Missed opportunity or necessary avoidance?
Cynthia Schultz, PE
While it would be easy to take the FAA to task for ignoring the congressional mandate, it is not so easy to imagine the outcome of “what ifs” if alternative metrics were explored.
Noise compatibility can be elusive. Airports utilize the Part 150 program to establish the noise impact footprint of the airport and attempt to affect zoning to prevent encroachment of incompatible development in 65 DNL and above contour boundaries. With at time multiple municipalities required to adopt airport protection zones into their local zoning ordinances, airports do not always enjoy the zoning protection as requested. Sound insulation is available to insulate incompatible uses that existed prior to 1981 and can provide for the opportunity for avigation easements but not always. However, the program is limited to the funding available and airports compete aggressively for these funds under the current DNL threshold of significance.
The introduction of performance-based navigation flight procedures through NEXT GEN has consolidated previously dispersed flight tracks over 200 foot corridors dramatically increasing the frequency of operations over a very small areas. This concentration of flight activity and noise has created high levels of annoyance at much lower decibel levels than the FAA predicted. The current significant impact metric, DNL does not provide for adequate analysis of concentrated flight tracks as it represents an average of all flight tracks in all directions to generate a contour that does not provide any indicators of concentrated flight paths over narrow areas.
Without developing a system of compatibility tools from which to utilize alternative metrics to address properties impacted by lower threshold noise levels at a very high frequency of operations, the alternative metrics serve no purpose.
The FAA avoids true engagement on noise impacts other than to employ the Environmental Assessment or Environmental Impact Statement Noise Study that have long been the standard to assess noise impact of proposed changes.
If the FAA were to review and endorse alternative metrics prior to understanding what can be done with them and without knowing if Congress is going to appropriate the funds to provide mitigation based on the alternative metrics then they would be opening pandora’s box.
The answer may lie in rethinking the metroplex approach to reintroduce dispersion below a certain altitude rather than seeking alternative metrics.
By Barbara Lichman ,PHD, JD on June 10, 2020
POSTED IN FEDERAL AVIATION ADMINISTRATION (FAA)
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.
Indeed, stay tuned for the answerS. The right metric is not the only pending question; as explained in the first section of this post, there are more issues with greater consequences that must be decided first:
- The economic and environmental values of NextGen.
- An appropriate assessment of lower threshold noise levels at a very high frequency of operations on defined areas within NextGen’s concentrated noise.
- How to differentiate between the generalized noise examinations of existing Part 150 policy VERSUS specific points which are under the concentrated NextGen flight paths.
- Then to select which select which metrics best determine the concentrated vs. generalized impact.
- Since Congress will adhere to its own budgetary disciplines, which remedies (land acquisition, sound insulation, deviating from NextGen’s preferred track, considering a higher aircraft noise certification, etc.) meet the conjoint goals of efficiency, environment, and safety.
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