January 26, 2022
Aviation Concerns Regarding the Rollout of 5G Wireless
Telecommunications Networks
The rollout of fifth-generation (5G) wireless
aircraft terrain alerting systems that provide pilots with
telecommunications networks in the United States has
information and warnings about terrain and obstacle
roiled passenger and cargo airlines and other aviation
clearance. Radar altimeters also provide data to automated
operators over fears that certain mid-band or C-band 5G
flight control systems used for vertical flight guidance at
signals could interfere with aircraft radio altimeters. These
low altitude, especially during approach to landing. While
concerns prompted the Federal Aviation Administration
airplanes can rely on other systems, including precision
(FAA) to issue alerts to aircraft operators in late 2021 about
instrument landing systems, to descend to about 200 feet
possible flight safety risks. FAA asked aircraft operators for
above the ground, radar altimeters are essential to providing
related data, urged them to educate pilots about potential
vertical guidance below 200 feet in low-visibility
disruptions, and prohibited certain flight procedures as a
conditions when pilots are unable to clearly see the runway.
safety precaution. At the urging of FAA, the Department of
While such capabilities are essential for all-weather
Transportation, the White House, and some Members of
commercial flight operations, radar altimeters are not
Congress, telecommunications companies agreed to
commonly found on small general aviation aircraft.
voluntarily delay the rollout of 5G service near airports,
originally scheduled for early December 2021, until July
FAA, along with aviation regulators from other countries,
2022, to avoid air travel disruptions. This will give FAA
first raised concerns about wireless deployments in the C-
and avionics equipment manufacturers additional time to
band in 2015. They cautioned that 5G signals transmitted
more thoroughly assess whether C-band 5G signals might
on nearby frequencies could potentially interfere with radio
interfere with flight operations and whether equipment
altimeters, particularly if high-powered 5G base stations are
upgrades or other mitigation actions will be needed to
placed close to airport runways. Although not required by
adequately shield aircraft systems from 5G interference.
regulation, most radio altimeters currently in use have mask
filters to block signals on nearby frequencies that could be
Radiofrequency Spectrum and 5G Signals
mistaken for reflected radio altimeter signals. However, it is
5G networks are being installed all around the world, but
uncertain whether these filters will adequately block more
are being assigned different frequency bands in different
powerful 5G signals in all cases, as radio altimeter signals.
countries. While low-band (below 1 gigahertz (GHz)) and
high-band (above 24 GHz) 5G frequencies pose no
A study by RTCA, an aviation industry technical advisory
particular concern to aviation, the assignment of C-band
group founded as the Radio Technical Commission for
frequencies in the range of roughly 3 to 5 GHz has alarmed
Aeronautics, concluded that expected interference levels
the aviation industry over potential interference with radio
from fundamental 5G emissions in the 3.7-3.98 GHz range
altimeters. Europe has allocated spectrum between 3.4 and
and spurious or stray 5G emissions that bleed over into the
3.8 GHz for C-band 5G, while in Japan, frequencies from
4.2-4.4 GHz band were likely to exceed safe interference
3.4 to 4.1 GHz are assigned. In the United States, the
limits for all envisioned 5G transmitter configurations
Federal Communications Commission (FCC) approved use
across all categories of airplanes and helicopters equipped
of spectrum between 3.7 and 3.98 GHz for 5G in 2020, and
with radio altimeters. Moreover, it determined that stray 5G
subsequently auctioned licenses in this band to
emissions that might bleed over into the band reserved for
telecommunications providers. U.S. providers paid over
radio altimeters would not be considered compliant with
$81 billion for C-band licenses, and are eager to launch
international recommendations for radiofrequency
service in order to recoup these costs and realize a return on
protection criteria.
investment in 5G technology that will give wireless
customers faster data transmission speeds and greater
The FCC countered that the RTCA findings assume a
reliability than fourth-generation (4G) wireless service.
worse-case scenario, and that alternative testing found that
FCC-mandated protections, including limits on the strength
Potential Interference with Radio Altimeters
of 5G signals and 220 MHz of spectral separation between
Worldwide, aviation operators have long used a slice of
5G signals and radio altimeters, would mitigate the
radiofrequency spectrum between 4.2 GHz and 4.4 GHz
potential for interference. Further, the FCC argued that
that is exclusively reserved for radio altimeters. These
properly engineered radio equipment should not be prone to
devices, frequently installed on airliners, regional and
harmful interference from 5G signals.
business jets, turboprops, advanced helicopters, and
military aircraft measure aircraft altitude above the ground
Near-Term Mitigation Actions
by timing how long it takes for a directional radio
Telecommunications providers voluntarily pushed back 5G
transmission to reach the terrain below and bounce back to
launch schedules from early December 2021 to January
an onboard receiver. Radar altimeters provide input to
2022 to provide FAA with additional time to address radio
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Aviation Concerns Regarding the Rollout of 5G Wireless Telecommunications Networks
altimeter interference concerns. As C-band 5G deployments
been reluctant to agree to such measures, as they could
were slated to launch in early January 2022, FAA initially
reduce the availability and quality of 5G service in areas
restricted the use of approach procedures and automated
around airports. Moreover, reducing the power of these 5G
landing system operations at 88 airports where it
transmissions could give competitors that do not rely on
determined that the presence of C-band 5G signals could
these frequency bands a competitive advantage.
pose a risk of radio altimeter interference. However, service
providers subsequently agreed to voluntarily delay
Potential Long-Range Resolution
activation of 5G transmitters located close to airports until
It will ultimately be up to FAA to decide whether existing
July 5, 2022, thus creating temporary “buffer zones” around
radio altimeter systems adequately protect against 5G
airports during the first six months of the 5G rollout. If,
interference or if new replacement units that meet future
after this time, FAA decides to restrict certain flight
operational performance standards will be required. As of
procedures due to lingering 5G concerns, aircraft operators
late January 2022, FAA has provisionally approved roughly
could be forced to execute costly flight diversions in poor
90% of the U.S. commercial airline fleet equipped with
weather or cancel flights of aircraft using radio altimeters
radio altimeters to conduct low-visibility landings at
not approved by FAA for low-visibility approaches in the
airports with nearby 5G towers.
presence of 5G. Despite agreements to create temporary 5G
buffer zones around U.S. airports, some airlines, including
FAA is working with industry groups led by RTCA and its
some international airlines, canceled flights and modified
Europe counterpart, the European Organization for Civil
service in January 2022, apparently in response to
Aviation Equipment or EUROCAE, to develop minimum
continued uncertainty regarding possible disruptions to low-
operational performance standards for future radio
visibility operations over 5G interference concerns.
altimeters that will not be susceptible to potentially harmful
radiofrequency interference. Once these standards are
Approaches in Other Countries
established and adopted by FAA, manufacturers can begin
Other countries, including Canada, have initially restricted
to design, build, and supply units that are not prone to
the installation of 5G transmitters near airports. The 5G
potential impacts from C-band 5G. Replacement of radio
rollout in Europe over the past three years has not generated
altimeters, however, might prove costly to aircraft
the same concerns from aviation, in part because the
operators, including the military. The airline industry and
approved frequencies have greater separation from radio
other civilian operators might ask for federal relief if faced
altimeter bands than in the United States, reducing the
with significant costs to upgrade radio altimeters.
likelihood of interference. Moreover, some European
countries, notably France, have insisted that
The potential impacts of 5G are not limited to operations
telecommunications providers implement additional
around airports. Helicopters responding to medical
mitigation measures to reduce potential conflicts between
emergencies also rely on radio altimeters when landing to
5G signals and radio altimeters, including restricting power
pick up patients. Citing the critical societal importance of
output of 5G towers, restricting placement of 5G antennas
helicopter emergency medical operations, FAA has granted
in buffer zones near airports, and requiring that 5G antennas
temporary regulatory relief from radio altimeter
near airports be tilted downward to reduce the likelihood of
requirements for medical helicopters conducting night
interference with flight operations (see Figure 1).
vision goggle operations, so long as ground observers
remain in radio contact with pilots to guide them regarding
Figure 1. Comparing 5G Source Mitigation in France
terrain and obstacle clearance around landing zones. This
and the United States
exemption expires in 2024, at which point medical
helicopters may also need upgraded radio altimeters.
Lingering Policy Implications
The ongoing concerns over potential aviation safety
impacts from the 5G rollout in the United States point to
broader concerns that may be of particular interest to
Congress. These include coordination between FAA and the
National Telecommunications and Information
Administration, the federal agency that represents federal
agency spectrum concerns to the FCC; FAA’s relationship
with other regulatory agencies such as the FCC; and FAA’s
ability to address complex challenges brought about by the
proliferation of wireless technologies and the rapidly
Source: Federal Aviation Administration.
evolving technical landscape in which aviation must
operate.
In Japan, where frequencies up to 4.1 GHz allocated for 5G
are even closer to radio altimeter frequencies than in the
Bart Elias, Specialist in Aviation Policy
United States, the government has restricted the placement
of 5G transmitters within 200 meters of airport approach
IF12028
paths. In the United States, however, 5G providers have
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Aviation Concerns Regarding the Rollout of 5G Wireless Telecommunications Networks
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https://crsreports.congress.gov | IF12028 · VERSION 1 · NEW