Noise has historically been the main environmental issue for people living close to airports. It remains high on the agenda of public concern, with the focus mainly on aircraft operations, though there is also potential for noise disturbance from ground operations and maintenance.
Both the EU and the UK have adopted the International Civil Aviation Organisation’s (ICAO) recommended “Balanced Approach to Airport Noise Management”.
Where a noise problem has been identified at an airport, the Balanced Approach process requires the agreement of a noise objective. Following this, all potential measures to manage noise at the airport must be identified, and a cost benefit analysis to determine the most cost-effective package of measures, carried out.
The Balanced Approach consists of four main elements:
Aircraft noise is generated by a number of different ‘sources’, though the dominant one is still the main engines, on approach airframe noise is now becoming important.
Noise standards for new aircraft types, are established by ICAO, and published in Annex 16 volume 1, one of the technical annexes to the Convention on International Civil Aviation (Chicago, 1944). Noise limits are set at three points; two for take-off (one underneath the flight-path, and one to the side,) and one for approach (underneath), and new aircraft types have to demonstrate that they meet these limits to be allowed to operate. The Annex is split into a number of “Chapters”, which contain appropriate standards for different aircraft types, Chapter 4, is the latest standard for subsonic jets, and came into force for newly certificated types at the beginning of 2006.
Since 1978, total noise from the British Airways fleet has decreased by over 80% despite the significant increase in passengers carried, however, despite enormous investment in reducing the impact of noise, the issue remains active.
Using defined, or 'noise preferential' routes (NPR's) are one way of minimising exposure to noise for people living near airports. Such routes are chosen because they direct aircraft, where possible, over less densely populated areas, such as heath and farmland.
Although originally developed as a procedure for reducing fuel use, Continuous Descent Approach (CDA) is another important tool for reducing the noise of approaching aircraft close to airports. It involves starting a continuous steady descent from 6,000ft, or higher, rather than following a number of short descents to set 'cleared' altitudes and joining the 3° approach glide-slope from below, as is normally required by Air Traffic Control.
The CDA technique results in lower noise levels on the ground through two effects:
Additional noise reductions may be achieved by using a Low Power/Low Drag (LPLD) procedure. In this, the aircraft is flown in a 'clean' condition (i.e. with no flap or wheels deployed) as long as possible, consistent with safety. For some aircraft (Boeing 737's and 747's for example), using less than full flap for landing is also sometimes an option, and this can result in lower noise levels when the aircraft are close to the ground.
Most of the work on CDA has been carried out in the UK, and British Airways have taken an active part in the process, working with the Department for Transport (DfT), the Civil Aviation Authority (CAA), the Heathrow Airport Consultative Committee (HACC) and airports to promote its use. We have also been encouraging its use both at other airports in the UK, and internationally through ICAO.
Land use planning covers a wide range of measures aimed at improving the noise climate around airports. The most effective long-term options include the definition of noise zones in which there are restrictions on residential property development, and these are used widely in Europe. In the UK, PPG 24 (being revised as PPS 24) gives planning guidance where there is likely to be a noise issue, but the ODPM have noted that there is a balance to be made between noise and the pressure for housing development, which severely compromises the effectiveness of this document.
At a number of airports, there are restrictions over and above the noise certification standard, the most common of which are applied at night. An example of this is the Night Restrictions Scheme for the designated London airports.
The Quota Count (QC) system was developed in 1995 by the UK Government to help manage the noise generated by aircraft night operations at the three designated London airports - Gatwick, Heathrow and Stansted.
For this scheme, aircraft are grouped into 'QC' bands dependent on their noise performance measured during certification - the noisier aircraft falling into the higher QC bands. The value of the bands doubles every 3 decibels, to reflect the nature of noise measurement - i.e. a doubling in noise energy for every 3 decibel increase.
Quotas have then been set on number of movements, and the total noise (based on QC totals) allowed, during the 'Night Quota period' (
British Airways aircraft fall into the following categories:
|Aircraft type||QC Departure||QC Arrival|
|Airbus Industrie A319||0.5||0.25*|
|Airbus Industrie A320-111/211||1||0.5|
|Airbus Industrie A320-232||0.5||0.25*|
|Airbus Industrie A321-231||1||0.25*|
|Boeing 767-300 (shorthaul)||1||1|
|Boeing 767-300 (longhaul)||2||1|
* New QC 0.25 group introduced from Winter 2006 (these groups previously QC 0.5)
Additional restrictions have also been placed on operations of aircraft in the QC 8 and 16 bands during the night. In addition, from
The scheme is periodically reviewed, with the restrictions currently in operation being replaced starting with the Winter
Noise is described as Sound Pressure Level (SPL), in units called decibels (dB). Decibels are normally weighted to reflect reaction of the human ear to the 'loudness' of different frequencies, or pitch. This is the 'A'-weighted scale, hence dB(A). Noise is expressed logarithmically, such that doubling of noise energy results in an increase of 3dB, e.g. 80dB + 80dB = 83dB. An increase of 3dB is barely perceptible to the human ear and an increase of 10dB approximates to a perceived doubling of noise level. This means that a large amount of acoustic energy reduction is required to produce a significant perceptible difference in noise.
Single aircraft noise events can be described using a number of related noise metrics. Maximum level (Lmax), Sound Event Level (SEL), and Effective Perceived Noise Level (EPNdB) are the most common metrics. EPNdB incorporates the different frequencies and duration of noise patterns, resulting from various speeds and modes of operation of aircraft. The International Civil Aviation Organisation (ICAO) uses EPNdB in setting noise certification standards.
'Average' aircraft noise exposure is described by the Equivalent Continuous Noise Level (Leq). Leq is calculated by integrating the sound energy from all noise events over a given time period and applying a factor for the number of events. Various related derivatives of this metric are used around the world, and in the UK 'average' daytime noise is expressed by the 16 hour Leq (Leq16h).