Integrated Noise Model Accuracy for General Aviation Aircraft (2014)

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4 Detailed Analyses: Overall Description This section describes the methods used to analyze the measured and modeled SEL values of the aircraft types identified in the previous section. Generally, the analyses focus on the sound levels of the GA jet aircraft operating at the six airports of Table 3. 15 Twelve months of data were used with at least eleven of the twelve months from 2011, depending on airport data availability. Table 3 Airports providing flight tracking and noise monitoring data BED L.G. Hansom Field, MA BWI Baltimore/Washington International Thurgood Marshall Airport, MD DEN Denver International Airport, CO FXE Fort Lauderdale Executive Airport, FL HPN Westchester County Airport, NY VNY Van Nuys Airport, CA Data Base of Measured Jet Aircraft 4.1 The aircraft types analyzed and numbers of data points for each are listed in Table 4. These are the 29 jet aircraft types identified in Section 3.4. Each data point represents a valid match of a measured noise event (SEL) at a monitor with a flight track for the aircraft that flew that track. 15 Propeller aircraft were also analyzed, but found not sufficiently significant to be corrected, see Appendix D, page 55. 21

Table 4 Aircraft types evaluated and numbers of useful associated flight track / SEL data points Order Designator Description INM Aircraft Type Used Number Data Points Arrival Departure 1 H25B* British Aerospace BAe-125-700/800; Hawker 750, 800, 800XP, 900XP LEAR35* 3790 2045 2 BE40* Beechjet/Hawker 400 MU3001* 1812 727 3 FA50* Dassault Falcon 50, Mystère 50 F10062* 373 268 4 C560 Cessna 560 Citation 5/5 Ultra/5 Ultra Encore CNA560E/U 2090 1571 5 GLF4 Gulfstream Aerospace G-1159C Gulfstream 4/4SP/SRA-4 GIV 5618 3804 6 C56X Cessna 560XL Citation Excel CNA560XL 3460 1372 7 LJ45* Learjet 45 LEAR35* 848 434 8 C550 Cessna 550, S550, 552 Citation 2/S2/Bravo CNA500/55B 546 435 9 C525 Cessna 525 Citation Jet, Citation CJ1 CNA525C 501 341 10 C650 Cessna 650 Citation 3/6/7 CIT3 395 275 11 F2TH* Dassault Falcon 2000 CL600* 2300 1133 12 CL60 Canadair CL-600 Challenger 600/601/604 CL600/1 2135 1096 13 LJ35 Learjet 35, 36 LEAR35 2373 1731 14 F900 Dassault Falcon 900, Mystère 900 F10062 349 350 15 GLF5 Gulfstream Aerospace G-1159D Gulfstream 5 GV 2247 1347 16 LJ31* Learjet 31 LEAR35* 310 260 17 PRM1* Hawker Premier 1, 390 LEAR35* 310 301 18 C750* Cessna 750 Citation 10 CNA750* 3642 1853 19 GALX* IAI 1126 Galaxy, Gulfstream 200 CL600* 1636 896 20 C25A* Cessna 525A Citation CJ2 CNA525C* 226 142 21 CL30* Bombardier BD-100 Challenger 300 CL601* 1643 1074 22 C680 Cessna 680 Citation Sovereign CNA680 1901 653 23 ASTR IAI 1125 Astra, Gulfstream 100 IA1125 307 121 24 G150* Gulfstream Aerospace Gulfstream G150 IA1125* 290 202 25 C25B Cessna 525B Citation CJ3 CNA525C 690 267 26 LJ60* Learjet 60 CNA55B* 1184 740 27 C501* Cessna 501 Citation 1SP CNA500* 73 32 28 C510 Cessna 510 Citation Mustang CNA510 349 362 29 EA50 Eclipse 500 ECLIPSE500 204 199 *Aircraft types that have an FAA identified substitution aircraft for INM modeling. For example, the H25B is to be modeled with the INM type LEAR35. Computing Discrepancies 4.2 In analyzing differences between measured and modeled levels, it is not only the discrepancy between these two that has implications for the accuracy of the modeled levels, but also discrepancies in altitude. Analysis of the accuracy of the modeling included combined analysis of these two types of errors. As described in the Research Plan, all analyses are focused on a single “prototypical monitor” location. This approach is used because not all airports will have monitors at identical track distances from the airport, and accuracy of modeling is most important at locations relatively close to the airport in the 22

general area where DNL 65 dB is likely to occur.16 By determining average track distances to DNL 65 dB for the study airports, 12,000 feet from the takeoff end (assumed location of brake-release) of the runway for departures and 9,000 feet from landing threshold for arrivals were selected.17 4.2.1 Sound Exposure Level Discrepancies The SEL discrepancy for an aircraft type is the difference between the energy average measured SEL and the energy average modeled SEL.18 The energy average SEL is the basic metric used to compute DNL, rather than the arithmetic average SEL. For example, a simplified equation for computing DNL is: DNL = 10 × log10× � 10𝑆𝐸𝐿𝑑𝑖10𝐷 𝑖=1 + �10𝑆𝐸𝐿𝑛𝑗+1010𝑁 𝑖=1 � − 49.4 Where: 𝑆𝐸𝐿𝑑𝑖 = the i th daytime (7 a.m. to 10 p.m.) SEL from the ith aircraft flight, 𝑆𝐸𝐿𝑛𝑗= the j th nighttime (10 p.m. to 7 a.m.) SEL from the jth aircraft flight, 49.4 = adjustment to DNL (based on number of seconds in 24 hours), 10𝑆𝐸𝐿𝑖10 = sound “energy” represented by ith SEL. In other words, it is the “energy” based value that determines DNL. An energy average SEL for a collection of n SEL values is: 𝐸𝑛𝑒𝑟𝑔𝑦 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑆𝐸𝐿 = 10 × log10 �1/𝑛�10𝑆𝐸𝐿𝑖10𝑛 𝑖=1 � Hence from the collection of measured SEL the energy average is computed at the prototypical monitor location and similarly the energy average modeled SEL is computed. The difference of measured minus modeled SEL energy average values is the discrepancy. The calculation of the energy average SEL values at the 12,000 and 9,000 foot track distances is accomplished with linear regression of the energy values of the SEL data.19 4.2.2 Altitude Discrepancies From initial comparisons of the modeled altitude profiles with the flight tracking data altitude profiles, it was clear that there were consistent differences. These differences meant the measured and modeled aircraft are at different slant distances from the noise monitors resulting in an additional sound level discrepancy. For each aircraft flight, the difference in slant distance was determined and used as an adjustment to the modeled SEL. For example, if the measured distance of the flight track from the noise monitor were 800 feet, and the modeled profile resulted in a distance of 1200 feet, the modeled SEL 16 DNL 65 dB is the level above which noise sensitive residential areas are considered by FAA to be incompatible with aircraft noise. 17 A slight adjustment in the arrival distance analysis point was necessary to avoid extrapolation of measured results; i.e., a very small percentage of the data points were from monitors at distances less than about 9,000 feet from threshold. 18 Throughout the analyses, the discrepancy equals the measured minus the modeled level so that the sign of the discrepancy is the “correction” to the modeled result needed to make it equal to the measured level. 19 The actual calculation is somewhat more complicated, involving a correction to the linear regression of the SEL values, using a regression of the energies of the residuals. 23

needed an additional increase in level of approximately +2.7 dB.20 Once all SEL values for a given aircraft type were adjusted, then the net effect on the energy average modeled SEL was determined. Measured minus modeled sound exposure levels, the decibel effect of altitude discrepancies, and discrepancies that result if the altitude could be corrected are presented in Section 5. Select Aircraft for Additional Analysis 4.3 In order to most efficiently improve the INM modeling of GA aircraft, rather than identify all aircraft needing correction and recommend methods for correcting them, as in the original scope, we were directed in the telephone conference of March 8, 2012 to consider first the most significant GA jet aircraft, focusing on those at VNY. Additionally, if propeller aircraft noise is not significant, the Panel agreed they could be ignored, hence, they were, but see Appendix D. Selecting the most significant aircraft had two steps: 1) determine the effect of correcting each jet aircraft type sequentially on the total GA jet sound energy; 2) define and use a criterion for identifying only the aircraft types that if corrected will provide significant improvement in the total sound energy. Details of these two steps are discussed in Section 6. 20 The distance correction was computed using the average adjustment for distance assumed by the INM for the GA jets in this study by type of operation – arrival or departure. 24