Aircraft Noise and Air Traffic Control Modernization

January 27, 2020

Aircraft Noise and Air Traffic Control Modernization

The Federal Aviation Administration (FAA) is replacing its

radar-based air traffic control system with a satellite-based

navigation and tracking system called NextGen. The stated

purpose of NextGen is to increase airspace utilization and

improve air traffic flows, allowing airliners to fly more

efficiently, thereby cutting fuel consumption and reducing

emissions. In order to achieve these objectives, FAA is

reconfiguring airspace by modifying flight routes, and by

creating new approach and departure procedures at airports.

Planning and implementing these changes has met with

backlash from some communities where overflights have

become more frequent, prompting legislative action

regarding FAA’s approaches to measuring aircraft noise,

assessing impacts, and conducting community outreach.

NextGen Changes

As part of the NextGen effort, FAA is establishing new

approach and departure patterns at airports to implement

precision navigation capabilities. FAA refers to these

procedures as Performance Based Navigation (PBN). To

implement PBN in complex airspace around major

metropolitan areas, FAA is conducting a number of projects

under its “metroplex” program. In planning each metroplex

airspace reconfiguration, FAA prepares an environmental

assessment allowing for input from communities that may

be affected by proposed changes to flight patterns.

Currently there are 11 metroplex projects in various stages

of study and implementation (see Figure 1).

Figure 1. FAA Metroplex Projects

Source: CRS analysis of FAA data.

FAA reversed an earlier airspace restructuring it had

implemented in Phoenix, AZ, following numerous noise

complaints, criticism regarding limited community

involvement in the process, and legal action challenging

implementation of the flight path changes. FAA previously

implemented a major airspace redesign separate from its

metroplex program in the New York-New Jersey-

Philadelphia region, which has also faced considerable

community criticism.

Measuring Aircraft Noise

Put simply, noise is unwanted sound. Sound intensity is

measured in terms of pressure exerted on the ear using a

logarithmic decibel (dB) scale. For roughly every 10 dB

increase, humans perceive a sound to double in loudness, so

70 dB would sound roughly twice as loud as 60 dB. A noise

registering 80 dB would sound roughly twice as loud as 70

dB, and four times as loud as 60 dB.

FAA regulations require aircraft noise measurements as

part of the certification process for new aircraft designs.

Sound levels are measured under three conditions: (1)

during full-power takeoff measured from a position offset

450 meters (m) laterally from the runway centerline and

abeam the point of peak noise; (2) flyover, measured from

directly beneath the flightpath at a position 6,500m from the

start of the takeoff roll and past the point of initial power

reduction after takeoff; and (3) approach, measured from

directly beneath the flightpath at a point 2,000m from the

runway threshold. A normalization procedure, called the

Effective Perceived Noise Level (EPNL), is used to account

for tones and sound duration. The sum of these three

measurements must be below the noise certification

standard for that particular aircraft, which depends on its

maximum takeoff weight and the number of engines.

Noise certification standards, referred to as “stages,” have

become more stringent over the years as engine and

airframe noise reduction technology has improved. Aircraft

produced in the late 1960s through 1975 had to meet “Stage

2” noise standards. In the mid-1970s, FAA set more

stringent “Stage 3” criteria for new aircraft and aircraft

engines, which became mandatory for all new jet airplanes

by the late 1980s. Noisier “Stage 2” airplanes were

gradually phased out and were completely banned from

routine operation in U.S. airspace by 2016. In 2005, FAA

promulgated “Stage 4” standards, which mandated a

cumulative reduction of 10 EPNLdB across the three

measurement conditions compared to “Stage 3,” and in

2017, FAA adopted “Stage 5” standards requiring a further

cumulative reduction of 7 EPNLdB below “Stage 4”

standards. Since these standards apply only to new aircraft

designs, it usually takes several years for operational noise

levels to noticeably decrease as airline fleets are slowly

replaced.

Assessing Community Response

To describe noise levels in communities, aircraft noise is

modeled based on flight operations across an average busy

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Aircraft Noise and Air Traffic Control Modernization

day for an airport or flight route. Noise events are

aggregated over the 24-hour period, and penalties of 10 dB

are added to nighttime flights between 10 p.m. and 7 a.m.

The resulting single descriptor of the noise environment is

known as the day-night average sound level (DNL).

Since the 1970s community reaction to aircraft noise levels

has been described in terms of annoyance response

measured through community surveys. Based on analyses

of annoyance response as a function of DNL, FAA has

developed recommendations regarding acceptable land

uses. In a synthesis of social surveys examining community

response to aircraft noise, commonly referred to as the

“Shultz curve” (see Figure 2), 65 DNL corresponded to

roughly one out of every eight individuals expressing high

levels of annoyance. FAA concluded that strong community

reaction to aircraft noise levels is likely above this level.

For this reason, FAA advises that residential land use is

generally not suitable for locations above 65 DNL.

more noticeable even if the aggregate noise level is

comparably lower.

Figure 3. Reduction in U.S. Population Exposed to

Significant Aircraft Noise and Growth in Air Traffic

Source: U.S. Department of Transportation, Volpe Center, Reducing

Aviation Noise, Advancing the Aviation Enterprise.

While aircraft are considerably quieter than decades ago,

airlines now typically operate more frequent flights with

smaller aircraft that carrier fewer passengers. Strong

community reaction may be, in part, a reaction to the

number of audible overflights rather than the average noise

described by the DNL metric. An ongoing question is

whether these negative reactions will endure. This may

depend to some extent on community characteristics (such

as population demographics and ambient noise levels), as

well as FAA’s efforts to engage in meaningful community

outreach and willingness to explore viable options to

address community concerns.

Figure 2. The Shultz Curve

Legislative Response

Source: Federal Interagency Committee on Noise, Federal Agency

Review of Selected Airport Noise Analysis Issues, August 1992.

Noise Reduction Measures

Efforts to reduce aircraft noise impacts focus on three key

strategies: (1) quieting noise sources such as aircraft

engines and airframes, (2) increasing the distance between

aircraft and communities through land use planning and

noise abatement procedures, and (3) attenuating sound

along the transmission path through means such as

“soundproofing” homes by installing heavier insulation and

thicker, double-paned windows. The combination of these

approaches has led to a significant reduction in the

residential population exposed to aircraft noise levels above

65 DNL over the past four decades, despite considerable

growth in air traffic (see Figure 3).

Noise Concerns

As FAA has implemented NextGen, noise complaints

regarding new flight patterns often have come from

neighborhoods where cumulative aircraft noise levels are

well below 65 DNL. Two key factors appear to be at play.

First, the flight patterns are new, so aircraft noise is

affecting communities that rarely experienced overflights in

the past. Second, in some, but not all, of these communities

the background or ambient noise levels are lower than in

other neighborhoods impacted by aircraft noise. In locations

where ambient noise is lower, aircraft overflights might be

Initially, Congress urged FAA to quickly implement

NextGen changes and Performance Based Navigation

procedures. The FAA Modernization and Reform Act of

2012 (P.L. 112-95) included language allowing FAA to

proceed with the lowest level of environmental review,

known as a categorical exclusion. Following backlash from

this approach, particularly in Phoenix, Congress

reexamined how FAA was conducting its noise analyses

and engaging with communities regarding its metroplex

projects. The FAA Reauthorization Act of 2018 (P.L. 115254) mandated that FAA complete its review of alternatives

to DNL and 65 DNL guidelines. The legislation directed

FAA to study the potential health and economic impacts of

aircraft noise on communities and to assess whether aircraft

approach and takeoff speed restrictions could reduce noise

impacts without affecting flight safety. It also required FAA

to allow airports to request dispersed or fanned departure

headings and flight track variations to reduce the

concentration of flight paths over certain neighborhoods

due to PBN, improve its community engagement practices,

and appoint regional noise ombudsmen to liaise with

communities impacted by noise stemming from NextGen

changes. FAA officials testified in September 2019 that the

agency was working to meet these requirements.

Bart Elias, Specialist in Aviation Policy

https://crsreports.congress.gov

IF11420

Aircraft Noise and Air Traffic Control Modernization

Disclaimer

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