The FAA's 65 dB (decibel) Noise "Limit"
About 40 years ago, the FAA set the limit of 65 dBA as "compatible with residential areas."*
When the FAA's 65 db Noise Limit is exceeded, it would be reasonable to believe there would be airport action to reduce the airport noise levels.
The fact is, in 1981, the FAA established 65 decibels ("A") as the guideline at which federal funding is available for soundproofing or other noise mitigation.
FAA noise levels are averaged out over a 24-hour period, including times when aircraft are not in use. One person said, "Dropping a feather on someone's head every minute for one hour, followed by a large brick, would result in the conclusion that, on average, the total impact is equal to dropping a ping pong ball every minute for one hour."
An oversimplified example as we understand it: If one loud plane rumbles overhead daily with 100 dBA sound level readings for 2 minutes, and there were no other aviation noises in that period, the 2 minutes would be divided by the 1440 minutes that are in a day, with a result well under the 65 dBA average limit.
500 flights at 88 dBA averaged over a 24-hour period = 65 dBA
50 flights at 97 dBA averaged over a 24-hour period = 65 dBA
Measuring with a good $2 decibel meter app** for a smart device, it's not uncommon for the often-incessant airport noises heard in our community to be well over 65 dBC; we personally have had a reading of 92 dBC.
If you want to learn more about why airports report lower decibel readings than are actually registered by the human ear.....
The field of measuring decibels is complicated with 2 general categories of measurement.
1) dBA (A-weighted) Used for most noise measuring; underplays both ends of the noise spectrum;
FAA required; understates runway noise*****
2) dBC (C-weighted) Used to measure the entire spectrum, particularly the low sounds of back
blast. These results can be 10 decibels higher than dbA results.
SFO's January 2017 Burlingame Short Term Aircraft Noise Monitoring**** report, page 7, states
"a 2001 study suggested that C-weighting is preferred over A-weighting to describe backblast noise."
Runway monitors measure the decibel levels. The system attempts to attribute any runway noise to specific aircraft. If it can't, the noise is reported as "community", or coming from outside the airport. There is no separate monitoring and reporting of back blast.
In 2016, the FAA conducted a survey of residents around 20 unnamed US airports. The results of this study "should be released by mid-year 2017". We cannot locate any more information about this on the FAA website.
In May, 2015, the FAA announced it "will soon begin work on the next step in a multi-year effort to update the scientific evidence on the relationship between aircraft noise exposure and its effects on communities around airports." We cannot locate any additional information about this on the FAA website.
** Decibel meters or noise meters are in the app store. We use the $2 dB meter pro by Vlad Polyanskiy.
***** We've taken dB readings with the meter set to "A" and then to "B". The "B" readings
match what another dB meter of ours had shown, and that matched with the dB meter
the Noise Abatement Office showed us.
If we set the dB meter to register in "A" readings, the noise levels were 10 decibels lower
than the dB-C readings.
The difference in sound intensity between 60 dB and 70 dB is ten times greater;
from 60 dB to 80 dB it's 100 times greater.
The difference with perceived loudness between 60 dB and 70 dB is two times as loud;
between 60 dB and 80 dB is four times as loud.
Upcoming FAA Airport Noise Reports
December 29, 2020