Helicopter noise: Can it be adequately rated?

Abstract

Interest in helicopter noise has increased dramatically over the past few years. The Greater London Council, in connection with a public inquiry into a proposed small heliport in London, issued noise standards for helicopters which they considered would be acceptable for use at this site. These standards were inferred by many to be the requirements for all helicopters suitable for use in London. This is not the case and, of course, the noise standard for other heliport sites would to some extent be dependent on their size and location. Thus, in the opinion of the author, the GLC standard should not be taken as a typical requirement, since in many instances it would be over demanding. Publication of these noise limits, however, had the impact of focusing attention on helicopter noise. The Federal German Republic has recently introduced a law for controlling aircraft noise around airports. Even though this specifically excludes helicopters, the FGR have indicated that the noise standards will be applied to evaluating all sites including heliports/helipads and helicopter operators, both military and civil, will be expected to comply with the requirements. Westland Helicopters Limited have in the past few years been attempting to standardize measurements/flight test procedures for the evaluation of helicopter noise. Close relationships have been established with the Greater London Council and Aerospatiale in France and these have lead to an increased awareness of the problems involved, particularly in rating the actual noise level. More recently the issue of the ANPRM for noise certification of short-haul aircraft, including helicopters, by the FAA has intensified interest. To date methods of assessing helicopter noise have simply been adopted from traffic noise or aircraft noise standards. There are, however, some fundamental aspects associated with helicopter noise which must be taken into consideration, and in this paper the limitation and implication of using conventional methods are discussed. Emphasis is placed on rating helicopter noise in terms of a “single event” and no attempt is made to correlate the findings on a noise zone or ground contour basis. The relative merits of using digital and analogue analysis techniques are also examined.