Aircraft Noise
The noise of aircraft is described in terms of Perceived Noise Levels (PNL), a scale of
noisiness, expressed in pNdB. There is no simple relationship between the dB(A) value
and pNdB value for all noises. However, a useful statement is that, the pNdB value for a
noise is approximately 13 units greater than the dB(A) value for the noise.
A further refinement resulting from the study of aircraft noise is the Effective Noise Level, a
scale of noisiness of a time-varying event, expressed in EPNdB. It is used to describe the
noise of a single aircraft activity. In order to describe the noise exposure associated with
an airport, the EPNdB values are supplemented with such information as the number of
flights of each aircraft type, the flight paths that the aircraft use and the time of day at
which the operations occur. The resulting picture is often presented in such terms as
Noise Exposure Forecast (NEF) contours, which are intended to represent the long-term
average noise exposure in communities around airports. More detailed information on the
subject is available with Ref. 9.