Effective perceived noise in decibels (EPNdB) is a measure of the relative loudness of an individual aircraft pass-by event. Separate ratings are stated for takeoff, overflight and landing phases, and represent the integrated sum of loudness over the period within which the noise from the aircraft is within 10 dB of the maximum noise (usually at the point of closest approach.) It is defined in Annex 16 of the Convention on International Civil Aviation and in Part 36 of the US Federal Aviation Regulations. The scaling is such that the EPNdB rating represents the integrated loudness over a ten-second period; EPNdB of 100 dB means that the event has the same integrated loudness as a 100 dB sound lasting ten seconds.
The EPNdB rating of an aircraft is used to estimate how much contribution a given aircraft operation will make to the noise impact of an airport in a community, which is estimated using the day-night average sound level metric.
Detailed information on measurement of aircraft acoustic signature to meet the requirements of Annex 16 is found in ICAO Document 9501 and IEC 61265. Data acquisition in one-third-octave bands is required, followed by processing to yield a logarithmically-scaled value in decibels relative to a sound pressure of 20 micropascals, approximately the threshold of hearing.
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