Growing up in a neighborhood just over a mile north of JFK Airport’s Runway 22R/L, I know a thing or two about aircraft noise. We’re talking about the mid-1970s too, when 707s, 727s, and DC-9s freely roamed the skies well before the quieter Stage 3 noise requirements were in place. Ah yes, then there was the Concorde. It felt like time stopped for a minute or so as the sleek supersonic airliner passed a mere few hundred feet above my garage on approach. The vibrations from its engines rattled dishes in my mother’s cupboard and good luck if you were at a pivotal point in any TV show. Of course, as a wide-eyed aviation buff, I relished the extra loud engine noise and would always bolt to the backyard to watch the Concorde’s iconic “droop-snoot” in action. However, I’m fairly sure my neighbors did not share my same enthusiasm for these routine aerial encounters. I can’t say that I blame them.
For Flying Out Loud!
Fast forward several decades, and my, how things have changed. I no longer live a half dozen golf swings from a major international airport, but I’m keenly aware of the tremendous strides the FAA has made in terms of reducing and mitigating aircraft noise. Still, the current situation with regard to noise is a dichotomy of sorts. On one hand, the number of people exposed to significant aviation noise in the United States has declined 90% from roughly 7 million in the 1970s, to just over 400,000 today. This also occurred as total enplanements increased by nearly a factor of five, from 200 million in 1975 to more than 850 million today.
Despite this favorable shift over time, a recent noise survey revealed a somewhat curious discovery. Data from the FAA’s Neighborhood Environmental Study (NES), which was released this past January, indicated a substantially higher percentage of people were “highly annoyed” over the entire range of aircraft noise levels, including those at lower levels (below DNL 65 dBA). So how does that happen with so many fewer people exposed to aviation noise? It’s the same question FAA experts are currently tackling in their bid to rethink the way noise is addressed, including figuring out ways to better understand how people perceive and respond to different types of noise. “This is a nuanced story,” explains Dr. James Hileman, the FAA’s Chief Scientific and Technical Advisor for Environment and Energy during a recent webinar on the NES results. “The noise experience today is very different than it was in decades past.”
Indeed it is. What may help explain this growing distaste for aircraft noise are changes in a range of factors including survey methodology, how aircraft operate, population distribution, how people live and work, and societal response to noise. The NES is the first major update the federal government has undertaken to assess annoyance from aircraft noise since a 1992 reassessment of survey data collected in the 1970s was conducted. The NES attempted to capture some of these nuances and provide more recent quantitative data, which the FAA could use going forward. But before we get into those details, a brief background on sound metrics and the agency’s noise efforts might provide helpful context.
Simply stated, noise is unwanted sound. As we mentioned, there is a great deal of subjectivity involved with that assessment, but also a physical, more objective component as well. For example, we use decibels to measure sound intensity on a logarithmic scale. (Fun fact: a decibel is actually 1/10 of a bel (B), a unit originally used to quantify telegraph signal loss and named after Alexander Graham Bell). But to account for the way people respond to sound, we use the A-weighted scale (dBA). This accounts for both intensity and how the human ear responds to sound, focusing on frequencies that would affect us most (e.g., a crying baby vs. the low rumble of thunder).
Because people are exposed to sounds that vary in length and loudness, the FAA must use metrics that take these factors into account. The FAA’s aviation noise webpage (faa.gov/go/aviationnoise) goes into great detail on these metrics, but we’ll focus on one in particular here that helps measure noise exposure in a uniform manner — the day-night average sound level (DNL).
DNL is a metric that reflects a person’s cumulative exposure to sound over a 24-hour period and is the standard metric used for all FAA noise studies. It takes into account both the noise from a particular aircraft, as well as the total number of aircraft operations over a single day (see Figure 1). For example, the DNL value for a single very loud event (like my Concorde experience) could equal that of several hundred aircraft that are less noisy, like near a busy general aviation airport. It also accounts for the complex set of variables that could cause noise to vary, like aircraft weight and configuration, weather, and time of year. To account for increased noise sensitivity at night, DNL is weighted to assess a 10 dBA “penalty” for operations between 10:00 pm and 7:00 am.
The FAA began using a DNL of 65 dBA as a threshold for significant noise exposure in response to the 1976 Aviation Noise Abatement Policy. Together with federal land-use guidelines, this helped the FAA to significantly reduce the number of people living in areas exposed to aviation noise as was pointed out earlier. The agency also established eligibility for noise mitigation funding, like sound insulation for schools or homes.
Peace of Your Mind
To get to the meat of the matter on noise, the FAA also had to find a way to represent the effect of noise exposure on people. Researchers use the term “annoyance” to capture the varied adverse reactions people have to different levels of noise exposure. With the help of social surveys, this relationship can be measured with what’s known as a dose-response curve. If that term sounds like it belongs in a medical textbook, you’re correct. It’s a term also used within the medical field to measure the relationship of an exposure and a reaction. In fact, the FDA used dose-response curves to help pinpoint optimal dosing amounts for COVID-19 vaccines. In the FAA’s case, the dose is aircraft noise and the response is a measure of how it annoys people. Current FAA noise policies, including the DNL 65 dBA threshold, are driven by a dose-response curve developed in the 1970s, known as the Schultz Curve. Although the Schultz Curve was reviewed and revalidated in 1992, its underlying survey data is 40 years old.
That brings us to the FAA’s most recent effort to better understand the impact of aircraft noise exposure, the NES. By measuring responses to a modern fleet using updated data collection and analysis tools, the FAA was able to depict a more contemporary picture of the response to aircraft noise exposure. The NES involved surveying more than 10,000 residents living near 20 representative airports. A range of airport types were selected for the study including larger commercial airports as well as medium-sized airports with a healthy mix of general aviation and rotorcraft operations like Des Moines International and Savannah/Hilton Head International.
As the right side of Figure 2 indicates, the new national curve reflects a much higher level of annoyance and a substantial change in the way people perceive aircraft noise. To help better understand and address these changes, the FAA issued a Federal Register Notice in January (86 FR 2722) to make the public aware of the NES results and to solicit feedback on where the FAA could further direct resources. The agency is now reviewing the more than 4,100 responses received during the comment period with the hope that this feedback will help shed light on the shift in increased annoyance levels and inform future steps.
“We will look at these results alongside outputs from other noise research programs to inform future actions,” said Don Scata, Noise Division Manager with the FAA’s Office of Environment and Energy. This includes ongoing research to study the impact to cardiovascular health and sleep disturbance. While these other programs may take some time to complete, the FAA is committed to keeping the public and stakeholders updated with any progress. Scata adds that the NES results are “an important element of a broader portfolio of research and community engagement to investigate and mitigate the impacts of aircraft noise.”
To view the FAA’s Federal Register Notice on Aircraft Nosie Policy and submitted comments, go to bit.ly/FAAFRN.
In the meantime, the FAA remains actively engaged with other government and industry stakeholders to explore ways to reduce noise exposure, including how certain emerging technologies could play a role. The FAA is currently working with NASA and the ASCENT (ascent.aero) Center of Excellence on studying noise from electric-powered aircraft, advanced air mobility vehicles, and the X-59 Quiet SuperSonic Technology (QueSST) aircraft, a kinder and quieter Concorde if you will. There’s also the FAA’s ongoing work with the Continuous Lower Energy, Emissions, and Noise (CLEEN) program that is helping to accelerate the development of noise-friendly aircraft and engine technologies (bit.ly/FAACLEEN). It’s worth noting that the single most influential factor in reducing aircraft noise exposure has been the transition to quieter aircraft over the years through stringent noise standards.
On a more local level, the FAA has taken a host of actions in recent years to meaningfully engage communities with regard to noise. This includes hiring community engagement officers in each region and working with airport authorities to address community noise concerns. The FAA also created the Fly Neighborly noise abatement training program (bit.ly/FlyNeighborly) that teaches helicopter pilots about noise abatement procedures and noise-minimizing flight techniques.
Additionally, the agency continuously reviews air traffic procedures across the country to find ways to reduce aircraft noise while maintaining safety. For example, we’re already seeing noise (and fuel) benefits from the use of idle thrust approaches and narrower flight paths with performance-based navigation procedures for both commercial and general aviation operations.
Let’s Go Someplace More Quiet
With these ongoing efforts, coupled with a new comprehensive noise survey, the FAA is demonstrating its longstanding commitment to the environment and remains well poised to gain a keener understanding of the impact of aircraft noise exposure on the public. We encourage you to stay tuned as the FAA turns a new page on its efforts to adopt quieter, cleaner, and more efficient air transportation.
Not sure who to contact with an aviation noise concern? Want to learn more about ways the FAA engages with communities? Visit faa.gov/noise.
✨ Sound Judgement for Using Drones
By Diana Robinson, FAA’s UAS Integration Office
Bzzzzzzzzz. You might think you hear a bothered bunch of busy bees if you are in hearing range of a drone’s departure from terra firma. Nearly all small unmanned aircraft systems (sUAS) fall below the decibel level that can be harmful to human hearing; however, drone sounds can be a nuisance. They can also hinder an operation’s objective: noise makes surveillance obvious and isn’t a welcome wedding party guest even when participants really want drone photography.
Using drones for wildlife observation is another example. As scientists and naturalists are quick to note, animals are not particularly fond of bees or other stinging insects. A drone that quickly approaches a herd can cause a stampede. Drones have also been known to draw the attention of birds of prey, creating dangers to both bird and drone. Gustavo Lozada, a technology manager for the Nature Conservatory in Colorado, acknowledges that drones are an important tool in wildlife research and protection. Drones can track elephants in Africa, and they have helped eliminate activities like poaching, illegal fishing, and wildlife trafficking. Scientists can observe vulnerable species by tracking migration routes and patterns.
Recognizing the nuisance of drone noise, though, drone researchers are working with manufacturers to help reduce the buzzing noise they create. In the meantime, you need to use sound judgement (pun intended) when planning your mission, keeping risks and rewards of your decisions in mind while flying your drone.
Whether using drones near animals or humans, common sense is always in order. Lozada has formulated a method for slowly introducing the drone near animals by keeping a safe distance until they get used to the noise. The aim is to not scare the animals or disrupt their natural behaviors. The World Wildlife Fund and University of Exeter recommends drone pilots adopt a precautionary principle, since little is known about animals’ sensitivity to drones. Their recent report, “Drones for Conservation,” shares best practices for operating around endangered species and sensitive habitats. They encourage you to think about your launch and recovery sites and to select a location that is away from animals.
When flying your drone near people, always aim to be courteous, respectful, and responsible. Let others know in advance about your drone operation. Be mindful of their privacy. Letting people know what to expect eliminates the startle factor, and that could help unleash curiosity and even inspire interest in flying drones.
We know to follow FAA rules when flying our unmanned aircraft, but it’s also important to plan carefully. Check local, state, and national laws. Select the correct drone for the job. Pay attention to who and what are below the planned operation. In short, small steps go a long way toward assuring mission success.
To learn more about drones helping with conservation efforts, go to bit.ly/2Q9MLRr.
Diana Robinson is a project specialist in the Operational Programs Branch of the FAA’s UAS Integration Office.
Tom Hoffmann is the managing editor of FAA Safety Briefing. He is a commercial pilot and holds an A&P certificate.