Getting to Grips with Aircraft Noise

Recommendations

Info

7 - INFLUENCE FACTORS 40 7. INFLUENCE FACTORS CAUTION: all the charts presented hereafter only illustrate examples of the possible sources of scatter evocated below for a specific case, and as such must not be used for the evaluation of corrections in particular situations. 7.1. BACKGROUND The noise levels computed by the NLC or the NEX are based on the best knowledge we have of the aircraft (flight tests). This knowledge is translated into an engine acoustic model. In addition, both software use models to account for the atmospheric absorption and the lateral attenuation of the sound. The noise levels computed for a procedure assume certain atmospheric conditions, which are likely to differ from the actual conditions (humidity, temperature). • In that context, it is worth noticing that atmospheric conditions influences on the noise atmospheric absorption are shown in ICAO Annex 16 Volume 1 Appendix 1 paragraph 8 – Sound attenuation in air. • The assumed weight of the aircraft is based on the load and trim sheet, and is likely to differ from the actual one. • Neither NLC nor NEX account for the actual topography around the airport when computing the effect of sound waves reflections on the ground. For all these reasons, a certain difference may exist between NLC computations and actual levels as monitored during flight operations, though the deviations are small. Consequently, it is worth mentioning that the confidence to put in these computations stands in the value of the calculated gain between different procedures, rather than into the absolute noise level value itself, which must not be considered as guaranteed. The following charts displays the influence of different parameters on the measured noise levels 6.5 km from brake release point, considering an A320 straight takeoff from sea level. Flight Operations Support & Line Assistance Getting to grips with aircraft noise
7.2. ACTUAL TOW INFLUENCE Flight Operations Support & Line Assistance Getting to grips with aircraft noise 7 - INFLUENCE FACTORS All other parameters being fixed, the actual TOW has got an influence on the noise perceived on ground, through the impact it has on the actual aircraft trajectory. This influence can be considered linear and quite small (around –0.2dB(A) per ton in that case). Do not use for operational purpose 41
Page 1 and 2: Flight Operations Support & Line As
Page 9 and 10: 2.1.2. FAN NOISE Flight Operations
Page 11 and 12: 3.1. ICAO ANNEX 16 VOLUME 1 CHAPTER
Page 17 and 18: 3.2.3.5. RECAPITULATIVE TABLE M= Ma
Page 33 and 34: 6.1.2.2. SIMULATION OF PROCEDURES F
Page 35 and 36: EXAMPLE OF NLC OUTPUT (Point comput
Page 41: Flight Operations Support & Line As
Page 49 and 50: 8.3.2. MCDU PAGES Flight Operations
Page 55 and 56: 8.6.2. ADAS OUTPUTS Flight Operatio
Page 59 and 60: ⎛ dr ⎞ ⎜⎝ c + ⎟⎠ ' dr
Page 63 and 64: 9.3. PSYCHO-ACOUSTICS Flight Operat
Page 69 and 70: 9.3.5. AIRCRAFT NOISE DESCRIPTION F
Page 73 and 74: 9.4. NOISE SINGLE EVENT DESCRIPTION
Page 81 and 82: 9.5.9. SOME INDICES USED IN DIFFERE
Page 83 and 84: 10.3. ANALYSERS Flight Operations S
Page 87: Flight Operations Support & Line As

Getting to Grips with Aircraft Noise

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?