HC Deb 01 March 1984 vol 55 cc334-5W
Mr. Stephen Ross

asked the Secretary of State for Transport what information he has as to the reduction in noise levels emitted by aircraft using Heathrow airport over the last 10 years.

Mr. Ridley

The best illustration of this is the contraction of the area seriously affected by noise. In 1972 the contour where the noise and number index has the value 35 enclosed an area in which 2.1 million people lived. By 1982 the area was much smaller: the number living within it was just over 1 million. Thirty five NNI has been found to be the value at which reasonable people do not experience annoyance.