In the FAA Reauthorization Act of 2018, Pub. L. 115254, § 188, Congress required the Federal Aviation Administration (“FAA”) to “evaluate alternative noise metrics to current average day-night level standard, such as the use of actual noise sampling to address community airplane noise concerns.” In its April 14, 2020 Report to Congress (“Report”), FAA thumbed its nose at that mandate, and chose instead to enumerate the various available metrics, without any attempt at comparative analysis of their efficacy at representing real world noise impacts when compared to Day/Night Average Sound Level (“DNL”), currently required by FAA for analysis of airport noise impacts.
From FAA’s purely technical perspective, the DNL metric “captures all the acoustic energy within a 24 hour period, adding a 10 dB penalty between the hours of 10 p.m. and 7 a.m. to account for people’s increased sensitivity to noise at night. “ Report, p. 11, § 4.1. What is most notable, however, is what is not said. FAA mentions in passing, but fails to evaluate the comparative benefits of any of the alternative metrics, with the most obvious omission that of the Cumulative Noise Equivalency Level (“CNEL”) metric long used to evaluate aircraft noise in California. That section imposes an additional 5 dB penalty between the hours of 7 p.m. and 10 p.m., hours when families are already at home and particularly sensitive to the noise of overflights. Instead, FAA relentlessly defends DNL, with no attempt to catalogue its failures as, for example, an average of noise created by aircraft operations over a 24 hour period which gives short shrift to the impacts of individual operations, and without the mitigation of the additional 5 dB penalty.
Even more surprising is FAA’s off-hand dismissal of “noise monitoring,” the use of fixed points at which specialized machinery records the noise created by each operation, even though that information is later used to calibrate the noise models’ estimations of which FAA appears to be so fond instead. FAA seeks to justify its own reliance on the mathematical exercise of modelling, by asserting that “real-world situations,” like “monitoring” can include “various sources of error” including non-aircraft sounds. Report, § 7. Ironically, most, if not all large airports have rejected modelling as the exclusive mechanism for determining noise impacts and, instead, utilize complex systems of monitors which record the “real world” incidence of aircraft impacts.
Finally, FAA claims that “rigorous noise measurement procedures are used in the aircraft certification process.” Report, § 2.2. Although not further discussed in its letter, FAA discloses that, in the aircraft certification process, “rigorous noise measurement” (that can only be obtained from monitoring) are used to determine “the maximum noise level that an individual aircraft can emit.” Id. FAA’s logic in verifying the noise of individual operations with independent, individual, noise measurement in the case of aircraft certification, but not where community noise analysis is concerned, remains opaque.
In short, FAA’s mandated “evaluation” of alternative noise metrics has turned into nothing more than an apologia for its own flawed analytic tool. What Congress plans to do with FAA’s letter, demand a supplement or allow it to stand, remains a question. Stay tuned for the answer.