Integrated Noise Model Accuracy for General Aviation Aircraft (2014)

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6 Detailed Analysis–Select Analysis Aircraft The goal of selecting specific aircraft for detailed analysis is to identify those aircraft that if modeled correctly (so that INM computed SEL equals measured SEL), total sound energy for the GA fleet would be sufficiently close to the sound energy that would result if all evaluated aircraft could be correctly modeled. Effect of Correction on Total Sound Energy 6.1 First, separately for departures and arrivals, aircraft types were rank ordered by each one’s total sound energy using their measured SEL values and the total number of operations at VNY.23 Next, total fleet sound energy was computed by summing the energy of all aircraft types, using the modeled SEL and weighting each aircraft type by the annual number of operations at VNY. Finally, starting with the highest total energy aircraft type, we sequentially “corrected” each aircraft type’s SEL and computed the change in total fleet sound energy until all aircraft SEL values matched their measured levels. Note that “correction” means the computation of sound energy was changed from using the modeled SEL to using the measured SEL. Departures 6.2 Figure 5 shows how the total energy was reduced by correcting one aircraft at a time. The aircraft types shown on the horizontal axis are arranged from those with the highest energy contribution (H25B) to those with the lowest energy contribution (C510). The maximum improvement is 2.9 dB if all twenty- nine aircraft could be corrected. The correction to total fleet energy was judged sufficient if the selected aircraft when corrected would provide a result within 0.3 dB of this maximum. The criterion level is shown in Figure 5, and the aircraft selected for detailed analysis are listed in Table 7. The criterion of 0.3 dB from the maximum reduction possible was based on the following reasoning. In modeling, producing results within 0.5 dB of measured levels would normally be considered very accurate (and unusual), and could have served as a reasonable criterion.24 However, since it may not be possible to correct any selected aircraft so that modeling produces exactly measured levels, and since it is apparent that measured levels for a given aircraft type may vary from airport to airport, we tightened the criterion to 0.3 dB – thus increasing the number of the selected aircraft types. 23 Rank orderings differed insignificantly among VNY, HPN and the total for all airports in our database. 24 In modeling annual commercial jet operations, accuracy of modeled results can be ± 2 to ±3 dB of measured DNL and can, with very detailed modeling average within ½ dB across several monitor locations. We have found modeling of commercial jets has been improved considerably over the past decade and is quite accurate, if modeled flight tracks, runway use, etc. are accurate. 31

Figure 5 Effect on total departure fleet sound energy of sequentially correcting each aircraft type, from highest contributor of energy to lowest contributor; the selection criterion is shown Table 7 Aircraft selected for detailed departure analysis, see Figure 5. Designator of Selected Aircraft INM Aircraft Type Measured SEL (dB) Modeled SEL (dB) Measured minus Modeled (dB) Effective Altitude Discrepancy (dB) Discrepancy if Altitude Corrected (dB) H25B* LEAR35* 88.9 94.3 -5.3 -3.14 -8.48 LJ35 LEAR35 86.6 94.1 -7.5 -2.54 -10.06 C560 CNA560E/U 88.8 93.3 -4.5 -2.42 -6.89 GLF4 GIV 87.4 83.5 3.9 -3.47 0.40 LJ45* LEAR35* 85.2 94.2 -9.0 -2.79 -11.75 PRM1* LEAR35* 86.1 93.4 -7.4 -3.08 -10.44 BE40* MU3001* 89.2 93.7 -4.5 -1.76 -6.25 LJ31* LEAR35* 86.1 93.6 -7.5 -2.35 -9.86 F2TH* CL600* 86.8 88.9 -2.1 -2.68 -4.79 F900 F10062 89.9 92.0 -2.2 -2.40 -4.58 32

Arrivals 6.3 Selection of the aircraft types most affecting arrival total energy was accomplished in a manner identical to the selection of departure aircraft, using arrival SEL values and operations numbers. Figure 6 Effect on total arrival sound energy of sequentially correcting each aircraft type, from highest contributor of energy to lowest contributor, and associated selection criterion Table 8 Aircraft selected for detailed arrival analysis, see Figure 6 Designator INM Aircraft Measured SEL (dB) Modeled SEL (dB) Measured minus Modeled (dB) Effective Altitude Discrepancy (dB) Discrepancy if Altitude Corrected (dB) C750* CNA750* 82.3 87.3 -5.0 1.00 -4.04 C56X CNA560XL 85.3 87.8 -2.6 1.01 -1.54 LJ60* CNA55B* 81.6 86.3 -4.7 1.14 -3.54 GLF5 GV 83.0 85.2 -2.2 0.90 -1.28 F900 F10062 83.9 88.1 -4.3 1.51 -2.78 33