FAA’s Report On Alternatives to the DNL Noise Metric Is Tone Deaf

The below comes from Steve Taber.   Mr. Taber is a highly respected attorney specializing in the aviation world, including time as an attorney for FAA.


I have met with and worked with Steve on aviation issues.  I have a high level of respect for his approach and accomplishments.  Therefore I find the below comments from Steve to be very accurate and therefore, regarding the FAA and their attitude towards Congress and the public to be (as kindly as I can put it) disgraceful.

Please be sure to share with the Congressman and staff and share our view, once again, of the FAA.

Slipped under the door while Congress was in recess, hidden on their webpage as a 2018 Report to Congress, and released on a day that DOT Secretary Chao announced billions of dollars of aid to airports, the Federal Aviation Administration released its overdue Report to Congress in fulfillment of Congress’ directive in Section 188 of the FAA Reauthorization Act of 2018 (Pub.L. 115-254) on April 14, 2020. The full report can be found here: https://bit.ly/2W2F5AC.

Section 188 called on the FAA to evaluate alternative metrics to the DNL system that the FAA has been using for over 40 years, “such as the use of actual noise sampling and other methods, to address community airplane noise concerns…” The Report is a rather thin and perfunctory analysis of noise metrics. And it comes as no surprise that the FAA stands by its use of DNL as its primary metric for noise modeling. The Report concludes that DNL provides the best information for its environmental decision-making because it considers the magnitude, duration, and frequency of the noise events. The FAA does admit that there are “supplemental metrics” that could be used in certain situations in addition to DNL, such as N75 for speech interference, % Awakening for sleep disruption, Leq(8) for learning disruption, and Lmax(C) for rattle caused by low frequencies. However, the Report does not offer any analysis as to how the FAA will decide when “supplemental noise metrics” will be used. Thus, use of “supplemental noise metrics” will be left up to the FAA’s discretion making it difficult if not impossible, for community affected by airplane noise to hold the FAA accountable for the creation of noise in their neighborhoods. In the end, the FAA does not appear to have seriously evaluated any change from the DNL metric. Also missing from the report is any analysis or mention of ISO 1996-1:2016 (“Acoustics – Description measurement and assessment of environmental noise”), an international standard specifically adopted to identify community noise concerns in general, but airplane noise in particular.

FAA also claims that this report is in fulfillment of its obligations under Section 173 of the FAA Reauthorization Act as well, which requires the FAA to “complete the ongoing evaluation of alternative metrics to the current Day Night Level (DNL) 65 standard.” While this seemed to be Congress’ invitation to the FAA to address the threshold of significance from 65 DNL and changing it, the FAA declined to address that subject. Instead, the FAA simply reviews other federal agencies’ use of the DNL model and comments that the FAA’s use is line with the other federal agencies.

The issue with the Report is that the FAA continues to be tone deaf to community noise complaints. The Report reflects the disconnect between the FAA and the communities underneath the FAA’s flight paths. At the root of this disconnect is question: “if DNL is the best noise metric, how come it did not predict the community outrage about the implementation of NextGen flight procedures?”

The Report focuses on DNL’s use in noise modeling. That is, it focuses on DNL’s use in carrying out the FAA’s responsibility under the National Environmental Policy Act and other environmental laws before it undertakes or implements a project. But how the FAA uses the DNL metric does not do a very good job of predicting which communities will be affected by airplane noise or how the communities will react to any increase in airplane noise. For example, in the implementation of NextGen the FAA did not find a significant noise impact in any of the Metroplexes it analyzed. Yet many communities across the nation have complained about the significant increase in noise caused by the implementation of NextGen flight procedures. This is, in part, a function of the fact that once the FAA completes its environmental analysis, the FAA considers its responsibility to the communities on the ground to be complete. There is no legal requirement for the FAA to follow up to ensure that its noise analysis was accurate once the flight procedures have been implemented.

But that is when the “community airplane noise concerns” that were supposed to be addressed by the Report begin. Most communities are not aware of the effects of a change in flight procedures until after the flight procedures are implemented. To address the post-implementation concerns of the communities, the FAA points to its pre-implementation environmental analysis showing that there will be no significant increase in noise. The FAA does not use any noise metrics to confirm whether its predictions in the pre-implementation environmental analysis were accurate or to confirm the effects of the new flight procedures on the communities once they are implemented.

In the final analysis, the Report does the bare minimum to satisfy what the FAA perceived to be its responsibility under Sections 188 and 173, without addressing the underlying question about how noise metrics can be used to assist the FAA in addressing noise complaints by identifying them prior to implementation and resolving them after implementation.

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