[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]


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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.

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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.

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: [email protected].

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.
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    \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''
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    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\
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    \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.
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    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 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

[[Page 69985]]

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.
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    \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.
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    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 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.
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    \6\ The FAA's process for issuing NOTAMs is described in FAA 
Order 7930.2S, Notices to Air Missions (NOTAM), December 2, 2021.
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    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

[[Page 69986]]

rule because radio altimeter anomalies that are undetected by the 
aircraft automation or pilot, particularly close to the ground (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: 
[email protected]. 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:

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

0
1. The authority citation for part 39 continues to read as follows:

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


Sec.  39.13   [Amended]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive:

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.

[[Page 69987]]

(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 R[eacute]gional
(14) Yabor[atilde] Ind[uacute]stria Aeron[aacute]utica 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.

(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.
[GRAPHIC] [TIFF OMITTED] TR09DE21.007

(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: [email protected].
    (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 Paramount 
Boulevard, Lakewood, CA 90712-4137; phone: 817-222-5390; email: 
[email protected].

(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]
BILLING CODE 4910-13-P


