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35 Version 7.0d [INM version 7.0d (FAA 2013)] was replaced by the Airport Environmental Design Tool (AEDT) Version 2b in May 2015. The helicopter noise modeling methodology in AEDT2b is consistent with INM version 7.0d. Prior to Integrated Noise Model (INM) Version 6, helicopter noise was modeled with Helicopter Noise Model (HNM) (Volpe Transportation Systems Research Center 1994). The heli- copter noise computation model from HNM was incorporated into INM beginning with INM Version 6. FAAâs INM allows users to predict helicopter noise exposure in a range of units (noise metrics). INMâs databases contain information for a variety of helicopter types that include physical descriptions of aircraft; noise-power-distance curves; standard arrival, departure, and level flight profiles; and for some helicopters hover-in-ground-effect profiles, directivity profiles for each operating mode, and spectral class data for some helicopters. The noise power distance curves include A-weighted metrics Maximum Noise Level (Lmax or LAmax) and sound exposure level (SEL), and for some aircraft Tone Corrected Perceived Noise Level (PNLT) and Effective Perceived Noise Level (EPNL). INM uses spectral class data to com- pute C-weighted metrics, C-weighted Maximum Noise Level (LCmax), C-weighted Sound Exposure Level (CEXP), and Time Above C-weighted threshold. Table A1 lists the helicopters that are currently included in the INM database. Note that FAA has published a long list of substitutions for helicopters not included in the database and a recommended helicopter from the database to use as a surrogate for that helicopter. HELICOPTER SPECTRAL CLASSES INM helicopter spectral classes are representations of average spectra for groups of helicopters with com- mon characteristics. Figures A11 and A12 show two of INMâs spectral class charts; for the B212, BO150, and S70 helicopters (Figure A11) and the SA355, S65, and H500D helicopters (Figure A12). Note that the spectral class data are unavailable for frequencies lower than the one-third octave band centered at 50 Hz. The database structure in AEDT2b allows for lower frequency information; however, no data are currently available. Correlations Among Helicopter Noise Metrics A hypothetical helicopter exposure case was constructed to examine the relationships among the noise metrics that INM computes. The purpose of the exercise was to inform the selection of noise metrics for the field measurements of this research project. The numbers and types of measurements required for the social survey and subsequent analyses can directly affect the cost and design of the research. The hypothetical case modeled noise exposure for a generic heliport with a large number of operations. The first case studied featured simple straight-in and straight-out departure flight paths, using the standard profiles built into INM for the nine helicopters that have both A-weighted and PNL-based NPD data. One hundred arrivals and 100 departures were evaluated using an equal distribution of the following helicopter types: B206B3, B407, B427, B429, B430, EC130, R22, R44, and SC300C. Figure A13 shows the 55 through 75 DNL contours for this generic helicopter test case. The grid points shown are 0.1 nautical miles apart (approximately 608 ft). The resulting DNL contours are relatively small, even with 200 daily helicopter operations. Figures A14 and A15 compare the noise metrics that INM can compute relative to the DNL value at each of the grid points within a 4 nautical mile square grid with 0.1 nautical mile spacing. Figure A14 shows the traditional level-based metrics, whereas Figure A15 shows the time above metrics. Table A2 supplies the variance accounted for (coefficients of determination) for each of the noise metrics with DNL. All of the metrics other than the time above metrics are highly correlated with DNL. For all practi- cal purposes, if one of the equivalent energy metrics is known, all of the other equal energy metrics are also known (except for constants and scale factors.) These results are similar to the results for fixed-wing aircraft (Mestre et al. 2011). The R2 values between DNL and individual metrics displayed in Table A2 demonstrate that essentially all of the metrics modeled by INM are highly correlated with DNL. Note that in each case in Table A2 the correlation of determination was based on a linear fit except for the time above metrics. For the time APPENDIX A2 Correlational Analysis of Helicopter Noise Metrics
36 Helicopter INM Name Description A109 Agusta A-109 B206L Bell 206L Long Ranger B212 Bell 212 Huey (UH-1N) (CH-135) B222 Bell 222 B206B3 Bell 206B-3 B407 Bell 407 B427 Bell 427 B429 Bell 429 B430 Bell 430 BO105 BÃ¶lkow BO-105 CH47D Boeing Vertol 234 (CH-47D) EC130 Eurocopter EC-130 w/Arriel 2B1 H500D Hughes 500D MD600N McDonnell Douglas MD-600N w/ RR 250-C47M R22 Robinson R22B w/Lycoming 0320 S61 Sikorsky S-61 (CH-3A) S65 Sikorsky S-65 (CH-53) S70 Sikorsky S-70 Blackhawk (UH-60A) S76 Sikorsky S-76 Spirit SA330J AÃ©rospatiale SA-330J Puma SA341G AÃ©rospatiale SA-341G/342 Gazelle SA350D AÃ©rospatiale SA-350D AStar (AS-350) SA355F AÃ©rospatiale SA-355F Twin Star (AS-355) R44 Robinson R44 Raven / Lycoming O-540-F1B5 SC300C Schweizer 300C / Lycoming HIO-360-D1A SA365N AÃ©rospatiale SA-365N Dauphin (AS-365N) Source: INM 7.0d database, FAA. TABLE A1 HELICOPTERS INCLUDED IN INM V7.0d DATABASE
37 FIGURE A11 Spectral Class Example 1. FIGURE A12 Spectral Class Example 2.
38 FIGURE A13 DNL contours for test case operations. FIGURE A14 Relationship of Traditional Level-Based Noise Metrics to Day-Night Average Noise Level for an example heliport. above metrics a second order polynomial fit was used. The choice of linear or second order fit of DNL to the individual metrics was based on the shape of the data plot and the method that provided the best correlation. TAPNL is the metric most independent from DNL, albeit in a not particularly useful manner. Figure A15 shows that the TAPNL data have a very narrow dynamic range, with a nearly vertical slope between DNL 75 and DNL 80. Time above 95 PNL goes from nearly zero to 1,400 minutes within a range of only Ldn = 5 dB. Note that none of the metrics, the traditional level based metrics or time above metrics, include any corrections or adjustments for impulse type noise that occurs as part of some helicopter operating modes. Note also that the spectral data used by INM to compute C-weighted and PNL metrics do not contain any information below the one-third octave band centered at 50 Hz.
39 FIGURE A15 Correlation of Time Above Metrics to Day-Night Average Noise Level for an example heliport (threshold 65 dB for TALA and TALC and 95 dB TAPNL). Noise Metric R2 Relative to DNL CNEL 0.99997 LAEQ 1 LAEQD 0.99997 LAEQN 0.99997 SEL 0.99998 LAMAX 0.95152 NEF 0.92129 WECPNL 0.92128 EPNL 0.92126 PNLTM 0.92887 CEXP 0.99538 LCMAX 0.95927 TALA 0.86722 TALC 0.86848 TAPNL 0.6641 Source: L&B. TABLE A2 COEFFICIENTS OF DETERMINATION (R2) OF NOISE METRICS WITH DNL