International Standards Organisation (ISO) agrees measuring methods etc. using international working groups. In the case of aircraft and airfield noise, International Civil Aviation Organisation (ICAO) may put forward standards based upon the ISO-recommended methods of assessment; the ICAO standards could (but not always will) form the basis of individual countries’ standards.
ICAO has developed two methods for certification of take-off noise for individual aircraft types – “Chapter 6”, and “Chapter 10”. The latter is now most commonly used. The noise impact from an aircraft is measured as the total noise effect established on the ground 2.5 kilometres from the rolling point of the aircraft, on the extended centreline of the runway. The level is expressed in the universal “decibels" (dB). It is derived from the sum of the noise energy received over the most noisy 10 seconds from the start of take-off until well past the microphone, rather than the peak noise level. FAI has agreed to support the use of this as an appropriate measure for aircraft certification.
Airfield noise, as experienced at a place such as a nearby house or a measurement spot, is usually expressed in the form of an average, over a certain period of time, for example a 16-hour Leq. It represents the sum of all the noises made by individual aircraft flying past. If the point of measurement were on the ground 2.5 kilometres from the rolling point of the aircraft and on the extended centreline of the runway, a good approximation could be derived from ICAO “Chapter 10” data. That is the method set out in Dr. P. V. Brüel’s 1998-99 paper, “Noise Evaluation of Small Airfields”.
The calculated average is influenced heavily by the noisiest aircraft used, very little by any events 10 dB quieter than that, only moderately by the number of starts of the noisier aircraft, and hardly at all by the number of starts of the quieter aircraft.
The Layman’s guide to the difficult subject of Noise Measurement has been prepared by Mr. Chris J. Nicholas, President of Honour of the FAI Environmental Commission.