Aircraft Noise: FAA Could Improve Outreach Through Enhanced Noise Metrics, Communication, and Support to Communities

GAO-21-103933 Published: Sep 28, 2021. Publicly Released: Sep 28, 2021.
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Fast Facts

Performance-Based Navigation allows for more precise flight paths that reduce flying time, fuel use, and emissions. But for communities under a new path, this may also mean more frequent noise.

FAA combines the intensity and duration of noise and the number of flights overhead on an average day to quantify the noise at locations under a new flight path. We found this approach doesn't provide a clear view of what communities may experience. For example, one loud flight has the same predicted effect as 100 quieter flights.

We recommended FAA supplement its analysis and provide more information to the public about potential flight noise.

View from the ground, looking through the trees, of an airplane flying overhead.

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What GAO Found

The Federal Aviation Administration (FAA) uses established policies to assess potential noise effects of implementing performance-based navigation (PBN) at airports. FAA has been implementing PBN to allow aircraft to fly more precise flight paths intended to reduce flying time, fuel use, and emissions, and PBN may reduce aircraft noise for some communities. FAA uses the Day-Night Average Sound Level (DNL) metric to meet legal requirements in assessing how these more precise flight paths—which can concentrate noise over a smaller area—might affect noise levels at various locations surrounding airports. DNL accounts for the noise intensity, duration, frequency, and time of occurrence for flights above a particular location over an average day.

GAO's analysis showed that because DNL combines the effects of several components of noise into a single metric, it does not provide a clear picture of the flight activity or associated noise levels at a given location. For example, 100 flights per day can yield the same DNL as one flight per day at a higher decibel level, due to the averaging effect of FAA's metric (see figure). GAO's analysis and other research demonstrate the limitations of FAA relying solely on DNL to identify potential noise problems. Also, community concerns about increased noise after PBN implementation, among other factors, have led to legal challenges and delays, reducing the realized benefits of PBN. Since no single metric can convey different noise effects, using additional metrics—such as changes in number of flights overhead—in designing proposed flight paths could help FAA identify and address potential noise concerns.

Examples of Different Flight-Frequency and Sound Exposure Levels Resulting in a Day-Night Average Sound Level (DNL) of 65 decibels (dB)

Examples of Different Flight-Frequency and Sound Exposure Levels Resulting in a Day-Night Average Sound Level (DNL) of 65 decibels (dB)

Over time, FAA has increased its community outreach efforts throughout the PBN implementation process. However, most community stakeholders GAO spoke with said information on potential noise impacts was not clear enough to understand the planned changes. For instance, because FAA's description of the impacts is grounded in DNL, communities may not have the information needed to understand how the number of flights over each location is expected to change. Similar to the use of supplemental metrics in designing a flight path, using them in public outreach may help communities better understand expected noise changes. Furthermore, after implementing PBN, FAA primarily conducts outreach through community forums established to address noise concerns. However, members of some forums GAO spoke with were frustrated and unclear on how to productively engage with FAA to address noise concerns. FAA has some guidance on this process, but it is unclear about the extent to which communities can expect assistance from FAA in proposing changes to flight paths that cause noise concerns. Clearly communicating FAA's expected role in this outreach to the public may help alleviate community frustration.

Why GAO Did This Study

As part of its effort to modernize the National Airspace System, FAA has been implementing new flight paths using satellite-based navigation, called PBN, at airports across the country. GAO reviewed FAA's implementation of PBN with regard to noise and FAA's related public outreach activities.

This report discusses: (1) how FAA assesses potential noise impacts for proposed PBN changes; (2) the extent to which FAA's noise impact analysis conveys expected changes; and (3) FAA's community outreach related to PBN and actions to improve this outreach. GAO reviewed FAA documents and guidance related to PBN implementation and to community outreach and mathematically analyzed how DNL levels reflect changes in noise caused by aircraft overhead. GAO conducted case studies at 13 airports selected to achieve a range of perspectives based on annual operations, the timing of PBN implementation, and geographic location, among other factors. GAO interviewed FAA and local airport officials, industry stakeholders, and community representatives in the selected locations.

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GAO is recommending that FAA (1) identify supplemental noise metrics for use in noise impact analysis for PBN implementation; (2) incorporate additional communication tools, such as supplemental noise metrics, into outreach; and (3) provide information on what the public can expect from FAA in its post-implementation outreach. FAA concurred with the recommendations.


Recommendations for Executive Action

Agency Affected Recommendation Status
Federal Aviation Administration The Administrator of the Federal Aviation Administration should identify appropriate supplemental noise metrics, such as the "number above" metric, and circumstances for their use to aid in FAA's internal assessments of noise impacts related to proposed PBN flight path changes. (Recommendation 1)
As of January 2022, the FAA has said it is conducting a noise policy review and plans to consider whether and under what circumstances supplemental, companion, or alternative noise metrics are appropriate to inform research and policy considerations. FAA plans to complete this review by the end of 2022.
Federal Aviation Administration The Administrator of the Federal Aviation Administration should update guidance to incorporate additional communication tools that more clearly convey expected impacts, such as other noise metrics and visualization tools related to proposed PBN implementation. (Recommendation 2)
As of January 2022, the FAA plans to update guidance on community outreach by the end of 2022.
Federal Aviation Administration The Administrator of the Federal Aviation Administration should, related to post-implementation outreach, provide clearer information to airports and communities on what communities can expect from FAA, including the technical assistance FAA can provide. (Recommendation 3)
As of January 2022, the FAA plans to develop an appropriate process and post-implementation outreach tools by the end of 2022.

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