Getting to Grips with Aircraft Noise

Flight Operations Support & Line Assistance
Getting to grips with aircraft noise
TABLE OF CONTENTS
8.5. NADP insertion – NADP function of the FMS 2 (2005 onwards)............................................. 51
8.6. The Airbus Departure Analysis Software (ADAS).................................................................... 52
8.6.1. ADAS inputs........................................................................................................................... 52
8.6.2. ADAS outputs......................................................................................................................... 53
9. A BIT OF THEORY ................................................................................................54
9.1. Phenomenological approach ..................................................................................................... 54
9.1.1. Introduction ............................................................................................................................ 54
9.1.2. Atmospheric absorption ......................................................................................................... 54
9.1.3. Diffraction ............................................................................................................................... 54
9.1.4. Reflection - Refraction ........................................................................................................... 55
9.1.5. Doppler effect......................................................................................................................... 56
9.1.6. Directionality - directivity ........................................................................................................ 57
9.2. Mathematical approach............................................................................................................... 58
9.2.1. Amplitude measure ................................................................................................................ 58
9.2.2. Sound intensity....................................................................................................................... 59
9.3. Psycho-acoustics ........................................................................................................................ 61
9.3.1. Notion of Sound Intensity Level (SIL) .................................................................................... 61
9.3.2. Notion of Sound Pressure Level (SPL).................................................................................. 62
9.3.3. Adding sound pressure levels – notion of masking effect ..................................................... 63
9.3.4. Complex sound signals.......................................................................................................... 64
9.3.5. Aircraft noise description........................................................................................................ 67
9.4. Noise single event description .................................................................................................. 71
9.4.1. Foreword ................................................................................................................................ 71
9.4.2. A- Sound Pressure Level – (ASPL termed LA) ...................................................................... 71
9.4.3. Equivalent A-Sound Pressure Level (EASPL termed LAEQ,T)................................................. 71
9.4.4. Sound Exposure Level (SEL termed LAE) .............................................................................. 71
9.4.5. Single event noise exposure level (SENEL) .......................................................................... 71
9.4.6. SPL, ASPL, EASPL, and SEL representation ....................................................................... 72
9.4.7. Tone Perceived Noise Level (TPNL termed LTPN) ................................................................. 72
9.4.8. Effective Perceived Noise Level (EPNL termed LEPN) ........................................................... 73
9.5. Noise exposure description ....................................................................................................... 74
9.5.1. Introduction ............................................................................................................................ 74
9.5.2. Equivalent Continuous Sound Level (QL termed Leq)............................................................ 74
9.5.3. Time Above threshold (TA) .................................................................................................... 75
9.5.4. Day-Night average sound Level (DNL termed LDN) ............................................................... 75
9.5.5. Community Noise Equivalent Level (CNEL) .......................................................................... 75
9.5.6. Noise and Number Index (NNI termed Lnni) ........................................................................... 76
9.5.7. Weighted equivalent continuous perceived noise level (WECPNL termed LWECPN) .............. 77
9.5.8. Day-Evening-Night Level (LDEN) .......................................................................................... 78
9.5.9. Some indices used in different countries ............................................................................... 79
10. MEASURING NOISE..........................................................................................80
10.1. Introduction.................................................................................................................................. 80
10.2. Microphones ................................................................................................................................ 80
10.3. Analysers ..................................................................................................................................... 81
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