4
7,100 to 11,200............................................           5
------------------------------------------------------------------------

With the windscreen in place, the sensitivity variation in the plane of the microphone diaphragm shall not exceed 1.0 dB over the frequency range 45 to 11,200 Hz.

(ii) The overall free-field frequency response at 90 degrees (grazing incidence) of the combined microphone (including incidence corrector, if applicable) preamplifier, and windscreen must be determined by using either (A) an electrostatic calibrator in combination with manufacturer-provided corrections, or (B) an anechoic free-field facility. The calibration unit must include pure tones at each preferred one-third octave frequency from 50 Hz to 10,000 Hz. The frequency response (after corrections based on that determination) must be flat and within the following tolerances: 44-3,549 Hz ±0.25 dB 3,550-7,099 Hz ±0.5 dB 7,100-11,200 Hz ±1.0 dB

(iii) Specifications concerning sensitivity to environmental factors such as temperature, relative humidity, and vibration must be in conformity with the recommendations of International Electrotechnical Commission (IEC) Publication No. 179, entitled "Precision Sound Level Meters", as incorporated by reference under §36.6 of this part.

(iv) If the wind speed exceeds 6 knots, a windscreen must be employed with the microphone during each measurement of aircraft noise. Correction for any insertion loss produced by the windscreen, as a function of frequency, must be applied to the measured data and any correction applied must be reported.

(3) If a magnetic tape recorder is used to store data for subsequent analysis, the record/replay system (including tape) must conform to the following:

(i) The electric background noise produced by the system in each one-third octave must be at least 35 dB below the standard recording level, which is defined as the level that is either 10 dB below the 3 percent harmonic distortion level for direct recording or ±40 percent deviation for frequency modulation (FM) recording.

(ii) At the standard recording level, the corrected frequency response in each selected one-third octave band between 44 Hz and 180 Hz must be flat and within ±0.75 dB, and in each band between 180 Hz and 11,200 Hz must be flat and within ±0.25 dB.

(iii) If the overall system satisfies the requirements of paragraph (c)(2)(ii) of this section, and if the limitations of the dynamic range of the equipment are insufficient to obtain adequate spectral information, high frequency pre-emphasis may be added to the recording channel with the converse de-emphasis on playback. If pre-emphasis is added, the instantaneously recorded sound-pressure level between 800 Hz and 11,200 Hz of the maximum measured noise signal must not vary more than 20 dB between the levels of the maximum and minimum one-third octave bands.

(d) Analysis equipment. (1) A frequency analysis of the acoustic signal must be performed using one-third octave filters which conform to the recommendations of International Electrotechnical Commission (IEC) Publication No. 225, entitled "Octave, Half-Octave, and Third-Octave Band Filters Intended for Analysis of Sound and Vibrations," as incorporated by reference under §36.6 of this part.

(2) A set of 24 consecutive one-third octave filters must be used. The first filter of the set must be centered at a geometric mean frequency of 50 Hz and the last filter at 10,000 Hz. The output of each filter must contain less than 0.5 dB ripple.

(3) The analyzer indicating device may be either analog or digital, or a combination of both. The preferred sequence of signal processing is:

(i) Squaring the one-third octave filter outputs;

(ii) Averaging or integrating; and

(iii) Converting linear formulation to logarithmic.

(4) Each detector must operate over a minimum dynamic range of 60 dB and perform as a root-mean-square device for sinusoidal tone bursts having crest factors of at least 3 over the following dynamic range:

(i) Up to 30 dB below full-scale reading must be accurate within ±0.5 dB;

(ii) Between 30 dB and 40 dB below full-scale reading must be accurate within ±1.0 dB; and

(iii) In excess of 40 dB below full-scale reading must be accurate within ±2.5 dB.

(5) The averaging properties of the integrator must be tested as follows:

(i) White noise must be passed through the 200 Hz one-third octave band filter and the output fed in turn to each detector/integrator. The standard deviation of the measured levels must then be determined from a statistically significant number of samples of the filtered white noise taken at intervals of not less than 5 seconds. The value of the standard deviation must be within the interval 0.48±0.06 dB for a probability limit of 95 percent. An approved equivalent method may be substituted for this test on those analyzers where the test signal cannot readily be fed directly to each detector/integrator.

(ii) For each detector/integrator, the response to a sudden onset or interruption of a constant amplitude sinusoidal signal at the respective one-third octave band center frequency must be measured at sampling times 0.5, 1.0, 1.5, and 2.0 seconds after the onset or interruption. The rising responses must be in the following amounts before the steady-state level:

0.5 seconds, 4.0±1.0 dB

1.0 seconds, 1.75±0.5 dB

1.5 seconds, 1.0±0.5 dB

2.0 seconds, 0.6±0.25 dB

(iii) The falling response must be such that the sum of the decibel readings below the initial steady-state level, and the corresponding rising response reading is         6.5± 1.0 dB, at both 0.5 and 1.0 seconds and, on subsequent records, the sum of the onset plus decay must be greater than 7.5 decibels.

Note 1: For analyzers with linear detection, an approximation of this response would be given by:

 
 
 
SPL (i, k)-10 log  [0.17 (10<SUP>0.1(Li,k-3)</SUP>)
                   +10.21 (0<SUP>0.1(Li,k-2)</SUP>)
                   +0.24 (10<SUP>0.1(Li,k-1)</SUP>)
                   +0.33 (10<SUP>0.1(Li,k)</SUP>)]
 

When this approximation is used, the calibration signal should be established without this weighting.

Note 2: Some analyzers have been shown to have signal sampling rates that are insufficiently accurate to detect signals with crest factor ratios greater than three which is common to helicopter noise. Preferably, such analyzers should not be used for helicopter certification. Use of analysis systems with high signal sampling rates (greater than 40KHz) or those with analog detectors prior to digitization at the output of each one-third octave filter is encouraged.

(iv) Analyzers using true integration cannot meet the requirements of (i), (ii), and (iii) directly, because their overall average time is greater than the sampling interval. For these analyzers, compliance must be demonstrated in terms of the equivalent output of the data processor. Further, in cases where readout and resetting require a dead-time during acquisition, the percentage loss of the total data must not exceed one percent.

(6) The sampling interval between successive readouts shall not exceed 500 milliseconds and its precise value must be known to within ±1 one percent. The instant in time by which a readout is characterized shall be the midpoint of the average period where the averaging period is defined as twice the effective time constant of the analyzer.

(7) The amplitude resolution of the analyzer must be at least 0.25 dB.

(8) After all systematic errors have been eliminated, each output level from the analyzer must be accurate within ±1.0 dB of the level of the input signal. The total systematic errors for each of the output levels must not exceed ±3.0 dB. For contiguous filter systems, the systematic corrections between adjacent one-third octave channels must not exceed 4.0 dB.

(9) The dynamic range capability of the analyzer to display a single aircraft noise event, in terms of the difference between full-scale output level and the maximum noise level of the analyzer equipment, must be at least 60 dB.

(e) Calibrations. (1) Within five days prior to beginning each test series, the complete electronic system, as installed in field including cables, must be electronically calibrated for frequency and amplitude by the use of a pink noise signal of known amplitudes covering the range of signal levels furnished by the microphone. For purposes of this section, "pink noise" means a noise whose noise-power/unit-frequency is inversely proportional to frequency at frequencies within the range of 44 Hz to 11,200 Hz. The signal used must be described in terms of its average root-mean-square (rms) values for a nonoverload signal level. This system calibration must be repeated within five days of the end of each test series, or as required by the FAA.

(2) Immediately before and after each day's testing, a recorded acoustic calibration of the system must be made in the field with an acoustic calibrator to check the system sensitivity and provide an acoustic reference level for the sound level data analysis. The performance of equipment in the system will be considered satisfactory if, during each day's testing, the variation in the calibration value does not exceed 0.5 dB.

(3) A normal incidence pressure calibration of the combined microphone/preamplifier must be performed with pure tones at each preferred one-third octave frequency from 50 Hz to 10,000 Hz. This calibration must be completed within 90 days prior to the beginning of each test series.

(4) Each reel of magnetic tape must:

(i) Be pistonphone calibrated; and

(ii) At its beginning and end, carry a calibration signal consisting of at least a 15 second burst of pink noise, as defined in paragraph (e)(1) of this section.

(5) Data obtained from tape recorded signals are not considered reliable if the difference between the pink noise signal levels, before and after the tests in each one-third octave band, exceeds 0.75 dB.

(6) The one-third octave filters must have been demonstrated to be in conformity with the recommendations of IEC Publication 225 as incorporated by reference under §36.6 of this part, during the six calendar months preceding the beginning of each test series. However, the correction for effective bandwidth relative to the center frequency response may be determined for each filter by:

(i) Measuring the filter response to sinusoidal signals at a minimum of twenty frequencies equally spaced between the two adjacent preferred one-third octave frequencies; or

(ii) Using an FAA approved equivalent technique.

(7) A performance calibration analysis of each piece of calibration equipment, including pistonphones, reference microphones, and voltage insert devices, must have been made during the six calendar months preceding the beginning of each day's test series. Each calibration must be traceable to the National Bureau of Standards.

(f) Noise measurement procedures. (1) Each microphone must be oriented so that the diaphragm is substantially in the plane defined by the flight path of the aircraft and the measuring station. The microphone located at each noise measuring station must be placed so that its sensing element is approximately 4 feet above ground.

(2) Immediately before and immediately after each series of test runs and each day's testing, acoustic calibrations of the system prescribed in this section of this appendix must be recorded in the field to check the acoustic reference level for the analysis of the sound level data. Ambient noise must be recorded for at least 10 seconds and be representative of the acoustical background, including system noise, that exists during the flyover test run. During that recorded period, each component of the system must be set at the gain-levels used for aircraft noise measurement.

(3) The mean background noise spectrum must contain the sound pressure levels, which, in each preferred third octave band in the range of 50 Hz to 10,000 Hz, are the averages of the energy of the sound pressure levels in every preferred third octave. When analyzed in PNL, the resulting mean background noise level must be at least 20 PNdB below the maximum PNL of the helicopter.

(4) Corrections for recorded levels of background noise are allowed, within the limits prescribed in section H36.111(c)(3) of this appendix.

Section H36.111      Reporting and correcting measured data

(a) General. Data representing physical measurements, and corrections to measured data, including corrections to measurements for equipment response deviations, must be recorded in permanent form and appended to the record. Each correction must be reported and is subject to FAA approval. An estimate must be made of each individual error inherent in each of the operations employed in obtaining the final data.

(b) Data reporting. (1) Measured and corrected sound pressure levels must be presented in one-third octave band levels obtained with equipment conforming to the standards prescribed in section H36.109 of this appendix.

(2) The type of equipment used for measurement and analysis of all acoustic, aircraft performance, and meteorological data must be reported.

(3) The atmospheric environmental data required to demonstrate compliance with this appendix, measured throughout the test period, must be reported.

(4) Conditions of local topography, ground cover, or events which may interfere with sound recording must be reported.

(5) The following aircraft information must be reported:

(i) Type, model, and serial numbers, if any, of aircraft engines and rotors.

(ii) Gross dimensions of aircraft and location of engines.

(iii) Aircraft gross weight for each test run.

(iv) Aircraft configuration, including landing gear positions.

(v) Airspeed in knots.

(vi) Helicopter engine performance as determined from aircraft instruments and manufacturer's data.

(vii) Aircraft flight path, above ground level in feet, determined by an FAA approved method which is independent of normal flight instrumentation, such as radar tracking, theodolite triangulation, laser trajectography, or photographic scaling techniques.

(6) Aircraft speed, and position, and engine performance parameters must be recorded at an approved sampling rate sufficient to correct to the noise certification reference test conditions prescribed in section H36.3 of this appendix. Lateral position relative to the reference flight-track must be reported.

(c) Data corrections. (1) Aircraft position, performance data and noise measurement must be corrected to the noise certification reference conditions as prescribed in sections H36.3 and H36.205 of this appendix.

(2) The measured flight path must be corrected by an amount equal to the difference between the applicant's predicted flight path for the certification reference conditions and the measured flight path at the test conditions. Necessary corrections relating to aircraft flight path or performance may be derived from FAA-approved data for the difference between measured and reference engine conditions, together with appropriate allowances for sound attenuation with distance. The Effective Perceived Noise Level (EPNL) correction must be less than 2.0 EPNdB for any combination of the following:

(i) The aircraft's not passing vertically above the measuring station.

(ii) Any difference between the reference flight-track and the actual minimum distance of the aircraft's ILS antenna from the approach measuring station.

(iii) Any difference between the actual approach angle and the noise certification reference approach flight path.

(iv) Any correction of the measured level flyover noise levels which accounts for any difference between the test engine thrust or power and the reference engine thrust or power.

Detailed correction requirements are prescribed in section H36.205 of this appendix.

(3) Aircraft sound pressure levels within the 10 dB-down points must exceed the mean background sound pressure levels determined under section A36.3(f)(3) by at least 5 dB in each one-third octave band or be corrected under an FAA approved method to be included in the computation of the overall noise level of the aircraft. An EPNL may not be computed or reported from data from which more than four one-third octave bands in any spectrum within the 10 dB-down points have been excluded under this paragraph.

(d) Validity of results. (1) The test results must produce three average EPNL values within the 90 percent confidence limits, each value consisting of the arithmetic average of the corrected noise measurements for all valid test runs at the takeoff, level flyovers, and approach conditions. The 90 percent confidence limit applies separately to takeoff, flyover, and approach.

(2) The minimum sample size acceptable for each takeoff, approach, and flyover certification measurements is six. The number of samples must be large enough to establish statistically for each of the three average noise certification levels a 90 percent confidence limit which does not exceed ±1.5 EPNdB. No test result may be omitted from the averaging process, unless otherwise specified by the FAA.

(3) To comply with this appendix, a minimum of six takeoffs, six approaches, and six level flyovers is required. To be counted toward this requirement, each flight event must be validly recorded at all three noise measuring stations.

(4) The approved values of VH and Vy used in calculating test and reference conditions and flight profiles must be reported along with measured and corrected sound pressure levels.

Section H36.113      Atmospheric attenuation of sound.

(a) The values of the one-third octave band spectra measured during helicopter noise certification tests under this appendix must conform, or be corrected, to the reference conditions prescribed in section H36.3(a). Each correction must account for any differences in the atmospheric attenuation of sound between the test-day conditions and the reference-day conditions along the sound propagation path between the aircraft and the microphone. Unless the meteorological conditions are within the test window prescribed in this appendix, the test data are not acceptable.

(b) Attenuation rates. The atmospheric attenuation rates of sound with distance for each one-third octave band from 50 Hz to 10,000 Hz must be determined in accordance with the formulations and tabulations of SAE ARP 866A, entitled "Standard Values of Atmospheric Absorption as a Function of Temperatures and Humidity for Use in Evaluating Aircraft Flyover Noise", as incorporated by reference under §36.6 of this part.

(c) Correction for atmospheric attenuation. (1) EPNL values calculated for measured data must be corrected whenever --

(i) The ambient atmospheric conditions of temperature and relative humidity do not conform to the reference conditions, 77 °F and 70%, respectively, or

(ii) The measured flight paths do not conform to the reference flight paths.

(iii) The temperature and relative humidity measured at aircraft altitude and at 10 meters above the ground shall be averaged and used to adjust for propagation path absorption.

(2) The mean attenuation rate over the complete sound propagation path from the aircraft to the microphone must be computed for each one-third octave band from 50 Hz to 10,000 Hz. These rates must be used in computing the corrections required in section H36.111(d) of this appendix.

PART C -- NOISE EVALUATION AND CALCULATION UNDER §36.803

Section H36.201      Noise Evaluation in EPNdB.

(a) Effective Perceived Noise Level (EPNL), in units of effective perceived noise decibels (EPNdB), shall be used for evaluating noise level values under §36.803 of this part. Except as provided in paragraph (b) of this section, the procedures in appendix B of Part 36 must be used for computing EPNL. appendix B includes requirements governing determination of noise values, including calculations of:

(1) Instantaneous perceived noise levels;

(2) Corrections for spectral irregularities;

(3) Tone corrections;

(4) Duration corrections;

(5) Effective perceived noise levels; and

(6) Mathematical formulation of noy tables.

(b) Notwithstanding the provisions of section B36.5(a), for helicopter noise certification, corrections for spectral irregularities shall start with the corrected sound pressure level in the 50 Hz one-third octave band.

Section H36.203      Calculation of noise levels.

(a) To demonstrate compliance with the noise level limits of section H36.305, the noise values measured simultaneously at the three noise measuring points must be arithmetically averaged to obtain a single EPNdB value for each flight.

(b) The calculated noise level for each noise test series, i.e., takeoff, flyover, or approach must be the numerical average of at least six separate flight EPNdB values. The 90 percent confidence limit for all valid test runs under section H36.111(d) of this appendix applies separately to the EPNdB values for each noise test series.

Section H36.205      Detailed data correction procedures

(a) General. If the test conditions do not conform to those prescribed as noise certification reference conditions under section H36.305 of this appendix, the following correction procedure shall apply:

(1) If a positive value results from any difference between reference and test conditions, an appropriate positive correction must be made to the EPNL calculated from the measured data. Conditions which can result in a positive value include:

(i) Atmospheric absorption of sound under test conditions which is greater than the reference;

(ii) Test flight path at an altitude which is higher than the reference; or

(iii) Test weight which is less than maximum certification weight.

(2) If a negative value results from any difference between reference and test conditions, no correction may be made to the EPNL calculated from the measured data, unless the difference results from:

(i) An atmospheric absorption of sound under test conditions which is less than the reference; or

(ii) A test flight path at an altitude which is lower than the reference.

(3) The following correction procedures may produce one or more possible correction values which must be added algebraically to the calculated EPNL to bring it to reference conditions:

(i) The flight profiles must be determined for both reference and test conditions. The procedures require noise and flight path recording with a synchronized time signal from which the test profile can be delineated, including the aircraft position for which PNLTM is observed at the noise measuring station. For takeoff, the flight profile corrected to reference conditions may be derived from FAA approved manufacturer's data.

(ii) The sound propagation paths to the microphone from the aircraft position corresponding to PNLTM are determined for both the test and reference profiles. The SPL values in the spectrum of PNLTM must then be corrected for the effects of --

(A) Change in atmospheric sound absorption;

(B) Atmospheric sound absorption on the linear difference between the two sound path lengths; and

(C) Inverse square law on the difference in sound propagation path length. The corrected values of SPL are then converted to PNLTM from which PNLTM must be subtracted. The resulting difference represents the correction which must be added algebraically to the EPNL calculated from the measured data.

(iii) The minimum distances from both the test and reference profiles to the noise measuring station must be calculated and used to determine a noise duration correction due to any change in the altitude of aircraft flyover. The duration correction must be added algebraically to the EPNL calculated from the measured data.

(iv) From FAA approved data in the form of curves or tables giving the variation of EPNL with rotor rpm and test speed, corrections are determined and must be added to the EPNL, which is calculated from the measured data to account for noise level changes due to differences between test conditions and reference conditions.

(v) From FAA approved data in the form of curves or tables giving the variation of EPNL with approach angle, corrections are determined and must be added algebraically to the EPNL, which is calculated from measured data, to account for noise level changes due to differences between the 6 degree and the test approach angle.

(b) Takeoff profiles. (1) Figure H1 illustrates a typical takeoff profile, including reference conditions.

(i) The reference takeoff flight path is described in section H36.3(c).

(ii) The test parameters are functions of the helicopter's performance and weight and the atmospheric conditions of temperature, pressure, wind velocity and direction.

(2) For the actual takeoff, the helicopter approaches position C in level flight at 65 feet (20 meters) above ground level at the flight track noise measuring station and at either Vy±5 knots (±9 km/hr) or the maximum speed of the curve tangential at the ordinate of the height-speed envelope plus 3.0 knots (±5 knots), whichever speed is greater. Rotor speed is stabilized at the normal operating RPM (±1 percent), specified in the flight manual. The helicopter is stabilized in level flight at the speed for best rate of climb using minimum engine specifications (power or torque and rpm) along a path starting from a point located 1640 feet (500 meters) forward of the flight-track noise measuring station and 65 feet (20 meters) above the ground. Starting at point B, the helicopter climbs through point C to the end of the noise certification takeoff flight path represented by position I. The position of point C may vary within limits allowed by the FAA. The position of the helicopter shall be recorded for a distance (CI) sufficient to ensure recording of the entire interval during which the measured helicopter noise level is within 10 dB of PNLTM, as required by this rule. Station A is the flight-track noise measuring station. The relationships between the measured and corrected takeoff flight profiles can be used to determine the corrections which must be applied to the EPNL calculated from the measured data.

(3) Figure H1 also illustrates the significant geometrical relationships influencing sound propagation. Position L represents the helicopter location on the measured takeoff flight path from which PNLTM is observed at station A, and Lr is the A and Nρ corresponding position on the reference sound propagation path. AL and ALr both form the angle Φ with their respective flight paths. Position T represents the point on the measured takeoff flight path nearest station A, and Tr is the corresponding position on the reference flight path. The minimum distance to the measured and reference flight paths are indicated by the lines AT and ATr, respectively, which are normal to their flight paths.

(c) Level flyover profiles. (1) The noise type certification level flyover profile is shown in Figure H2. Airspeed must be stabilized within ±5 knots of the reference airspeed given in section H36.3(d). For each run, the difference between airspeed and ground speed shall not exceed 10 knots between the 10 dB down points. Rotor speed must be stabilized at the maximum continuous RPM within one percent, throughout the 10 dB down time period. If the test requirements are otherwise met, flight direction may be reversed for each subsequent flyover, to obtain three test runs in each direction.

View or Download PDF

(2) Figure H2 illustrates comparative flyover profiles when test conditions do not conform to prescribed reference conditions. The position of the helicopter shall be recorded for a distance (DJ) sufficient to ensure recording of the entire interval during which the measured helicopter noise level is within 10 dB of PNLTM, as required. The flyover profile is defined by the height AG which is a function of the operating conditions controlled by the pilot. Position M represents the helicopter location on the measured flyover flight path for which PNLTM is observed at station A, and Mr is the corresponding position on the reference flight path.

(d) Approach profiles. (1) Figure H3 illustrates a typical approach profile, including reference conditions.

(2) The helicopter approaches position H along a 6° (±0.5°) average approach slope throughout the 10 dB down period. The approach procedure shall be acceptable to the FAA and shall be included in the Flight Manual.

(3) Figure H3 illustrates portions of the measured and reference approach flight paths including the significant geometrical relationships influencing sound propagation. EK represents the measured approach path with approach angle η, and Er and Kr represent the reference approach angle of 6°. Position N represents the helicopter location on the measured approach flight path for which PNLTM is observed at station A, and Nr is the corresponding position on the reference approach flight path. The measured and corrected noise propagation paths are AN and ANr, respectively, both of which form the same angle with their flight paths. Position S represents the point on the measured approach flight path nearest station A, and Sr is the corresponding point on the reference approach flight path. The minimum distance to the measured and reference flight paths are indicated by the lines AS and ASr, respectively, which are normal to their flight paths.

View or Download PDF

(e) Correction of noise at source during level flyover. (1) For level overflight, if any combination of the following three factors, 1) airspeed deviation from reference, 2) rotor speed deviation from reference, and 3) temperature deviation from reference, results in an advancing blade tip Mach number which deviates from the reference Mach value, then source noise adjustments shall be determined. This adjustment shall be determined from the manufacturer supplied data approved by the FAA.

(2) Off-reference tip Mach number adjustments shall be based upon a sensitivity curve of PNLTM versus advancing blade tip Mach number, deduced from overflights carried out at different airspeeds around the reference airspeed. If the test aircraft is unable to attain the reference value, then an extrapolation of the sensitivity curve is permitted if data cover at least a range of 0.3 Mach units. The advancing blade tip Mach number shall be computed using true airspeed, onboard outside air temperature, and rotor speed. A separate PNLTM versus advancing blade tip Mach number function shall be derived for each of the three certification microphone locations, i.e., centerline, sideline left, and sideline right. Sideline left and right are defined relative to the direction of the flight on each run. PNLTM adjustments are to be applied to each microphone datum using the appropriate PNLTM function.

(f) PNLT corrections. If the ambient atmospheric conditions of temperature and relative humidity are not those prescribed as reference conditions under this appendix (77 degrees F and 70 percent, respectively), corrections to the EPNL values must be calculated from the measured data under paragraph (a) of this section as follows:

(1) Takeoff flight path. For the takeoff flight path shown in Figure H1, the spectrum of PNLTM observed at station A for the aircraft at position Lr is decomposed into its individual SPLi values.

(i) Step 1. A set of corrected values are then computed as follows:

            SPLic=SPLi+(α i−α io)AL

+(α io)AL−ALr)

+20 log(AL/ALr)

Where SPLi and SPLic are the measured and corrected sound pressure levels, respectively, in the i-th one-third octave band. The first correction term accounts for the effects of change in atmospheric sound absorption where ai and aio are the sound absorption coefficients for the test and reference atmospheric conditions, respectively, for the -ith one-third octave band and Lr A is the measured takeoff sound propagation path. The second correction term accounts for the effects of atmospheric sound absorption on the change in the sound propagation path length where Lr A is the corrected takeoff sound propagation path. The third correction term accounts for the effects of the inverse square law on the change in the sound propagation path length.

(ii) Step 2. The corrected values of the SPLic are then converted to PNLT and a correction term calculated as follows:

Δ1=PNLT−PNLTM

Which represents the correction to be added algebraically to the EPNL calculated from the measured data.

(2) Approach flight path. (i) The procedure described in paragraph (f)(1) of this section for takeoff flight paths is also used for the approach flight path, except that the value for SPLic relate to the approach sound propagation paths shown in Figure H3 as follows:

SPLic=SPLi+(α-α io) AM+

α(AM−AMr)+20 log(AM/AMr)

Where the lines NS and Nr Sr are the measured and referenced approach sound propagation paths, respectively.

(ii) The remainder of the procedure is the same as that prescribed in paragraph (d)(1)(ii) of this section, regarding takeoff flight path.

(3) Sideline microphones. The procedure prescribed in paragraph (f)(1) of this section for takeoff flight paths is also used for the propagation to the sideline microphones, except that the values of SPLic relate only in the measured sideline sound propagation path as follows:

SPLic-SPLi + (α io−α+io)KX

+α io(KX−KXr)+20 log(KX/KXr)

K is the sideline measuring station where

X=L and Xr=Ln for takeoff

X=M and Xr=Mn for approach

X=N and Xr=Nr for flyover

(4) Level flyover flight path. The procedure prescribed in paragraph (f)(1) of this section for takeoff flight paths is also used for the level flyover flight path, except that the values of SPLic relate only to the flyover sound propagation paths as follows:

SPLic=SPLi+(α-α io) AN + α io (AN−ANr)+20 log (AN/ANr)

(g) Duration corrections. (1) If the measured takeoff and approach flight paths do not conform to those prescribed as the corrected and reference flight paths, respectively, under section A36.5(d)(2) it will be necessary to apply duration corrections to the EPNL values calculated from the measured data. Such corrections must be calculated as follows:

(i) Takeoff flight path. For the takeoff flight path shown in Figure H1, the correction term is calculated using the formula --

Δ2=−10 log (AT/ATr) + 10 log (V/Vr)

which represents the correction which must be added algebraically to the EPNL calculated from the measured data. The lengths AT and ATr are the measured and corrected takeoff minimum distances from the noise measuring station A to the measured and the corrected flight paths, respectively. A negative sign indicates that, for the particular case of a duration correction, the EPNL calculated from the measured data must be reduced if the measured flight path is at greater altitude than the corrected flight path.

(ii) Approach flight path. For the approach flight path shown in Figure H3, the correction term is calculated using the formula --

Δ2=−10 log (AS/ASr) + 10 log (V/Vr)

where AS is the measured approach minimum distance from the noise measuring station A to the measured flight path and 394 feet is the minimum distance from station A to the reference flight path.

(iii) Sideline microphones. For the sideline flight path, the correction term is calculated using the formula --

Δ2=−10 log (KX/KXr)+10 log (V/Vr)

K is the sideline measuring station

where X=T and Xr=Tr for takeoff

where X=S and Xr=Sr for approach

where X=G and Xr=Gr for flyover

(iv) Level flyover flight paths. For the level flyover flight path, the correction term is calculated using the formula --

Δ2=−10 log (AG/AGr)+10 log (V/Vr)

where AG is the measured flyover altitude over the noise measuring station A.

(2) The adjustment procedure described in this section shall apply to the sideline microphones in the take-off, overflight, and approach cases. Although the noise emission is strongly dependent on the directivity pattern, variable from one helicopter type to another, the propagation angle &thetas; shall be the same for test and reference flight paths. The elevation angle ψ shall not be constrained but must be determined and reported. The certification authority shall specify the acceptable limitations on ψ. Corrections to data obtained when these limits are exceeded shall be applied using FAA approved procedures.

PART D -- NOISE LIMITS UNDER §36.805

Section H36.301      Noise measurement, evaluation, and calculation

Compliance with this part of this appendix must be shown with noise levels measured, evaluated, and calculated as prescribed under Parts B and C of this appendix.

Section H36.303 [RESERVED]

Section H36.305      Noise levels

(a) Limits. For compliance with this appendix, it must be shown by flight test that the calculated noise levels of the helicopter, at the measuring points described in section H36.305(a) of this appendix, do not exceed the following, with appropriate interpolation between weights:

(1) Stage 1 noise limits for acoustical changes for helicopters are as follows:

(i) For takeoff, flyover, and approach calculated noise levels, the noise levels of each Stage 1 helicopter that exceed the Stage 2 noise limits plus 2 EPNdB may not, after a change in type design, exceed the noise levels created prior to the change in type design.

(ii) For takeoff, flyover, and approach calculated noise levels, the noise levels of each Stage 1 helicopter that do not exceed the Stage 2 noise limits plus 2 EPNdB may not, after the change in type design, exceed the Stage 2 noise limits plus 2 EPNdB.

(2) Stage 2 noise limits are as follows:

(i) For takeoff calculated noise levels -- 109 EPNdB for maximum takeoff weights of 176,370 pounds or more, reduced by 3.01 EPNdB per halving of the weight down to 89 EPNdB for maximum weights of 1,764 pounds or less.

(ii) For flyover calculated noise levels -- 108 EPNdB for maximum weights of 176,370 pounds or more, reduced by 3.01 EPNdB per halving of the weight down to 88 EPNdB for maximum weights of 1,764 pounds or less.

(iii) For approach calculated noise levels -- 110 EPNdB for maximum weights of 176,370 pounds or more, reduced by 3.01 EPNdB per halving of the weight down 90 EPNdB for maximum weight of 1,764 pounds or less.

(b) Tradeoffs. Except to the extent limited under §36.11(b) of this part, the noise limits prescribed in paragraph (a) of this section may be exceeded by one or two of the takeoff, flyover, or approach calculated noise levels determined under section H36.203 of this appendix if

(1) The sum of the exceedances is not greater than 4 EPNdB;

(2) No exceedance is greater than 3 EPNdB; and

(3) The exceedances are completely offset by reduction in the other required calculated noise levels.

J36.1      General.

J36.3      Reference Test Conditions.

J36.5      [Reserved]

J36.101      Noise certification test and measurement conditions.

J36.103      [Reserved]

J36.105      Flyover test conditions.

J36.107      [Reserved]

J36.109      Measurement of helicopter noise received on the ground.

J36.111      Reporting requirements.

J36.113      [Reserved]

J36.201      Noise evaluation in SEL.

J36.203      Calculation of noise levels.

J36.205      Detailed data correction procedures.

J36.301      Noise measurement, evaluation, and calculation.

J36.303      [Reserved]

J36.305      Noise limits.

This appendix prescribes the alternative noise certification requirements identified under §36.1 of this part and subpart H of this part for helicopters in the primary, normal, transport, and restricted categories having maximum certificated takeoff weight of not more than 6,000 pounds including:

(a) The conditions under which an alternative noise certification test under subpart H of this part must be conducted and the alternative measurement procedure that must be used under §36.801 of this part to measure the helicopter noise during the test;

(b) The alternative procedures which must be used under §36.803 of this part to correct the measured data to the reference conditions and to calculate the noise evaluation quantity designated as Sound Exposure Level (SEL); and

(c) The noise limits for which compliance must be shown under §36.805 of this part.

(a) Meteorological conditions. The following are the noise certification reference atmospheric conditions which shall be assumed to exist from the surface to the helicopter altitude:

(1) Sea level pressure of 2116 pounds per square foot (76 centimeters mercury);

(2) Ambient temperature of 77 degrees Fahrenheit (25 degrees Celsius);

(3) Relative humidity of 70 percent; and

(4) Zero wind.

(b) Reference test site. The reference test site is flat and without line-of-sight obstructions across the flight path that encompasses the 10 dB down points of the A-weighted time history.

(c) Level flyover reference profile. The reference flyover profile is a level flight 492 feet (150 meters) above ground level as measured at the noise measuring station. The reference flyover profile has a linear flight track and passes directly over the noise monitoring station. Airspeed is stabilized at 0.9VH; 0.9VNE; 0.45VH + 65 kts (0.45VH + 120 km/h); or 0.45VNE + 65 kts (0.45VNE + 120 km/h), whichever of the four speeds is least. Rotor speed is stabilized at the power on maximum normal operating RPM throughout the 10 dB down time period.

(1) For noise certification purposes, VH is defined as the airspeed in level flight obtained using the minimum specification engine power corresponding to maximum continuous power available for sea level, 77 degree Fahrenheit (25 degrees Celsius) ambient conditions at the relevant maximum certificated weight. The value of VH thus defined must be listed in the Rotorcraft Flight Manual.

(2) VNE is the never-exceed airspeed.

(d) The weight of the helicopter shall be the maximum takeoff weight at which noise certification is requested.

(a) General. This section prescribes the conditions under which helicopter noise certification tests must be conducted and the measurement procedures that must be used to measure helicopter noise during each test.

(b) Test site requirements. (1) The noise measuring station must be surrounded by terrain having no excessive sound absorption characteristics, such as might be caused by thick, matted, or tall grass, shrubs, or wooded areas.

(2) During the period when the flyover noise measurement is within 10 dB of the maximum A-weighted sound level, no obstruction that significantly influences the sound field from the helicopter may exist within a conical space above the noise measuring position (the point on the ground vertically below the microphone), the cone is defined by an axis normal to the ground and by half-angle 80 degrees from this axis.

(c) Weather restrictions. The test must be conducted under the following atmospheric conditions:

(1) No rain or other precipitation;

(2) Ambient air temperature between 36 degrees and 95 degrees Fahrenheit (2 degrees and 35 degrees Celsius), inclusively, and relative humidity between 20 percent and 95 percent inclusively, except that testing may not take place where combinations of temperature and relative humidity result in a rate of atmospheric attenuation greater than 10 dB per 100 meters (30.5 dB per 1000 ft) in the one-third octave band centered at 8 kiloHertz.

(3) Wind velocity that does not exceed 10 knots (19 km/h) and a crosswind component that does not exceed 5 knots (9 km/h). The wind shall be determined using a continuous averaging process of no greater than 30 seconds;

(4) Measurements of ambient temperature, relative humidity, wind speed, and wind direction must be made between 4 feet (1.2 meters) and 33 feet (10 meters) at the noise monitoring station. Unless otherwise approved by the FAA, ambient temperature and relative humidity must be measured at the noise measuring station at the same height above the ground.

(5) No anomalous wind conditions (including turbulence) or other anomalous meteorological conditions that will significantly affect the noise level of the helicopter when the noise is recorded at the noise measuring station; and

(6) The location of the meteorological instruments must be approved by the FAA as representative of those atmospheric conditions existing near the surface over the geographical area where the helicopter noise measurements are made. In some cases, a fixed meteorological station (such as those found at airports or other facilities) may meet this requirement.

(d) Helicopter testing procedures. (1) The helicopter testing procedures and noise measurements must be conducted and processed in a manner which yields the noise evaluation measure designated Sound Exposure Level (SEL) as defined in section J36.109(b) of this appendix.

(2) The helicopter height relative to the noise measurement point sufficient to make corrections required under section J36.205 of this appendix must be determined by an FAA-approved method that is independent of normal flight instrumentation, such as radar tracking, theodolite triangulation, laser trajectography, or photographic scaling techniques.

(3) If an applicant demonstrates that the design characteristics of the helicopter would prevent flight from being conducted in accordance with the reference test conditions prescribed under section J36.3 of this appendix, then with FAA approval, the reference test conditions used under this appendix may vary from the standard reference test conditions, but only to the extent demanded by those design characteristics which make compliance with the reference test conditions impossible.

(a) This section prescribes the flight test conditions and allowable random deviations for flyover noise tests conducted under this appendix.

(b) A test series must consist of at least six flights with equal numbers of flights in opposite directions over the noise measuring station:

(1) In level flight and in cruise configuration;

(2) At a height of 492 feet ±50 feet (150 ±15 meters) above the ground level at the noise measuring station; and

(3) Within ±10 degrees from the zenith.

(c) Each flyover noise test must be conducted:

(1) At the reference airspeed specified in section J36.3(c) of this appendix, with such airspeed adjusted as necessary to produce the same advancing blade tip Mach number as associated with the reference conditions;

(i) Advancing blade tip Mach number (MAT) is defined as the ratio of the arithmetic sum of blade tip rotational speed (VR) and the helicopter true air speed (VT) over the speed of sound (c) at 77 degrees Fahrenheit (1135.6 ft/sec or 346.13 m/sec) such that MAT = (VR + VT)/c; and

(ii) The airspeed shall not vary from the adjusted reference airspeed by more than ±3 knots (±5 km/hr) or an equivalent FAA-approved variation from the reference advancing blade tip Mach number. The adjusted reference airspeed shall be maintained throughout the measured portion of the flyover.

(2) At rotor speed stabilized at the power on maximum normal operating rotor RPM (±1 percent); and

(3) With the power stabilized during the period when the measured helicopter noise level is within 10 dB of the maximum A-weighted sound level (LAMAX).

(d) The helicopter test weight for each flyover test must be within plus 5 percent or minus 10 percent of the maximum takeoff weight for which certification under this part is requested.

(e) The requirements of paragraph (b)(2) of this section notwithstanding, flyovers at an FAA-approved lower height may be used and the results adjusted to the reference measurement point by an FAA-approved method if the ambient noise in the test area, measured in accordance with the requirements prescribed in section J36.109 of this appendix, is found to be within 15 dB(A) of the maximum A-weighted helicopter noise level (LAMAX) measured at the noise measurement station in accordance with section J36.109 of this appendix.

(a) General. (1) The helicopter noise measured under this appendix for noise certification purposes must be obtained with FAA-approved acoustical equipment and measurement practices.

(2) Paragraph (b) of this section identifies and prescribes the specifications for the noise evaluation measurements required under this appendix. Paragraphs (c) and (d) of this section prescribe the required acoustical equipment specifications. Paragraphs (e) and (f) of this section prescribe the calibration and measurement procedures required under this appendix.

(b) Noise unit definition. (1) The value of sound exposure level (SEL, or as denoted by symbol, LAE), is defined as the level, in decibels, of the time integral of squared ‘A'-weighted sound pressure (PA) over a given time period or event, with reference to the square of the standard reference sound pressure (PO) of 20 micropascals and a reference duration of one second.

(2) This unit is defined by the expression: $$

Where TO is the reference integration time of one second and (t2-t1) is the integration time interval.

(3) The integral equation of paragraph (b)(2) of this section can also be expressed as: $$

Where LA(t) is the time varying A-weighted sound level.

(4) The integration time (t2-t1) in practice shall not be less than the time interval during which LA(t) first rises to within 10 dB(A) of its maximum value (LAMAX) and last falls below 10 dB(A) of its maximum value.

(5) The SEL may be approximated by the following expression:

LAE = LAMAX + <delta> A

where <delta> A is the duration allowance given by:

<delta> A = 10 log10 (T)

where T = (t2-t1)/2 and LAMAX is defined as the maximum level, in decibels, of the A-weighted sound pressure (slow response) with reference to the square of the standard reference sound pressure (P0).

(c) Measurement system. The acoustical measurement system must consist of FAA-approved equipment equivalent to the following:

(1) A microphone system with frequency response that is compatible with the measurement and analysis system accuracy prescribed in paragraph (d) of this section;

(2) Tripods or similar microphone mountings that minimize interference with the sound energy being measured;

(3) Recording and reproducing equipment with characteristics, frequency response, and dynamic range that are compatible with the response and accuracy requirements of paragraph (d) of this section; and

(4) Acoustic calibrators using sine wave noise and, if a tape recording system is used, pink noise, of known levels. When pink noise (defined in section H36.109(e)(1) of appendix H of this part) is used, the signal must be described in terms of its root-mean-square (rms) value.

(d) Sensing, recording, and reproducing equipment. (1) The noise levels measured from helicopter flyovers under this appendix may be determined directly by an integrating sound level meter, or the A-weighted sound level time history may be written onto a graphic level recorder set at "slow" response from which the SEL value may be determined. With the approval of the FAA, the noise signal may be tape recorded for subsequent analysis.

(i) The SEL values from each flyover test may be directly determined from an integrating sound level meter complying with the Standards of the International Electrotechnical Commission (IEC) Publication No. 804, "Integrating-averaging Sound Level Meters," as incorporated by reference under §36.6 of this part, for a Type 1 instrument set at "slow" response.

(ii) The acoustic signal from the helicopter, along with the calibration signals specified under paragraph (e) of this section and the background noise signal required under paragraph (f) of this section may be recorded on a magnetic tape recorder for subsequent analysis by an integrating sound level meter identified in paragraph (d)(1)(i) of this section. The record/playback system (including the audio tape) of the tape recorder must conform to the requirements prescribed in section H36.109(c)(3) of appendix H of this part. The tape recorder shall comply with specifications of IEC Publication No. 561, "Electro-acoustical Measuring Equipment for Aircraft Noise Certification," as incorporated by reference under §36.6 of this part.

(iii) The characteristics of the complete system shall comply with the recommendations given in IEC Publication No. 651, "Sound Level Meters," as incorporated by reference under §36.6 of this part, with regard to the specifications concerning microphone, amplifier, and indicating instrument characteristics.

(iv) The response of the complete system to a sensibly plane progressive wave of constant amplitude shall lie within the tolerance limits specified in Table IV and Table V for Type 1 instruments in IEC Publication No. 651, "Sound Level Meters," as incorporated by reference under §36.6 of this part, for weighting curve "A" over the frequency range of 45 Hz to 11500 Hz.

(v) A windscreen must be used with the microphone during each measurement of the helicopter flyover noise. Correction for any insertion loss produced by the windscreen, as a function of the frequency of the acoustic calibration required under paragraph (e) of this section, must be applied to the measured data and any correction applied must be reported.

(e) Calibrations. (1) If the helicopter acoustic signal is tape recorded for subsequent analysis, the measuring system and components of the recording system must be calibrated as prescribed under section H36.109(e) of appendix H of this part.

(2) If the helicopter acoustic signal is directly measured by an integrating sound level meter:

(i) The overall sensitivity of the measuring system shall be checked before and after the series of flyover tests and at intervals (not exceeding one-hour duration) during the flyover tests using an acoustic calibrator using sine wave noise generating a known sound pressure level at a known frequency.

(ii) The performance of equipment in the system will be considered satisfactory if, during each day's testing, the variation in the calibration value does not exceed 0.5 dB. The SEL data collected during the flyover tests shall be adjusted to account for any variation in the calibration value.

(iii) A performance calibration analysis of each piece of calibration equipment, including acoustic calibrators, reference microphones, and voltage insertion devices, must have been made during the six calendar months proceeding the beginning of the helicopter flyover series. Each calibration shall be traceable to the National Institute of Standards and Technology.

(f) Noise measurement procedures. (1) The microphone shall be of the pressure-sensitive capacitive type designed for nearly uniform grazing incidence response. The microphone shall be mounted with the center of the sensing element 4 feet (1.2 meters) above the local ground surface and shall be oriented for grazing incidence such that the sensing element, the diaphragm, is substantially in the plane defined by the nominal flight path of the helicopter and the noise measurement station.

(2) If a tape recorder is used, the frequency response of the electrical system must be determined at a level within 10 dB of the full-scale reading used during the test, utilizing pink or pseudorandom noise.

(3) The ambient noise, including both acoustical background and electrical noise of the measurement systems shall be determined in the test area and the system gain set at levels which will be used for helicopter noise measurements. If helicopter sound levels do not exceed the background sound levels by at least 15 dB(A), flyovers at an FAA-approved lower height may be used and the results adjusted to the reference measurement point by an FAA-approved method.

(4) If an integrating sound level meter is used to measure the helicopter noise, the instrument operator shall monitor the continuous A-weighted (slow response) noise levels throughout each flyover to ensure that the SEL integration process includes, at minimum, all of the noise signal between the maximum A-weighted sound level (LAMAX) and the 10 dB down points in the flyover time history. The instrument operator shall note the actual db(A) levels at the start and stop of the SEL integration interval and document these levels along with the value of LAMAX and the integration interval (in seconds) for inclusion in the noise data submitted as part of the reporting requirements under section J36.111(b) of this appendix.

(a) General. Data representing physical measurements, and corrections to measured data, including corrections to measurements for equipment response deviations, must be recorded in permanent form and appended to the record. Each correction is subject to FAA approval.

(b) Data reporting. After the completion of the test the following data must be included in the test report furnished to the FAA:

(1) Measured and corrected sound levels obtained with equipment conforming to the standards prescribed in section J36.109 of this appendix;

(2) The type of equipment used for measurement and analysis of all acoustic, aircraft performance and flight path, and meteorological data;

(3) The atmospheric environmental data required to demonstrate compliance with this appendix, measured throughout the test period;

(4) Conditions of local topography, ground cover, or events which may interfere with the sound recording;

(5) The following helicopter information:

(i) Type, model, and serial numbers, if any, of helicopter, engine(s) and rotor(s);

(ii) Gross dimensions of helicopter, location of engines, rotors, type of antitorque system, number of blades for each rotor, and reference operating conditions for each engine and rotor;

(iii) Any modifications of non-standard equipment likely to affect the noise characteristics of the helicopter;

(iv) Maximum takeoff weight for which certification under this appendix is requested;

(v) Aircraft configuration, including landing gear positions;

(vi) VH or VNE (whichever is less) and the adjusted reference airspeed;

(vii) Aircraft gross weight for each test run;

(viii) Indicated and true airspeed for each test run;

(ix) Ground speed, if measured, for each run;

(x) Helicopter engine performance as determined from aircraft instruments and manufacturer's data; and

(xi) Aircraft flight path above ground level, referenced to the elevation of the noise measurement station, in feet, determined by an FAA-approved method which is independent of normal flight instrumentation, such as radar tracking, theodolite triangulation, laser trajectography, or photoscaling techniques; and

(6) Helicopter position and performance data required to make the adjustments prescribed under section J36.205 of this appendix and to demonstrate compliance with the performance and position restrictions prescribed under section J36.105 of this appendix must be recorded at an FAA-approved sampling rate.

The noise evaluation measure shall be the sound exposure level (SEL) in units of dB(A) as prescribed under section J36.109(b) of this appendix. The SEL value for each flyover may be directly determined by use of an integrating sound level meter. Specifications for the integrating sound level meter and requirements governing the use of such instrumentation are prescribed under section J36.109 of this appendix.

(a) To demonstrate compliance with the noise level limits specified under section J36.305 of this appendix, the SEL noise levels from each valid flyover, corrected as necessary to reference conditions under section J36.205 of this appendix, must be arithmetically averaged to obtain a single SEL dB(A) mean value for the flyover series. No individual flyover run may be omitted from the averaging process, unless otherwise specified or approved by the FAA.

(b) The minimum sample size acceptable for the helicopter flyover certification measurements is six. The number of samples must be large enough to establish statistically a 90 percent confidence limit that does not exceed ±1.5 dB(A).

(c) All data used and calculations performed under this section, including the calculated 90 percent confidence limits, must be documented and provided under the reporting requirements of section J36.111 of this appendix.

(a) When certification test conditions measured under part B of this appendix differ from the reference test conditions prescribed under section J36.3 of this appendix, appropriate adjustments shall be made to the measured noise data in accordance with the methods set out in paragraphs (b) and (c) of this section. At minimum, appropriate adjustments shall be made for off-reference altitude and for the difference between reference airspeed and adjusted reference airspeed.

(b) The adjustment for off-reference altitude may be approximated from:

<delta>J1=12.5 log10(HT/492) dB;

where <delta>J1 is the quantity in decibels that must be algebraically added to the measured SEL noise level to correct for an off-reference flight path, HT is the height, in feet, of the test helicopter when directly over the noise measurement point, and the constant (12.5) accounts for the effects on spherical spreading and duration from the off-reference altitude.

(c) The adjustment for the difference between reference airspeed and adjusted reference airspeed is calculated from:

<delta>J3=10 log10(VRA/VR) dB;

Where <delta>J3 is the quantity in decibels that must be algebraically added to the measured SEL noise level to correct for the influence of the adjustment of the reference airspeed on the duration of the measured flyover event as perceived at the noise measurement station, VR is the reference airspeed as prescribed under section J36.3.(c) of this appendix, and VRA is the adjusted reference airspeed as prescribed under section J36.105(c) of this appendix.

(d) No correction for source noise during the flyover other than the variation of source noise accounted for by the adjustment of the reference airspeed prescribed for under section J36.105(c) of this appendix need be applied.

(e) No correction for the difference between the reference ground speed and the actual ground speed need be applied.

(f) No correction for off-reference atmospheric attenuation need be applied.

(g) The SEL adjustments must be less than 2.0 dB(A) for differences between test and reference flight procedures prescribed under section J36.105 of this appendix unless a larger adjustment value is approved by the FAA.

(h) All data used and calculations performed under this section must be documented and provided under the reporting requirements specified under section J36.111 of this appendix.

Compliance with this part of this appendix must be shown with noise levels measured, evaluated, and calculated as prescribed under parts B and C of this appendix.

For compliance with this appendix, the calculated noise levels of the helicopter, at the measuring point described in section J36.101 of this appendix, must be shown to not exceed the following (with appropriate interpolation between weights):

(a) For primary, normal, transport, and restricted category helicopters having a maximum certificated takeoff weight of not more than 6,000 pounds and noise tested under this appendix, the Stage 2 noise limit is 82 decibels SEL for helicopters with maximum certificated takeoff weight at which the noise certification is requested, of up to 1,764 pounds and increasing at a rate of 3.01 decibels per doubling of weight thereafter. The limit may be calculated by the equation:

LAE(limit)=82+3.01[log10(MTOW/1764)/log10(2)] dB;

where MTOW is the maximum takeoff weight, in pounds, for which certification under this appendix is requested.

(b) The procedures required in this amendment shall be done in accordance with the International Electrotechnical Commission IEC Publication No. 804, entitled "Integrating-averaging Sound Level Meters," First Edition, dated 1985. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from the Bureau Central de la Commission Electrotechnique Internationale, 1, rue de Varembe, Geneva, Switzerland or the American National Standard Institute, 1430 Broadway, New York City, New York 10018, and can be inspected at the Office of the Federal Register, 800 North Capitol Street NW., suite 700, Washington, DC.