Noisy Skies

Defining Noise

February 29, 2024 The Aloft Group Season 1 Episode 4
Defining Noise
Noisy Skies
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Noisy Skies
Defining Noise
Feb 29, 2024 Season 1 Episode 4
The Aloft Group

The FAA is currently reviewing its civil aviation noise policy and this episode explains why that's happening, how to define noise metrics, and why it matters to you. 

Noisy Skies is a periodic podcast. Subscribe or follow on your favorite podcast app to be alerted about our newest episodes! Got questions or comments? Drop us a line at We'd love to hear your feedback.

This episode was written and edited by Carolyn McCulley.
Music by Cast of Characters, Cody Martin, and PALA.

Noisy Skies was selected by Feedspot as one of the Top 100 Aviation Podcasts on the web.

Noisy Skies is brought to you by The Aloft Group. The Aloft Group draws on decades of aviation experience to help communities navigate the complexity of aviation noise. To learn more about how Aloft can help your community, visit and read The Forgotten People in Aviation's Matrix.

Noisy Skies is a production of Citygate Films
© 2024 Citygate Films LLC

Show Notes Transcript

The FAA is currently reviewing its civil aviation noise policy and this episode explains why that's happening, how to define noise metrics, and why it matters to you. 

Noisy Skies is a periodic podcast. Subscribe or follow on your favorite podcast app to be alerted about our newest episodes! Got questions or comments? Drop us a line at We'd love to hear your feedback.

This episode was written and edited by Carolyn McCulley.
Music by Cast of Characters, Cody Martin, and PALA.

Noisy Skies was selected by Feedspot as one of the Top 100 Aviation Podcasts on the web.

Noisy Skies is brought to you by The Aloft Group. The Aloft Group draws on decades of aviation experience to help communities navigate the complexity of aviation noise. To learn more about how Aloft can help your community, visit and read The Forgotten People in Aviation's Matrix.

Noisy Skies is a production of Citygate Films
© 2024 Citygate Films LLC

Noisy Skies Podcast

EP 4: Defining Noise

[00:00:00] Music up

[00:00:05] Carolyn McCulley: In late June 2019, Congressman Jamie Raskin was on the floor of the U.S. House of Representatives to talk about aviation noise in his district and the funding of the FAA Reauthorization Act of 2018. 

[00:00:17] Rep. Jamie Raskin: I rise today to share the frustrations of many of my constituents who are suffering from severe noise pollution caused by the FAA's NextGen program, which has altered flight paths to Reagan National Airport. Montgomery County, Maryland residents who live as much as 20 miles away from the airport have experienced a 300 to 500 percent increase in air traffic over their homes. These flight path changes have significantly disrupted life below with relentless noise pollution.

[00:00:49] Carolyn McCulley: Just a few days earlier, Congressman Raskin and 28 other members of Congress had sent a letter to the head of the nonpartisan Government Accountability Office—usually called the GAO—calling for a review of how the FAA handles the impact of aircraft noise. The letter stated: “We would like the GAO to review how the FAA measures aircraft noise, how it evaluates and mitigates noise impacts, and the extent to which the FAA conducts public outreach and responds to public comments regarding noise impacts.” The letter also specifically requested that the GAO address the following question: “Should the FAA revise its current metrics or develop alternative metrics to the current DNL standard?”

[00:01:34] Rep. Jamie Raskin: It's my hope, Mr. Chairman, that with the $17.7 billion that this bill appropriates to the FAA, the agency will take serious steps towards dramatically reducing the noise pollution in residential areas in my district, in Montgomery County, and throughout the nation.

[00:01:50] Carolyn McCulley: Aviation noise metrics. How to define them. How to measure them. How to respond to them. And why it matters to you. It's all in this episode titled: Defining Noise. I'm Carolyn McCulley and this is the Noisy Skies podcast brought to you by The Aloft Group.

[00:02:14] NextGen changed a lot of things as the FAA modernized the National Airspace System. If NextGen is a new term for you, I encourage you to check out Episode 1 of Noisy Skies where we get into it. Because in this episode, we're going to look back at how the metrics of aviation noise were affected by NextGen's implementation.

[00:02:34] But back to the GAO. It took two more years, but in September 2021, the GAO released that report. Its message was clear in the title: “Aircraft Noise. FAA could improve outreach through enhanced noise metrics, communication, and support to communities.” The report pointed out the problems with the DNL metric that the FAA uses to evaluate noise impacts.

[00:03:01] DNL stands for Day-Night Average Sound Level, and it accounts for the noise intensity, duration, frequency, and time of day for flights above a particular location over a 24-hour period. It's a representational average. The problem, as the GAO reported, is that DNL combines the effects of several components of noise into a single metric. Therefore, it does not provide a clear picture of the flight activity or associated noise levels at a given location.

[00:03:38] For example, 100 flights per day can yield the same DNL as 1 flight per day at a higher decibel level. This is due to the averaging effect of the FAA's metric. Then the GAO's report added a helpful visual to illustrate this problem. It showed that a single plane passing over a specific location just once a day at 114 decibels would be the same DNL 65 metric as 100 flights a day over the same location at 94.4 decibels. Now, that's an ear-popping difference for sure. While I have clocked a few large international jets screaming over me at 93 or 94 decibels as they depart Washington Dulles International Airport, it's not a daily experience. Much less 100 times a day. That would be absolutely intolerable! So, from the perspective of people living on the ground, a 24-hour average is not a helpful metric to understand the impact of daily aviation noise.

[00:04:40] Rep. Rick Larsen: Good morning and welcome to today's aviation subcommittee hearing titled: “Aviation Noise. Measuring Progress in Addressing Community Concerns.” Before I begin today, I want to wish all my colleagues on the subcommittee a happy St. Patrick's Day. 

[00:05:53] Carolyn McCulley: So, by March 2022, the House Aviation Subcommittee held a hearing. It looked at the GAO's report and the implementation of noise provisions from the FAA Reauthorization Act of 2018.

[00:05:06] A side note here, normally, the FAA Reauthorization Act comes due every five years, but the 2023 bill has yet to be passed. Maybe it'll get passed in 2024. But, let's get back to Representative Rick Larson as he opened that St. Patrick's Day meeting in 2022. 

[00:05:26] Rep. Rick Larsen: The subcommittee takes aviation very seriously and is focused on finding meaningful solutions to this persistent issue.

[00:05:33] As Congress prepares for the next FAA Reauthorization, the subcommittee must evaluate how the FAA implemented provisions from the ’18 law and identify ongoing challenges. For instance, there are questions about whether the metrics used by the FAA to measure the impacts of aviation noise accurately portray the effects of noise on communities.

[00:05:52] Carolyn McCulley: If you pay attention to the dialogue around aviation noise, you will hear the aviation industry say that planes have gotten quieter over the years. And they have. And that the number of people exposed to significant levels of aircraft noise has decreased. Here is Kevin Welsh, the FAA's Executive Director of the Office of Environment and Energy, explaining that viewpoint to the Aviation Subcommittee members. 

[00:06:17] Kevin Welsh (FAA): Since the ’70s, the number of people living in areas exposed to significant levels of aircraft noise declined from 7 million to around 450,000 in 2019. At the same time, the number of passengers increased from 200 million per year to one billion, nearly one billion per year. So we've seen an overall reduction in noise contrasted with a steady growth in air traffic and passengers.

[00:06:41] Carolyn McCulley: But then you get a report like the GAO's that simply says, as the FAA took action with NextGen, the complaints increased. So … is this then FAA math?! Well, the author of the GAO report, Heather Krause, provided some context at this hearing. 

[00:06:59] Heather Krause (GAO): Despite trends towards quieter airplanes and fewer people exposed to noise, community concerns about noise have persisted. In particular, FAA has been changing flight paths around airports as part of its efforts to modernize the air traffic control system with performance based navigation, or PBN. PBN allows for more precise flight paths that reduce flying time, fuel use, and emissions. Because of these new and more precise routes, noise is likely to be concentrated over a smaller area, meaning that while fewer people experience increases in noise, people directly under PBN routes may have more persistent noise. Affected communities and members of Congress have raised concerns about FAA's implementation of PBN, including whether it provided timely and adequate information about potential noise effects to the public. 

[00:07:49] Carolyn McCulley: A few minutes later, the FAA's Kevin Welsh responded to that concern about noise metrics. 

[00:07:54] Kevin Welsh (FAA): Yes, and actually really agree with the comments that my colleague from GAO just made because, number one, we currently today can use supplemental metrics and do, and number two, as we've talked about today, the increased concentration and number of flights has sort of changed the noise experience.

[00:08:13] So something like the number of flights above in a given period of time may be a really important supplemental metric. But I think most important is to underscore that all of these metrics have trade-offs. The current DNL metric absolutely has trade-offs, but the other metrics do as well. So, in our current Noise Policy Review, these are the types of things that we're looking at to make a recommendation on how to proceed. 

[00:08:37] Carolyn McCulley: But some of the committee members were skeptical of those numbers, including representative Stephen Lynch of Massachusetts. 

[00:08:44] Rep. Stephen Lynch: Mr. Welch, let me just say, it is hard to reconcile your testimony with the testimony of Ms. Krause, and I, I tend to believe her. As you know, I represent a big part of the city of Boston and 21 towns and two other cities, Brockton and Quincy, in the 8th Congressional District in Massachusetts. And we have a hellacious problem with aircraft noise in my district. And I find it hard to believe that only 450,000 people across the country have been complaining about aircraft noise.

[00:09:17] I think I've got that many in my own district just based on the calls I get and the calls that go into Logan Airport. And I just want to say in terms of your outreach program, with all due respect, the last FAA meeting that the FAA agreed to do in my community, my district, we had about 800 people show up very angry about the non-responsiveness of the FAA.

[00:09:42] So I don't want to be rude, but you got a lot of work to do in terms of doing real outreach and real listening to the people that we all work for. And that's, that's the truth. 

[00:09:55] Carolyn McCulley: After adding a few more details about his district, Representative Lynch then concluded with a rebuke. 

[00:10:02] Rep. Stephen Lynch: We all work for these people, the public. You know, the FAA has been one of the most unresponsive public agencies that I deal with and that my constituents deal with. And that's not a, not a good reputation for the FAA to have. You got to do better.

[00:10:25] Carolyn McCulley: So why does the FAA maintain that fewer people now are exposed to significant noise levels than in the past? It's due to how noise was once measured decades ago. A tool that current science shows may be underestimating the actual impact of aviation noise. As we explored in Episode 3, the FAA primarily thinks of the impact of noise in terms of annoyance, but not exclusively.

[00:10:51] And to be fair, the FAA is funding research on the health impacts of noise, while the EPA's noise office sits unfunded. So, the FAA is not totally ignoring this impact. But the tool that undergirds their current metrics may be why the gap exists between the FAA's claims about the number of people affected by noise and what the representatives in this subcommittee meeting were hearing from their constituents.

[00:11:18] As the GAO report summarized 50 years ago back in 1974, the U. S. Environmental Protection Agency identified DNL as the best metric to describe the effects of environmental noise in a simple, uniform, and appropriate way. The metric was then adopted by FAA in 1981 in response to a requirement in the Aviation Safety and Noise Abatement Act of 1979 to establish a single system of measuring noise.

[00:11:50] Within that system, the FAA selected DNL 65 dBA as the appropriate threshold for noise mitigation for residential areas, areas where the noise is incompatible with residential living. Now, this is where I need to pause and point out that there are actually several different decibel scales. Decibels are usually referenced as dB, and in this case, the FAA selected the scale called dBA.

[00:12:17] That A weighted scale accounts for the differences in how people respond to sound and provides a more useful way to evaluate the effect of noise exposure on humans by focusing on those parts of the frequency spectrum that humans hear the most. Got it? But for the sake of simplicity, I will just use the term decibels in this episode.

[00:12:43] So why was DNL 65 selected as the level that was incompatible for residential living? Well, it was based on a noise dose-response curve developed in the 1970s called the Schultz curve. That curve measured the relationship between annoyance and noise exposure. But the problem was that the Schultz curve measured all transportation noise, not just aviation noise.

[00:13:08] Though the Schultz curve was later updated in 1992, a more current and aviation-specific curve was still needed. So the FAA created a new dose-response curve called the National Curve. It was based on a 2021 survey that they conducted called the Neighborhood Environmental Survey and that survey included responses from more than 10,000 people living near 20 representative airports.

[00:13:34] And what happened? A huge shift in the annoyance reported by aviation noise. The old 1992 Schultz curve reported that a little over 12 percent of people were highly annoyed at DNL 65. Years later, in 2021, that number soared to 60 to 70%. In fact, even those living in the lower DNL 50 areas were negatively affected—15 to 23 percent of people living in DNL 50 were highly annoyed by aviation noise, a much higher percentage than even the highest noise levels in the old Schultz curve. So in the spring of 2023, the FAA kicked off its Noise Policy Review. 

[00:14:19] Don Scata (FAA): Welcome to our Noise Policy Review webinar. Thank you for joining us today.My name is Don Scata, and I manage the Noise Division in FAA's Office of Environment and Energy. 

[00:14:29] Carolyn McCulley: The FAA held four webinars to support its Federal Register Notice soliciting feedback from people across the nation about its noise policy and metrics. 

[00:14:39] Don Scata (FAA): In light of Neighborhood Environmental Survey findings and other research, we are considering whether to lower below DNL 65 dBA, the definition of the level of significant noise exposure for actions subject to environmental review. And are also considering modifying the definitions of the levels of noise exposure that are deemed normally compatible with airport operations as set forth in Part 150.

[00:15:03] Now is the time to provide input as FAA has not yet made any decisions regarding what, if any, of its noise policy will be updated. Your input will help us understand how we can improve community understanding and expectations regarding future noise exposure, and also how FAA makes decisions regarding the topic.

[00:15:23] Carolyn McCulley: In these webinars, a team of four FAA representatives fielded questions about a variety of topics and provided clarification for viewers about what the FAA could and could not change. Here, Adam Scholten, an FAA Environmental Protection Specialist, reminds listeners of the limits of the FAA's ability to change aircraft noise exposure.

[00:15:44] Adam Scholten (FAA): As described in the Federal Register Notice, the FAA's ability to control the change in aircraft noise exposure is limited in what was mentioned in the comment. What I mean by that is that the limitation really is our lack of authority on our part to control the primary factors that drive aviation noise, which are the frequency, the location, the time of operation of the aircraft, as well as the specific aircraft that are being flown on any particular route at any particular time. They're really market-driven decisions and they're not under our control, and those do represent the primary source for the experience of noise that people are experiencing on the ground.

[00:16:22] Carolyn McCulley: During the final FAA webinar, Andrew Brooks, the Regional Environmental Program Manager at the FAA's Eastern Region Airports Division, specifically mentioned Dulles Airport—and naturally, my ears perked up. 

[00:16:35] Andrew Brooks (FAA): And then we have airport authorities like MWAA at Dulles, which is doing a lot of land use compatibility planning in terms of sharing noise exposure maps, but they've had some procedure changes in the last few years.

[00:16:50] And those procedure changes, unfortunately, were timed in a way between some of their updates to their land use compatibility planning, wherein new communities had grown in certain areas, despite concerns that were raised. 

[00:17:05] Carolyn McCulley: Yeah, so I'm not unsympathetic to the challenges of compatible land use planning for airports, but Dulles Airport updated its 1993 noise exposure map in 2019.

[00:17:18] So yeah, a lot of things can change in nearly 30 years. And, unfortunately, the noise exposure map that Dulles created is not based on actual and current noise. Most U.S. airports that publish noise exposure maps are doing so as part of the FAA's Part 150 process. That's a voluntary process airports undergo to look at the current air traffic and what is expected to be the demand for air traffic for the next five years.

[00:17:46] But Dulles Airport does not use a demand forecast for creating its noise exposure maps. Instead, it creates capacity noise maps, projecting what the noise would be like if the airport hit certain levels of annual flight operations. The 2019 noise map that Dulles published in 2020 reflected the noise of what one million annual flight operations would be out of Dulles.

[00:18:12] The problem is, no airport in the world has ever reached one million annual operations, and Dulles itself has been hovering around 300,000 annual flights for years. So, the communities living near Dulles find themselves in DNL noise contours that aren't based on actual flight traffic at all—and that just adds a whole new layer of confusion.

[00:18:34] That said, I do recommend watching these Noise Policy Review webinars on YouTube. The introduction is the same in each one, but the Q&A is different in each webinar and offers more technical specifics than this podcast has the time to go into. 

[00:18:50] In response to its outreach, the FAA received more than 4,800 comments from across the country. More than 3,900 of them came from individuals. And 249 were submitted by a range of organizations, including community groups, local governments, airport sponsors, etc. The FAA is currently reviewing those comments and will update its Noise Policy Review page with new information as it becomes available.

[00:19:29] Obviously, understanding how aviation noise is measured and how it impacts people on the ground is not an easy task. Ultimately, because of this feedback, the FAA may change its primary metric, or add supplemental metrics or guidance. But certainly, local municipalities and residents alike need better tools to make decisions about land use and where to live.

[00:19:53] Minimally, if a noise exposure map uses the DNL metric, it would be more helpful for everyone if the number of flights that are represented in that DNL contour were included. Because the aggravation of repeated interruptions by a parade of jets overhead can be very significant. 

[00:20:14] The Noisy Skies team is excited to attend the Aircraft Noise and Emissions Symposium in Palm Springs, California in just a few days. At this event, we'll get to hear an update on the FAA's Noise Policy Review and meet several of the people from this episode. Of course, you can count on hearing all about it in a future podcast episode.

[00:20:39] Noisy Skies is brought to you by The Aloft Group. Aloft draws on decades of aviation experience to help communities navigate the complexity of aviation noise. To learn more about how The Aloft Group can help your community, visit This episode was written and edited by me, Carolyn McCulley.

[00:21:00] Do you have questions or comments for the show? We'd love to hear from you. Drop us a line at, and then join me next time, wherever you get your favorite podcasts. Thank you for listening.