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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.

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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 I. 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.

        ~asr~i ~Z  crrNoise
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.


To describe noise levels in communities, aircraft noise is
modeled based on flight operations across an average busy


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