Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
AIR-21-18 R2
October 18, 2022
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin informs aircraft
manufacturers, radio altimeter manufacturers, operators, and pilots of
the planned deployment of wireless broadband networks in the 3700-3980
MHz bands (C-Band).1 C-Band wireless broadband deployment is permitted
to occur in phases with the opportunity for operations in the lower 100
megahertz of the band (3.7 -3.8 GHz) in 46 markets beginning as soon as
December 5, 2021; however, the FAA does not expect actual deployment to
commence until January 5, 2022. This SAIB recommends that radio
altimeter manufacturers, aircraft manufacturers, and operators
voluntarily provide to federal authorities specific information related
to altimeter design and functionality, specifics on deployment and
usage of radio altimeters in aircraft, and that they test and assess
their equipment in conjunction with federal authorities. Results from
that testing and assessment should be reported to the appropriate civil
aviation authorities (CAAs) and spectrum regulators. The FAA is
currently collaborating with the Federal Communications Commission
(FCC) and the National Telecommunications and Information
Administration (NTIA) to assess the need for mitigation beyond the
recommended action in this SAIB.
Background
For the past 15 years, the 3 GHz band globally has been the subject of
harmonization activity for mobile broadband, both at the International
Telecommunication Union and within regional groups. A number of
countries already have allocated and assigned spectrum for wireless
deployments in the 3 GHz range and additional countries are following
suit. Many countries around the world are already deploying wireless
networks in the bands from 3300-4200 MHz; some countries have
implemented temporary technical, regulatory and operational
mitigations, including temporary proximity and power restrictions, on
wireless broadband networks operating in bands ranging from 3700 -4200
MHz. There have not yet been proven reports of harmful interference due
to wireless broadband operations internationally, although this issue
is continuing to be studied. In the United States, there has been
wireless broadband deployment in the 3.65-3.7 GHz band since 2007. The
FCC started a proceeding to authorize mobile broadband service in the
3.55-3.7 GHz band in December 2012 and adopted final rules in April
2015 and October 2018. Commercial deployment started in September 2019,
with no known issues for altimeters to date.
With respect to 3.7-4.2 GHz, the FCC first sought comment on
introducing mobile broadband into the band in 2017. In March 2018, the
MOBILE NOW Act directed the FCC to evaluate the feasibility of
commercial wireless deployments in the 3.7 -4.2 GHz range. The FCC
started a proceeding in May 2018 and adopted the C-band Report and
Order authorizing flexible use of the 3.7 -3.98 GHz band in March 2020.
In February 2021, the FCC completed an auction of the 3.7–3.98 GHz
frequency band and subsequently issued licenses to several wireless
network providers subject to license conditions about deployment timing
and parameters. Under the FCC’s rules, actual wireless broadband
deployment will occur in phases with operations beginning only in the
lower 100 megahertz of the band (3700-3800 MHz) and only in 46 markets
as soon as December 5, 2021. (See 47 CFR §27.1412(b)(1), which
specifies the 46 market areas as Partial Economic Areas (PEAs) 1-4,
6-10, 12-19, 21-41, and 43-50. A list of PEAs is available at
https://www.fcc.gov/oet/maps/areas).
Radio altimeters operate between 4200-4400 MHz. Currently, the FAA’s
approval process for radar altimeters is based on FAA Technical
Standard Order TSO -C87A, Airborne Low-Range Radio Altimeter. TSO-C87A
does not provide criteria for compatibility with adjacent band
operations, including potential impacts associated with wireless
communications system deployments. RTCA formed a task force to assess
the interference impact of wireless broadband operations in the 3700 -
3980 MHz band on radio altimeters. Based on the work of the task force,
RTCA published a report entitled, "Assessment of C-Band Mobile
Telecommunications Interference Impact on Low Range Radar Altimeter
Operations" (RTCA Paper No. 274-20/PMC-2073). Additional information
about RTCA can be found at https://www.rtca.org/about/. The RTCA report
is under review. The FAA is actively participating in the RTCA/SC-239
committee, which is developing adjacent band compatible minimum
operational performance standards (MOPS) for future radio altimeter
designs. The FAA encourages radio altimeter manufacturers to
participate in the international radio altimeter standards development
activity conducted jointly by RTCA and EUROCAE to establish a common
set of performance requirements and compliance demonstration methods to
promote compatibility with the international adjacent-band spectrum
environment.
The FAA is currently conducting a risk assessment to ascertain whether
further mitigation is warranted in addition to the recommended actions
in this SAIB. The FAA is basing its risk assessment on the conditions
in the FCC Report and Order (R&O) in the Matter of Expanding
Flexible Use of the 3700-4200 MHz Band (FCC 20-22) and 3GPP
specification TS 38.104 V17.2.0 (2021-06). Further, in the event that
wireless broadband deployment conditions evolve, if the FAA becomes
aware of further relevant information or guidance, or if additional
information further validates or invalidates concerns of potential
harmful interference, the FAA will update its risk assessment.
Therefore, in preparation for the December 2021 wireless network
deployment in the 3700 -3800 MHz band, the FAA recommends the following
actions and requests that affected parties voluntarily submit
information for consideration by the FAA, FCC and NTIA prior to the
planned wireless network deployments:
Radio Altimeter Manufacturers
We request that radio
altimeter manufacturers submit receiver radiofrequency (RF)
selectivity, interference tolerance masks, and baseline operational
specifications for each model number in production or still in
use, and approximate numbers of each radio altimeter model currently in
service in the United States; and, if appropriate, mark submissions as
proprietary. This information can be submitted to the FAA at
OperationalSafety@faa.gov and should indicate "Radio Altimeter SAIB" in
the subject line. The FAA will provide any information you submit to
the FCC and NTIA subject to those agencies’ processes for protection of
confidential information, where such protection is requested.
We recommend radio altimeter
manufacturers complete analysis or testing of each model number either
in production, supported, or still being employed, to determine the
susceptibility to interference from fundamental emissions in 3700-3800
MHz which is available for wireless broadband in December of 2021 and
the full 3700-3980 MHz band which will become available later, as well
as potential spurious emissions in the 4200-4400 MHz band, and assess
this susceptibility for compatibility with the adjacent spectrum
environment in accordance with the FCC R&O and 3GPP specification,
as well as the environment in other countries in which each radio
altimeter could be operated. We encourage radio altimeter manufacturers
to work with the FAA to facilitate this process.
Report instances of
erroneous altimeter performance to the FAA and FCC, or other
appropriate civil aviation authorities (CAAs) and spectrum regulators.
If the equipment is susceptible to harmful interference, determine what
design changes are necessary to remediate.
Collaborate with aircraft
manufacturers on design changes and issue guidance to operators on
potential retrofit plans for radio altimeters susceptible to harmful
interference, if necessary.
Determine any necessary
operational restrictions or actions needed to address in-flight radio
altimeter anomalies in order to maintain safe operations with radio
altimeter equipment susceptible to harmful interference and communicate
this information to CAAs, operators, and pilots.
Collect radio altimeter
retrofit plans, timelines, and completion information from operators
and share this information with MITRE Corporation. MITRE will collect,
aggregate, and de-identify proprietary information.
Aircraft Manufacturers
We request that aircraft
manufacturers submit approximate numbers of each radio altimeter model
installed on each aircraft currently in service in the United States;
and, if appropriate, mark submissions as proprietary. This information
can be submitted to the FAA at OperationalSafety@faa.gov and should
indicate "Radio Altimeter SAIB" in the subject line. The FAA will
provide any information you submit to the FCC and NTIA subject to those
agencies’ processes for protection of confidential information, where
such protection is requested.
Communicate with radio
altimeter suppliers and the FAA to ascertain equipment susceptibility
to harmful interference caused by fundamental emissions in the
3700-3800 MHz and 3700-3980 MHz band, as well as spurious emissions in
the 4200-4400 MHz band. We encourage aircraft manufacturers to work
with the FAA to facilitate this process.
Conduct testing and analysis
of the effects of loss of function, and erroneous or misleading radio
altimeter data from potential harmful interference caused by
fundamental emissions in the 3700-3800 MHz and 3700-3980 MHz band, as
well as spurious emissions in the 4200-4400 MHz band, due to wireless
broadband deployment. We encourage aircraft manufacturers to work with
the FAA to facilitate this process.
Evaluate the potential for
harmful interference on the different types of aircraft in the
manufacturer’s fleet based on aircraft architecture and radio altimeter
integration, including cascading effects.
Determine any operational
restrictions necessary or actions to take to maintain safe operations
with radio altimeter equipment susceptible to harmful interference due
to wireless broadband operation in the 3700-3800 MHz band. Restrictions
and other actions should address all systems that use the radio
altimeter. Information regarding such restrictions or other actions
should be communicated to operators, pilots, and each CAA for the
country in which the aircraft operates. Revise aircraft flight manual
procedures, if appropriate.
Update operators’ anomaly
reporting process to ensure accurate recording and reporting of
erroneous radio altimeter readings to the aircraft manufacturer.
Collaborate with radio
altimeter manufacturers and issue guidance to operators on retrofit
plans for radio altimeters susceptible to harmful interference due to
wireless broadband operation in the 3700 - 3800 MHz band. Collect radio
altimeter retrofit plans, timelines, and completion information from
operators and share this information with MITRE Corporation. MITRE will
collect, aggregate, and de-identify proprietary information.
Operators and Pilots
Review the 14 CFR Part 5
requirements for Part 121 certificate holders, if appropriate. Other
certificate holders should use the Safety Management Systems (SMS)
tools to assess the risk to each type of radio altimeter configuration
and how it impacts typical flight operations.
Remind passengers that all
portable electronic devices allowed for transport in checked baggage
(including smartphones and other devices) should be turned off and
protected from accidental activation and that compliance is mandatory
for lithium battery-powered portable electronic devices. See 49 CFR
175.10(a)(18).
Remind passengers to set all
portable electronic devices in the cabin and any carried on the
aircraft to a non-transmitting mode or turn them off. See 14 CFR 91.21,
121.306, 125.204 and 135.144.
Seek information from the
manufacturers of the aircraft and the radio altimeter on possible
effects of harmful interference due to wireless broadband deployment in
the 3700-3800 MHz band and possible pilot interventions. Provide radio
altimeter retrofit plans, timelines, and completion information to your
original equipment manufacturer. Alternatively, retrofit information
may be provided directly to the FAA at 9-AWA-AFS400-RADALT@faa.gov.
Operators should ensure
their pilots are aware of the potential degradation of the radio
altimeter capabilities and any means to compensate for in-flight radio
altimeter anomalies. Consider both erroneous altimeter readings and
loss of altimeter function.
Operators should ensure
their pilots are aware of the potential degradation to the capabilities
of safety systems and other equipment dependent upon radio altimeters
and any means to compensate for resulting anomalies. Consider both the
loss of function of the safety systems and other dependent systems and
the manners in which they may malfunction.
Operators should consider
the potential loss of pilot trust in dependent aircraft safety systems
in the assessment of existing and the development of new crew
procedures.
Operators and pilots who
experience radio altimeter anomalies should notify air traffic control,
as soon as practical. Post flight, pilots are encouraged to submit
detailed reports of radio altimeter disruptions or interference events,
as soon as practical, using the Radio Altimeter Anomaly Reporting Form
available on the FAA website at
https://www.faa.gov/air_traffic/nas/RADALT_reports/.
Paperwork Reduction Act Burden Statement
A federal agency may not conduct or sponsor, and a person is not
required to respond to, nor shall a person be subject to a penalty for
failure to comply with a collection of information subject to the
requirements of the Paperwork Reduction Act unless that collection of
information displays a currently valid OMB Control Number. The OMB
Control Number for this information collection is 2120-0731. Public
reporting for this collection of information is estimated to be
approximately 1 hour per response, including the time for reviewing
instructions, searching existing data sources, gathering and
maintaining the data needed, completing and reviewing the collection of
information. All responses to this collection of information are
voluntary; the nature and extent of confidentiality to be provided, if
any. Send comments regarding this burden estimate or any other aspect
of this collection of information, including suggestions for reducing
this burden to: Information Collection Clearance Officer, Federal
Aviation Administration, 10101 Hillwood Parkway, Fort Worth, TX
76177-1524.
For Further Information Contact
Jeffrey Palmer, Aerospace Engineer, Systems and Equipment Section, 3960
Paramount Boulevard, Lakewood, CA 90712-4137, e-mail:
OperationalSafety@faa.gov.
1 This revision clarifies the collection of radio altimeter retrofit information.