[Federal Register Volume 86, Number 234 (Thursday, December 9, 2021)]

[Rules and Regulations]

[Pages 69984-69987]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-26777]

––––––––––––––––––––––––––––––––––

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0953; Project Identifier AD-2021-01169-T; Amendment 39-21810; AD

2021-23-12]

RIN 2120-AA64

Airworthiness Directives; Transport and Commuter Category Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule; request for comments.

––––––––––––––––––––––––––––––––––

SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all transport and
commuter category airplanes equipped with a radio (also known as radar) altimeter. This AD was
prompted by a determination that radio altimeters cannot be relied upon to perform their intended
function if they experience interference from wireless broadband operations in the 3.7-3.98 GHz
frequency band (5G C-Band). This AD requires revising the limitations section of the existing
airplane/aircraft flight manual (AFM) to incorporate limitations prohibiting certain operations
requiring radio altimeter data when in the presence of 5G C-Band interference as identified by
Notices to Air Missions (NOTAMs). The FAA is issuing this AD to address the unsafe condition on
these products.

DATES: This AD is effective December 9, 2021.

The FAA must receive comments on this AD by January 24, 2022.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by
any of the following methods:
 Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the instructions for
submitting comments.
 Fax: 202-493-2251.
 Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground
Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
 Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through
Friday, except Federal holidays.

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Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by searching for and locating
Docket No. FAA-2021-0953; or in person at Docket Operations between 9 a.m. and 5 p.m., Monday
through Friday, except Federal holidays. The AD docket contains this final rule, any comments
received, and other information. The street address for the Docket Operations is listed above.

FOR FURTHER INFORMATION CONTACT: Brett Portwood, Continued Operational Safety

Technical Advisor, COS Program Management Section, Operational Safety Branch, FAA, 3960
Paramount Boulevard, Lakewood, CA 90712-4137; phone: 817-222-5390; email:
operationalsafety@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

In March 2020, the United States Federal Communications Commission (FCC) adopted final
rules authorizing flexible use of the 3.7-3.98 GHz band for next generation services, including 5G
and other advanced spectrum-based services.1 Pursuant to these rules, 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 AD
refers to “5G C-Band” interference, but wireless broadband technologies, other than 5G, may use the
same frequency band.2 These other uses of the same frequency band are within the scope of this AD
since they would introduce the same risk of radio altimeter interference as 5G C-Band.
In April 2020, RTCA formed a 5G Task Force, including members from RTCA, the FAA,
aircraft and radio altimeter manufacturers, European Organisation for Civil Aviation Equipment
(EUROCAE), industry organizations, and operators, to perform “a quantitative evaluation of radar
altimeter performance regarding RF interference from expected 5G emissions in the 3.7-3.98 GHz
band, as well as a detailed assessment of the risk of such interference occurring and impacting
aviation safety.” 3 Based on the work of the task force, RTCA published a report which concludes
that there is “a major risk that 5G telecommunications systems in the 3.7-3.98 GHz band will cause
harmful interference to radar altimeters on all types of civil aircraft–
including commercial transport airplanes; business, regional, and general aviation airplanes; and both
transport and general aviation helicopters.” 4
The report further concludes that the likelihood and severity of radio frequency interference
increases for operations at lower altitudes. That interference could cause the radio altimeter to either
become inoperable or present misleading information, and/or also affect associated systems on civil
aircraft. The RTCA report refers to FCC Report and Order (R&O) FCC 20-22,5 which identifies radio

1
The FCC's rules did not make C-Band wireless broadband available in Alaska, Hawaii, and the U.S.
Territories.
2
The regulatory text of the AD uses the term “5G C-Band” which, for purposes of this AD, has the same
meaning as “5G”, “C-Band” and “3.7-3.98 GHz”
3
RTCA Paper No. 274-20/PMC-2073, Assessment of C-Band Mobile Telecommunications Interference
Impact on Low Range Radar Altimeter Options, dated October 7, 2020 (RTCA Paper No. 274-20/PMC-2073),
page i. This document is available in Docket No. FAA-2021-0953, and at https://www.rtca.org/wp-
content/uploads/2020/10/SC-239-5G-Interference-Assessment-Report_274-20-PMC-
2073_accepted_changes.pdf.
4 RTCA Paper No. 274-20/PMC-2073, page i.
5
FCC Report and Order (R&O) FCC 20-22 in the Matter of Expanding Flexible Use of the 3.7-4.2 GHz Band,
adopted February 28, 2020, and released March 3, 2020. This document is available in Docket No. FAA-2021-
0953, and at https://www.fcc.gov/document/fcc-expands-flexible-use-c-band-5g-0.
2
frequencies and power level conditions for the new C-Band services. The RTCA report identified the
possibility of interference from both wireless emitters (on base stations, for example) as well as
onboard user handsets. The RTCA report and conclusions remain under review, including by federal
spectrum regulators. The FAA risk assessment included consideration of the RTCA report, public
comments to the RTCA report, and analyses from radio altimeter manufacturers and aircraft
manufacturers in support of the safety risk determination. The analyses FAA considered were
consistent with RTCA's conclusions pertaining to radio altimeter interference from C-Band
emissions. The FAA determined that, at this time, no information has been presented that shows radio
altimeters are not susceptible to interference caused by C-Band emissions permitted in the United
States.
Additionally, the deployment of C-Band wireless broadband networks is occurring globally. In
certain countries, deployment has already occurred in C-Band frequencies. In some countries,
temporary technical, regulatory, and operational mitigations on C-Band systems have been
implemented while aviation authorities complete their safety assessments. Under the FCC rules
adopted in 2020, base stations in rural areas of the United States are permitted to emit at higher levels
in comparison to other countries which may affect radio altimeter equipment accuracy and reliability.
The radio altimeter is an important aircraft instrument, and its intended function is to provide
direct height-above-terrain/water information to a variety of aircraft systems. Commercial aviation
radio altimeters operate in the 4.2-4.4 GHz band, which is separated by 220 megahertz from the C-
Band telecommunication systems in the 3.7-3.98 GHz band. The radio altimeter is more precise than
a barometric altimeter and for that reason is used where aircraft height over the ground needs to be
precisely measured, such as autoland or other low altitude operations. The receiver on the radio
altimeter is typically highly accurate, however it may deliver erroneous results in the presence of out-
of-band radiofrequency emissions from other frequency bands. The radio altimeter must detect faint
signals reflected off the ground to measure altitude, in a manner similar to radar. Out-of-band signals
could significantly degrade radio altimeter functions during critical phases of flight, if the altimeter is
unable to sufficiently reject those signals.
Many operators need to be able to land in low visibility conditions. These operators employ
specially certified equipment and flightcrew training in order to be able to fly closer to the ground
during approach in instrument conditions, in some cases all the way through the landing phase,
without visual reference to the runway environment. These operations can only be conducted with
reference to actual height above the ground, as measured by a radio altimeter.
Additionally, automatic and/or manual flight guidance systems on airplanes facilitate low
visibility operations and rely on accurate radio altimeter inputs. These inputs determine when and
where the aircraft flares for landing, when power reductions are made for landing, and when
automated crosswind controls and other control inputs are made. Anomalous (missing or erroneous)
radio altimeter inputs to these systems may cause the aircraft to be maneuvered in an unexpected or
hazardous manner during the final stages of approach and landing, and may not be detectable by the
pilot in time to maintain continued safe flight and landing. Inaccurate radio altimeter data can result
in pilots not trusting their instruments, eroding the foundation on which all instrument flight training
is built.
Although the FAA has determined the operations immediately at risk are those requiring a radio
altimeter to land in low visibility conditions, a wide range of other automated safety systems rely on
radio altimeter data. Harmful interference to the radio altimeter could cause these systems to operate
in an unexpected way. The FAA continues to work with inter-agency and industry stakeholders to
collect data on potential effects to these systems to determine whether additional mitigations are
necessary. The FAA determined, however, that mandatory action is not immediately required for
these systems.
The FAA plans to use data provided by telecommunications providers to determine which
airports within the United States have or will have C-Band base stations or other devices that could
potentially impact airplane systems. NOTAMs will be issued, as necessary, to state the specific
airports where the data from a radio altimeter may be unreliable due to the presence of 5G C-Band

3
wireless broadband signals.6 For this reason, this AD requires flight manual limitations that prohibit
certain operations requiring radio altimeter data at locations that will be identified by NOTAMs. Due
to the dynamic nature of both the base station activation and the ongoing process of identifying the
resulting affected airspace, including potential consideration for variability in C-Band deployment
conditions such as radiated power levels and locations, the FAA has determined that NOTAMs are
the best means to communicate changes in restrictions at affected airports.
Finally, the FAA notes that in accordance with paragraph (h) of this AD, any person may
propose and request FAA approval of an alternative method of compliance (AMOC). The proposed
AMOC must include specific conditions that would address the unsafe condition (e.g., by providing
information substantiating that certain aircraft or altimeter models are not susceptible to C-Band
radiofrequency interference).

FAA's Determination

The FAA is issuing this AD because the agency has determined the unsafe condition as
described previously is likely to exist or develop in transport and commuter category airplanes with a
radio altimeter as part of their type design.

AD Requirements

This AD requires revising the limitations section of the existing AFM to incorporate limitations
prohibiting certain operations requiring radio altimeter data when in the presence of 5G C-Band
wireless broadband signals as identified by NOTAM. These limitations could prevent dispatch of
flights to certain locations with low visibility, and could also result in flight diversions.

Compliance With AFM Revisions

Section 91.9 prohibits any person from operating a civil aircraft without complying with the
operating limitations specified in the AFM. FAA regulations also require operators to furnish pilots
with any changes to the AFM (14 CFR 121.137) and pilots in command to be familiar with the AFM
(14 CFR 91.505).

Interim Action

The FAA considers this AD to be an interim action. If final action is later identified, the FAA
might consider further rulemaking.

Justification for Immediate Adoption and Determination of the Effective Date

Section 553(b)(3)(B) of the Administrative Procedure Act (APA) (5 U.S.C. 551 et seq.)
authorizes agencies to dispense with notice and comment procedures for rules when the agency, for
“good cause,” finds that those procedures are “impracticable, unnecessary, or contrary to the public
interest.” Under this section, an agency, upon finding good cause, may issue a final rule without
providing notice and seeking comment prior to issuance. Further, section 553(d) of the APA
authorizes agencies to make rules effective in less than thirty days, upon a finding of good cause.
An unsafe condition exists that requires the immediate adoption of this AD without providing an
opportunity for public comments prior to adoption. The FAA has found that the risk to the flying
public justifies forgoing notice and comment prior to adoption of this rule because radio altimeter
anomalies that are undetected by the aircraft automation or pilot, particularly close to the ground

6
The FAA's process for issuing NOTAMs is described in FAA Order 7930.2S, Notices to Air Missions
(NOTAM), December 2, 2021.
4
(e.g., landing flare), could lead to loss of continued safe flight and landing. The urgency is based on
C-Band wireless broadband deployment, which is expected to occur in phases with operations
beginning as soon as January 5, 2022. Accordingly, notice and opportunity for prior public comment
are impracticable and contrary to the public interest pursuant to 5 U.S.C. 553(b)(3)(B).
In addition, the FAA finds that good cause exists pursuant to 5 U.S.C. 553(d) for making this
amendment effective in less than 30 days, for the same reasons the FAA found good cause to forgo
notice and comment.

Comments Invited

The FAA invites you to send any written data, views, or arguments about this final rule. Send
your comments to an address listed under ADDRESSES. Include “Docket No. FAA-2021-0953 and
Project Identifier AD-2021-01169-T” at the beginning of your comments. The most helpful
comments reference a specific portion of the final rule, explain the reason for any recommended
change, and include supporting data. The FAA will consider all comments received by the closing
date and may amend this final rule because of those comments.
Except for Confidential Business Information (CBI) as described in the following paragraph, and
other information as described in 14 CFR 11.35, the FAA will post all comments received, without
change, to https://www.regulations.gov, including any personal information you provide. The agency
will also post a report summarizing each substantive verbal contact received about this final rule.

Confidential Business Information

CBI is commercial or financial information that is both customarily and actually treated as
private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt
from public disclosure. If your comments responsive to this AD contain commercial or financial
information that is customarily treated as private, that you actually treat as private, and that is
relevant or responsive to this AD, it is important that you clearly designate the submitted comments
as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat
such marked submissions as confidential under the FOIA, and they will not be placed in the public
docket of this AD. Submissions containing CBI should be sent to Brett Portwood, Continued
Operational Safety Technical Advisor, COS Program Management Section, Operational Safety
Branch, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 817-222-5390; email:
operationalsafety@faa.gov. Any commentary that the FAA receives that is not specifically
designated as CBI will be placed in the public docket for this rulemaking.

Regulatory Flexibility Act

The requirements of the Regulatory Flexibility Act (RFA) do not apply when an agency finds
good cause pursuant to 5 U.S.C. 553 to adopt a rule without prior notice and comment. Because the
FAA has determined that it has good cause to adopt this rule without notice and comment, RFA
analysis is not required.

Impact on Intrastate Aviation in Alaska

For the reasons discussed above, this AD will not affect intrastate aviation in Alaska.

Costs of Compliance

The FAA estimates that this AD affects 6,834 airplanes of U.S. registry. The FAA estimates the
following costs to comply with this AD:

5
 Estimated Costs
Action Labor cost Parts Cost per Cost on U.S.
cost product operators
AFM 1 work-hour × $85 per hour = $0 $85 $580,890
revision $85

As previously discussed, there may be other impacts to aviation; however there remains
uncertainty as to cost due to various factors such as which airports within the United States have, or
will have, base stations or other devices that could interfere with aircraft radio altimeters.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety.
Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation
Programs describes in more detail the scope of the Agency's authority.
The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart
III, Section 44701: General requirements. Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices,
methods, and procedures the Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it addresses an unsafe condition that is likely
to exist or develop on products identified in this rulemaking action.

Regulatory Findings

This AD will not have federalism implications under Executive Order 13132. This AD will not
have a substantial direct effect on the States, on the relationship between the national government and
the States, or on the distribution of power and responsibilities among the various levels of
government.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

The Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR
part 39 as follows:

PART 39–AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

§ 39.13 [Amended]

2. The FAA amends § 39.13 by adding the following new airworthiness directive:

6
 AIRWORTHINESS
FAA DIRECTIVE
Aviation Safety
www.faa.gov/aircraft/safety/alerts/
www.gpoaccess.gov/fr/advanced.html

2021-23-12 Transport and Commuter Category Airplanes: Amendment 39-21810; Docket No.
FAA-2021-0953; Project Identifier AD-2021-01169-T.

(a) Effective Date

This airworthiness directive (AD) is effective December 9, 2021.

(b) Affected ADs

None.

(c) Applicability

This AD applies to all transport and commuter category airplanes equipped with a radio (also
known as radar) altimeter. These radio altimeters are installed on various transport and commuter
category airplanes including, but not limited to, the airplanes for which the design approval holder is
identified in paragraphs (c)(1) through (19) of this AD.

(1) The Boeing Company

(2) Airbus SAS
(3) Bombardier Inc.
(4) Embraer S.A.
(5) Gulfstream Aerospace Corporation
(6) Gulfstream Aerospace LP
(7) Textron Aviation Inc.
(8) Pilatus Aircraft Limited
(9) Fokker Services B.V.
(10) Saab AB, Support and Services
(11) DeHavilland Aircraft of Canada Limited
(12) Airbus Canada Limited Partnership
(13) ATR-GIE Avions de Transport Régional
(14) Yaborã Ind[uacute]stria Aeronáutica S.A.
(15) MHI RJ Aviation ULC
(16) BAE Systems (Operations) Limited
(17) Lockheed Martin Corporation/Lockheed Martin Aeronautics Company
(18) Viking Air Limited
(19) Dassault Aviation

(d) Subject

Air Transport Association (ATA) of America Code 31, Indicating/Recording System; 34,
Navigation.

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(e) Unsafe Condition

This AD was prompted by a determination that radio altimeters cannot be relied upon to perform
their intended function if they experience interference from wireless broadband operations in the 3.7-
3.98 GHz frequency band (5G C-Band). The FAA is issuing this AD because radio altimeter
anomalies that are undetected by the automation or pilot, particularly close to the ground (e.g.,
landing flare), could lead to loss of continued safe flight and landing.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Airplane/Aircraft Flight Manual (AFM) Revision

On or before January 4, 2022: Revise the Limitations Section of the existing AFM by
incorporating the limitations specified in figure 1 to paragraph (g) of this AD. This may be done by
inserting a copy of this AD into the existing AFM.

(h) Alternative Methods of Compliance (AMOCs)

(1) The Manager, Operational Safety Branch, FAA, has the authority to approve AMOCs for this
AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19,
send your request to your principal inspector or responsible Flight Standards Office, as appropriate. If
sending information directly to the manager of the Operational Safety Branch, send it to the attention
of the person identified in paragraph (i) of this AD. Information may be emailed to: AMOC@faa.gov.
(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a
principal inspector, the manager of the responsible Flight Standards Office.

(i) Related Information

For more information about this AD, contact Brett Portwood, Continued Operational Safety
Technical Advisor, COS Program Management Section, Operational Safety Branch, FAA, 3960

8
Paramount Boulevard, Lakewood, CA 90712-4137; phone: 817-222-5390; email:
operationalsafety@faa.gov.

(j) Material Incorporated by Reference

None.

Issued on December 7, 2021.

Gaetano A. Sciortino,
Deputy Director for Strategic Initiatives, Compliance & Airworthiness Division, Aircraft
Certification Service.
[FR Doc. 2021-26777 Filed 12-7-21; 2:00 pm]