AIRCRAFT NOISE
For many living around airports, noise is the most evident environmental impact of aviation. This briefing examines the sources of noise from airports, the effects of noise on people and the implications of the Government’s forecasts for the growth in aviation. Potential technical and policy options to reduce aircraft noise are outlined. A more detailed POST report is also available covering this and other environmental issues associated with aviation.1
Key points:
· current aircraft noise can affect the quality of life of half a million people living close to UK airports
· increases in air traffic could outstrip technological progress in making individual flights quieter and so worsen the noise climate around many of the UK’s airports over the next 30 years
· as a result, more people could be affected by sleep disturbance, annoyance and possible health effects
· aircraft noise could constrain airport expansion unless substantial noise reductions are made.
The growth of aviation
The Government has forecast that aviation is likely to grow over the next 30 years at an average rate of 4.25% per year. 2 These forecasts are based on unconstrained growth – i.e. that airport and airline capacity is provided to meet all demand. The Department for Transport (DfT) points out that previous mid-range forecasts underestimated demand, with actual demand either following, or even exceeding the ‘high’ forecast growth curve; particularly for forecasts made before the emergence of the low-cost airlines in the late 1990s. 3
To meet the maximum forecast demand for flights, additional airport capacity would be required equivalent to that which can be handled through five new runways – with three of these located in SE England. Spare capacity exists at some airports (particularly at Stansted and Luton at off-peak times) and so some of the forecast growth could be met without the need for additional infrastructure. However, on current policies, spare capacity is likely to be exhausted by 2015, so unless demand were managed or congestion tolerated, meeting the forecast growth to 2030 would require new capacity.
Aircraft noise
Sources
Aircraft landing and taking off are the chief sources of aviation noise. Individual aircraft have become quieter over the past 30 years, but flight frequencies have increased. As a result, aircraft noise is giving rise to increasing community concern. In particular, landing noise is increasing in importance, and has become the dominant reason for complaints at some airports. In addition, those living close to very large airports may experience ‘ground noise’ from sources on the airport such as taxiing aircraft, aircraft engine tests, generators or airside vehicular traffic. Transport links to an airport, particularly private vehicles and trains, can also make a significant contribution to noise around airports.
The box on the next page outlines how aircraft noise is measured. In essence, the DfT estimates current and future impacts of aircraft noise by determining the area exposed to average sound levels of 57dB(A) or more between 7am and 11pm. This measure was chosen as an indicator of the onset of what the government describes as ‘community annoyance’ in the daytime, following a study in 1985 which showed a good correlation of this figure with annoyance. However, it is apparent that the mix and types of aircraft, their frequency of overflight, the social and economic circumstances of affected people and general levels of environmental awareness and sensitivity have changed since the early 1980s. The Government has therefore commissioned a three year study to provide a firmer basis for the relationship between aircraft noise and annoyance. The first results from this new study should be available towards the end of 2004.
postnote June 2003 Number 197 Aircraft noise Page 2
Measuring sound and noise
Environmental noise is measured with reference to the A-weighted decibel scale, dB(A). This reflects the fact that the human ear does not detect all frequencies of sound equally efficiently. To quantify sound levels which vary with time equivalent continuous sound level or Leq is calculated. This indicates the average sound level over a particular time period. For example, an Leq, 24h of 57dB(A) indicates that the sound energy produced by the noise source is equivalent to a constant sound of 57dB(A) over 24 hours. Other measures of noise are also available, that relate to different measurement periods, such as the instantaneous maximum noise level (Lmax), or the average over certain periods, such as evening or night (Lden).
Aircraft noise at airports
The Government considers noise to have the potential for the onset of significant community annoyance above a level of 57dB(A) Leq, but recognises that some people are annoyed at lower levels. Contours of noise from airports are drawn, showing the area exposed to average sound levels of 57dB(A) Leq or more between 7am and 11pm. Contour areas are then compared with population data to determine the number of residents within that contour. Contours are calculated by summing and averaging the noise from arriving and departing aircraft. For example, at Heathrow in 2002, nearly 130 km2 of land from Fulham to Windsor was within the 57dB(A) Leq contour. Calculations of future noise exposure must also take account of the known or planned flight paths to and from the airport and (since different types of aircraft make different amounts of noise) the known or estimated fleet mix at that airport.
Effects
The Government acknowledges that noise can be “one of the most objectionable impacts of airport development.”4 Aircraft noise can affect concentration or sleep and result in feelings of anger, frustration and powerlessness to control the noise. These factors can thus adversely affect people’s quality of life. However, while many express concerns over aircraft noise, there remain considerable uncertainties over the precise nature of its impacts. The box opposite outlines the key effects of aircraft noise. Overall, much of the research in this area is either contradictory or inconclusive and many, including the World Health Organisation have called for considerably more research. Evidence to date suggests that most people exposed to aircraft noise are not adversely affected, but more vulnerable groups may be at increased risk; particularly those with pre-existing sleep problems, stress or mental health problems.
Aircraft noise already has the potential to affect the quality of life of at least half a million people in the UK – with 80% of these living close to major airports in the southeast of England. The figure opposite shows the extent of noise pollution around five major airports in the UK under DfT’s growth forecasts.5 For each situation, under worst-case scenarios, more people are likely to be exposed. Under the central scenarios, increases will be expected at Manchester, Birmingham and Stansted. Reductions at Heathrow and Gatwick would result from technological improvements alongside severely constrained growth.
The effects of aircraft noise Annoyance
Noise can lead to people feeling stressed and angry. It may interfere with conversations and leisure activities in the home, disrupt activities requiring concentration, and discourage people from using outdoor spaces. Further factors may affect whether noise is viewed as ‘annoying’: • occurrence of exposure – noise may be more annoying if it occurs often, even if each noise event is quieter
· fear of accidents – concerns about air crashes may increase some people’s sensitivity to aircraft noise
· fear of the future – especially about future growth in air travel and potential increases in the frequency of flights
· lack of control – inability to alter or escape from the noise source may make it more annoying. 6
The subjective responses to aircraft noise makes it difficult to quantify the relationship between noise and annoyance. However, noise levels below 50dB(A) Leq are unlikely to cause community annoyance while levels of 55dB(A) Leq may severely annoy some people. In the UK, the DfT uses a level of 57dB(A) Leq as an indicator of the onset of community annoyance in daytime. Nevertheless, there are likely to be people exposed to more than 57dB(A) Leq who will not be affected, and also those exposed to lower levels who will be affected. The location of the 57dB(A) contour is therefore not a precise guide (see the box on the next page).
Sleep disturbance
Interference with sleep patterns is frequently reported by those living near airports operating night flights. A recent study of residents in high noise areas close to Heathrow, Gatwick, East Midlands and Coventry airports found between 1 in 5 and 1 in 10 people often reporting difficulty getting to sleep or being woken early . The European Court of Human Rights has ruled that the UK Government’s procedure for decision-making about night flights was flawed, and that this flaw amounted to a “violation of the respect for private and family life and the home” under the European Convention on Human Rights. This judgement did not state that night flights themselves were a violation of human rights. The Government is appealing the decision. In the meantime, night flights continue as before, but if the judgement is upheld, the Government would need to review the regulation and operation of night flights.