What is "epndb"

EPNdB, or Effective Perceived Noise level in decibels, is a measure of the relative loudness of an aircraft pass-by event. It is defined in Annex 16 of the ICAO International Convention on Civil Aviation, and in the US Federal Air Regulations Part 36.

The EPNdB rating of an aircraft is used to estimate how much contribution a given aircraft 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.