Noise has historically been the principal environmental issue for aviation. It remains high on the agenda of public concern.
Noise disturbance is a difficult issue to evaluate as it is open to subjective reactions. Its impact is not a lasting one on the actual environment, but it can have significant adverse effects on people living close to an airport, including: interference with communication, sleep disturbance, annoyance responses, learning acquisition, performance effects and cardiovascular and psycho-physiological effects.
Unless there are very many aircraft following a route, it is widely recognised that aircraft flying at a height of at least 10,000ft above the ground do not usually produce “significant” noise impact. But because of the subjective nature of disturbance and the wide variance of local factors, this is not an absolute rule. It is normal for aircraft noise to be associated with airports, because of the low height involved.
To reach an understanding of average noise levels, noise is usually modelled using computer programmes that simulate aircraft “virtually” following an airports operating procedures, but with suitable variability such as track dispersion to make it more realistic. These models, such as the widely used “International Noise Model”, produce aircraft noise footprints for the number of and type of aircraft using an airport in order to calculate the extent of particular noise levels around the airport. This will assume average weather conditions. These noise “contours” can then be placed on a map to see which communities are subjected to different degrees of average noise levels. But it should be remembered that, as average conditions rarely occur, the noise contours are only indicative of typical noise impact.
The most widely used unit for measuring noise levels is dB(A) - the A-weighted scale in decibels. This unit attempts to reflect human reaction to "loudness".
Other dB based measurement units are uniquely related to aircraft.
The perceived noise (PNdB) and effective perceived noise (EPNdB) scales incorporate the different frequencies and duration of noise patterns, resulting from various speeds and modes of operation of aircraft. There is no agreement, even amongst the experts, on which measurement is the most representative, or the most relevant in a particular situation. However, the International Civil Aviation Organisation (ICAO) uses EPNdB for expressing its noise certification standards.
The European Community proposes “Lden” as the common unit for measuring transport noise. Day-evening-night level (Lden) is based on Leq over a whole day with a penalty of 10 dB(A) for night time noise (22.00-7.00) and an additional penalty of 5 dB(A) for evening noise (i.e. 19.00-23.00).
A guide to noise level
- normal conversation 50 - 60 dB(A)
- a loud radio 65 - 75 dB(A)
- a busy street 78 - 85 dB(A)
- a heavy lorry about 7 metres away 95 - 100 dB(A)
- a pighouse at feeding time 110 dB(A)
- a chain saw 115 - 120 dB(A)
- a jet aircraft taking off 25 metres away 140 dB(A) (unlikely to impact the general public!)
Aircraft noise management
All commercial aircraft must meet the International Civil Aviation Organization's (ICAO's) noise certification standards. These apply to aircraft designs and types when they are first approved for operational use, and they have been progressively tightened since the initial standard was adopted in 1971.
The 33rd ICAO Assembly adopted Resolution A33/7 introducing the concept of a ‘balanced approach’ to noise management, thereby establishing a policy approach to address aircraft noise. The ‘balanced approach’ concept of aircraft noise management comprises four principal elements and requires careful assessment of all different options to mitigate noise, including:
- reduction of aircraft noise at source;
- land-use planning and management measures;
- noise abatement operational procedures; and,
- operating restrictions.
The Balanced Approach has since been incorporated into European Community legislation as Directive EC/2002/30).
Other commonly applied noise management measures include:
- depicting preferred noise routes on a map that avoid residential areas as far as possible;
- avoiding over-flying sensitive sites such as hospitals and schools;
- ensuring that the optimum runway(s) and routes are used as far as conditions allow;
- using continuous descent approaches and departure noise abatement techniques;
- avoiding unnecessary use of auxiliary power units by aircraft on-stand;
- building barriers and engine test-pens to contain and deflect noise;
- towing aircraft instead of using jet engines to taxi;
- limiting night operations;
- limiting the number of operations or the extent of a critical noise contour;
- providing noise insulation for the most severely affected houses;
- applying different operational charges based on the noisiness of the aircraft;
- monitoring individual noise levels and penalising any breach.