NOISEblog: Aircraft Noise at Source

The International Civil Aviation Organisation (ICAO) promotes a balanced approach to airport noise management consisting of four principle elements, namely: reduction of noise at source; land-use planning and management; noise abatement operational procedures; and aircraft operation restrictions. Each element represents a method of managing noise that, based on the particulars of a given airport, can be used in combination to manage or reduce aircraft noise. One of the most tangible of these four elements in managing aircraft noise levels is the noise at source (that produced by the aircraft itself). Over the last 30 years significant efforts have been aimed at producing quieter planes and, where other elements of the balanced approach have been exhausted or are not feasible, the continued advancement of aircraft technology, producing ever quieter planes, is often seen as a pre requisite to accommodating increased numbers of aircraft movements.

In the UK, like many other countries, the noise levels of civilian aircraft are classified based on the certification standards adopted by ICAO, the rules for which are set out in Annex 16 to the Convention of International Civil Aviation. So as not to inhibit safety or performance the ICAO standards do to themselves aim to drive legislation, but provide a classification of existing technology which airport operators or government regulators may adopt for implementation of their own environmental policies and practices. As technology has improved new certifications have been developed, such that Annex 16 consists of various chapters each corresponding to different stages of aircraft development. The first standard, Chapter 2, targets aircraft certificated prior to 6 October 1977, Chapter 3 aircraft certified from 6 October 1977 and Chapter 4, the most recent, aircraft certified from 1 January 2006. The ICAO standards are applied when an aircraft design is first approved for operational use and do not prevent the use of existing designs, classified under a different standard, being used for the production of new aircraft. However, where an older aircraft (originally classified under, say, Chapter 3) meets the requirements of a later, more stringent, classification (say Chapter 4) manufactures may opt to re-certificate the aircraft designs.

As mentioned above, Annex 16 standards are not designed to correspond with restrictions on the use of a given aircraft per se; however, they do offer a bench mark where by noisier aircraft can be phased out or restricted - on 01 April 2002 European legislation banned the operation of 'Chapter 2' aircraft to/from all European airports.

Although the different body/engine configurations and different series of the same design of aircraft can make it difficult to differentiate a Chapter 2 aircraft from a Chapter 3 or a Chapter 3 from a Chapter 4, for illustrative purposes below are some examples of aircraft belonging to different chapters:

Chapter 2 Aircraft (no longer in use within Europe): Boeing 737-200 (in production until 1988); 747-100 (the world's first 'jumbo jet', in production until 1986)

Chapter 3 Aircraft (characterised by more modern, quieter, jet aircraft): Boeing 737-300 (in production until 1999); Boeing 737-400 (in production until 2000); Boeing 747-400 (in service since 1989), Boeing 777 (in service since 1995); and Airbus A319 (in service since 1996).

Chapter 4 (at least one third quieter than those currently certified to the Chapter 3 standard, IATA): Airbus A380 (in service since 2007); Boeing 737-600 (in service since 1998).

The ICAO standards represent a useful means of categorizing aircraft (with regard to noise level); however, within each Chapter there is naturally going to be variation between aircraft - a 428 seat 747 'jumbo jet' is significantly more disruptive that an 80 seat Fokker 70, both of which are Chapter 3 aircraft. Indeed, Chapter 3 aircraft that exceed Chapter 3 noise standards but have not yet been reclassified as Chapter 4, may actually be quieter than a Chapter 4 aircraft.

Variation in noise level between different aircraft has important implications for the creation of a noise map based on ground observations. If a continuous series of measurements are taken at a given location, over time the average of those measurements will tend toward the true mean noise level experienced at that location; however, just a single measurement, which might observe a ‘quiet’ or ‘noisy’ aircraft, is prone to be un representative of the typical level of noise.

When considering such a spatially distributed phenomenon as aircraft noise it is not practical to take a continuous series of measurements at all locations. This is especially true in the case with the lhrnoisemap project where data collection is opportunistic, based on volunteered geographical information (VGI). The accuracy of this method must therefore rely either on accommodating this uncertainty or assuming repeated sampling of the same location will occur over time - helping the sample become more representative of the true mean at that location. Although the latter is preferable, to achieve repeated samples comprehensively requires a very large number of observations (together with an according time span), and to a greater or lesser degree methods of accommodating the uncertainty will have to be given consideration.

Even if repeated sampling were comprehensively achieved this makes the additional assumption that these observations are random, namely that the incidence of ‘noisy’ aircraft balances those of ‘quiet’. Rather than aiming to achieve a random sample another approach might aim to sample only a selected class of the total population (i.e. only record the noisy aircraft). Doing so would mean that a resulting visualization would represent only that class of the population rather than the population itself; however, would result in more standardised samples, thus reducing the need for repeated sampling. To facilitate this approach in the final analysis of data volunteers are asked to include the type of aircraft in the description of their sample. Whilst it is not realistic to identify most aircraft types the Boeing ‘jumbo’ 747 represents one that, if visible, is recognisable to many people. In the analysis of the data being able to identify a particular type of aircraft, representative of a single class within the population, will provide a means of performing a more rigorous analysis and possibly a method of validating other results. (As mentioned above, although all 747s operating at Heathrow are classified as Chapter 3 aircraft, it must be acknowledged that different series' of the aircraft produce different levels of noise, relative though to the differences between small aircraft and large aircraft this might be considered negligible)