In particular, the study suggested that the 57dB figure used by Government to represent the onset of significant annoyance is far too high. Based on a similar percentage of people annoyed, a figure closer to 50dB is more appropriate. This means that far more people are currently affected by aircraft noise than the government currently admits, and far more would be affected in the future by an increase in capacity at Heathrow. Also the ‘economic cost’ of noise currently estimated by the government would also be too low.
Furthermore, we have long argued – and the ANASE study has confirmed - that while contours are a useful comparative tool, the reaction to aircraft noise is highly influenced by the number of noise events. So although average noise levels around Heathrow have decreased over time due to improvements in individual aircraft, many residents now feel more annoyed because of the relentless growth in the number of flights. Similarly, although the 57 dBALeq contour associated with mixed mode operations at Heathrow might have a geographical impact not larger than the 127 sq km maximum area, mixed mode would subject communities to continuous aircraft operations throughout the day, which would undoubtedly increase their annoyance. The importance attached by residents to the predictable half day’s respite from aircraft noise provided by runway alternation cannot be stated strongly enough. Self-evidently, with 702,000 movements, disturbance would be even greater.
The CAA’s noise model assumes no increase in the number of people living under Heathrow’s flight paths after 2006, although major housing and population growth is expected in London and the South East over the next 20 years. This would increase the number of people annoyed by noise from Heathrow.
We believe that the noise climate is already deteriorating at Heathrow. A particular weakness of the Leq system is that it is liable to be distorted by individual noisy events such as Concorde flights, and it should be noted that the contour target stipulated in the White Paper is set with reference to a year when Concorde was still flying. By 2004 Concorde had been retired, with the result that some additional ‘head room’ became available in the contour target.
The difference Concorde makes can readily be quantified from DfT data:8 an extra two flights per day extend the area of the 57 dBA Leq by almost 20 km2. Since DfT provide a figure for hypothetical extra Concorde flights, it is equally possible to subtract the effect of these flights and estimate the size of the contour had Concorde not been flying at all. This is shown in Table 1. It provides a measure of the performance of the conventional fleet, and a truer indicator of the noise climate.
Table 1: an estimate of noise contours at Heathrow without Concorde (derived from DfT noise contours)
57 dB Leq (km2)
These figures are approximate, but they are sufficient to illustrate a trend: while the impact of growing numbers of aircraft movements was successfully offset by a hard-and-
8 All Concorde were grounded following a crash in Paris in July 2000. Only test flights occurred in 2001; there were limited commercial flights in 2002 and 2003 but by 2004 the aircraft had been retired. For each of these years a hypothetical contour with 1999 levels of Concorde flights was also published.