Aircraft Noise and Air Traffic Control Modernization

Aircraft Noise and Air Traffic Control Modernization

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January 27, 2020
Aircraft Noise and Air Traffic Control Modernization
The Federal Aviation Administration (FAA) is replacing its
Philadelphia region, which has also faced considerable
radar-based air traffic control system with a satellite-based
community criticism.
navigation and tracking system called NextGen. The stated
purpose of NextGen is to increase airspace utilization and
Measuring Aircraft Noise
improve air traffic flows, allowing airliners to fly more
Put simply, noise is unwanted sound. Sound intensity is
efficiently, thereby cutting fuel consumption and reducing
measured in terms of pressure exerted on the ear using a
emissions. In order to achieve these objectives, FAA is
logarithmic decibel (dB) scale. For roughly every 10 dB
reconfiguring airspace by modifying flight routes, and by
increase, humans perceive a sound to double in loudness, so
creating new approach and departure procedures at airports.
70 dB would sound roughly twice as loud as 60 dB. A noise
Planning and implementing these changes has met with
registering 80 dB would sound roughly twice as loud as 70
backlash from some communities where overflights have
dB, and four times as loud as 60 dB.
become more frequent, prompting legislative action
regarding FAA’s approaches to measuring aircraft noise,
FAA regulations require aircraft noise measurements as
assessing impacts, and conducting community outreach.
part of the certification process for new aircraft designs.
Sound levels are measured under three conditions: (1)
NextGen Changes
during full-power takeoff measured from a position offset
As part of the NextGen effort, FAA is establishing new
450 meters (m) laterally from the runway centerline and
approach and departure patterns at airports to implement
abeam the point of peak noise; (2) flyover, measured from
precision navigation capabilities. FAA refers to these
directly beneath the flightpath at a position 6,500m from the
procedures as Performance Based Navigation (PBN). To
start of the takeoff roll and past the point of initial power
implement PBN in complex airspace around major
reduction after takeoff; and (3) approach, measured from
metropolitan areas, FAA is conducting a number of projects
directly beneath the flightpath at a point 2,000m from the
under its “metroplex” program. In planning each metroplex
runway threshold. A normalization procedure, called the
airspace reconfiguration, FAA prepares an environmental
Effective Perceived Noise Level (EPNL), is used to account
assessment allowing for input from communities that may
for tones and sound duration. The sum of these three
be affected by proposed changes to flight patterns.
measurements must be below the noise certification
Currently there are 11 metroplex projects in various stages
standard for that particular aircraft, which depends on its
of study and implementation (see Figure 1).
maximum takeoff weight and the number of engines.
Figure 1. FAA Metroplex Projects
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
Source: CRS analysis of FAA data.
cumulative reduction of 7 EPNLdB below “Stage 4”
standards. Since these standards apply only to new aircraft
FAA reversed an earlier airspace restructuring it had
designs, it usually takes several years for operational noise
implemented in Phoenix, AZ, following numerous noise
levels to noticeably decrease as airline fleets are slowly
complaints, criticism regarding limited community
replaced.
involvement in the process, and legal action challenging
implementation of the flight path changes. FAA previously
Assessing Community Response
implemented a major airspace redesign separate from its
To describe noise levels in communities, aircraft noise is
metroplex program in the New York-New Jersey-
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
more noticeable even if the aggregate noise level is
aggregated over the 24-hour period, and penalties of 10 dB
comparably lower.
are added to nighttime flights between 10 p.m. and 7 a.m.
The resulting single descriptor of the noise environment is
Figure 3. Reduction in U.S. Population Exposed to
known as the day-night average sound level (DNL).
Significant Aircraft Noise and Growth in Air Traffic
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.
Source: U.S. Department of Transportation, Volpe Center, Reducing
For this reason, FAA advises that residential land use is
Aviation Noise, Advancing the Aviation Enterprise.
generally not suitable for locations above 65 DNL.
While aircraft are considerably quieter than decades ago,
Figure 2. The Shultz Curve
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.
Legislative Response

Source: Federal Interagency Committee on Noise, Federal Agency
Initially, Congress urged FAA to quickly implement
Review of Selected Airport Noise Analysis Issues, August 1992.
NextGen changes and Performance Based Navigation
procedures. The FAA Modernization and Reform Act of
Noise Reduction Measures
2012 (P.L. 112-95) included language allowing FAA to
Efforts to reduce aircraft noise impacts focus on three key
proceed with the lowest level of environmental review,
strategies: (1) quieting noise sources such as aircraft
known as a categorical exclusion. Following backlash from
engines and airframes, (2) increasing the distance between
this approach, particularly in Phoenix, Congress
aircraft and communities through land use planning and
reexamined how FAA was conducting its noise analyses
noise abatement procedures, and (3) attenuating sound
and engaging with communities regarding its metroplex
along the transmission path through means such as
projects. The FAA Reauthorization Act of 2018 (P.L. 115-
“soundproofing” homes by installing heavier insulation and
254) mandated that FAA complete its review of alternatives
thicker, double-paned windows. The combination of these
to DNL and 65 DNL guidelines. The legislation directed
approaches has led to a significant reduction in the
FAA to study the potential health and economic impacts of
residential population exposed to aircraft noise levels above
aircraft noise on communities and to assess whether aircraft
65 DNL over the past four decades, despite considerable
approach and takeoff speed restrictions could reduce noise
growth in air traffic (see Figure 3).
impacts without affecting flight safety. It also required FAA
to allow airports to request dispersed or fanned departure
Noise Concerns
headings and flight track variations to reduce the
As FAA has implemented NextGen, noise complaints
concentration of flight paths over certain neighborhoods
regarding new flight patterns often have come from
due to PBN, improve its community engagement practices,
neighborhoods where cumulative aircraft noise levels are
and appoint regional noise ombudsmen to liaise with
well below 65 DNL. Two key factors appear to be at play.
communities impacted by noise stemming from NextGen
First, the flight patterns are new, so aircraft noise is
changes. FAA officials testified in September 2019 that the
affecting communities that rarely experienced overflights in
agency was working to meet these requirements.
the past. Second, in some, but not all, of these communities
the background or ambient noise levels are lower than in
Bart Elias, Specialist in Aviation Policy
other neighborhoods impacted by aircraft noise. In locations
IF11420
where ambient noise is lower, aircraft overflights might be
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Aircraft Noise and Air Traffic Control Modernization

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