[Federal Register Volume 88, Number 102 (Friday, May 26, 2023)]
[Rules and Regulations]
[Pages 34065-34081]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-11371]



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 Rules and Regulations
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  Federal Register / Vol. 88 , No. 102 / Friday, May 26, 2023 / Rules 
and Regulations  

[[Page 34065]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2022-1647; Project Identifier AD-2022-01379-T; 
Amendment 39-22438; AD 2023-10-02]
RIN 2120-AA64


Airworthiness Directives; Transport and Commuter Category 
Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2021-23-
12, which applied to all transport and commuter category airplanes 
equipped with a radio (also known as radar) altimeter. AD 2021-23-12 
required 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). Since the FAA issued AD 2021-23-12, the FAA determined that 
additional limitations are needed due to the continued deployment of 
new 5G C-Band stations whose signals are expected to cover most of the 
contiguous United States at transmission frequencies between 3.7-3.98 
GHz. For certain airplanes, this AD requires revising the limitations 
section of the existing AFM to incorporate limitations prohibiting 
certain operations requiring radio altimeter data, due to the presence 
of 5G C-Band interference. This AD also requires modifying certain 
airplanes to allow safe operations in the U.S. 5G C-Band radio 
frequency environment. The FAA is issuing this AD to address the unsafe 
condition on these products.

DATES: This AD is effective May 26, 2023.

ADDRESSES: AD Docket: You may examine the AD docket at regulations.gov 
under Docket No. FAA-2022-1647; 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 address for Docket Operations is 
U.S. Department of Transportation, Docket Operations, M-30, West 
Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, 
Washington, DC 20590.

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

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 to supersede AD 2021-23-12, Amendment 39-21810 (86 FR 
69984, December 9, 2021) (AD 2021-23-12). AD 2021-23-12 applied to all 
transport and commuter category airplanes equipped with a radio (also 
known as radar) altimeter. The NPRM published in the Federal Register 
on January 11, 2023 (88 FR 1520). The NPRM was prompted by the 
determination that radio altimeters cannot be relied upon to perform 
their intended function if they experience 5G C-Band interference.
    In the NPRM, the FAA proposed to maintain the requirements of AD 
2021-23-12, except for the limitations pertaining to Required 
Navigation Performance with Authorization Required (RNP AR) instrument 
approach procedures (IAPs), by requiring revising the existing AFM to 
incorporate limitations prohibiting certain operations in the presence 
of 5G C-Band wireless broadband interference as identified by NOTAM. 
Alternatively, the FAA proposed to allow operators to retain the AFM 
revision required by paragraph (g) of AD 2021-23-12. The FAA also 
proposed, on or before June 30, 2023, to require revising the existing 
AFM to incorporate limitations prohibiting these same operations at all 
airports for non-radio altimeter tolerant airplanes. For radio 
altimeter tolerant airplanes, the prohibited operations would be 
allowed at 5G C-Band mitigated airports (5G CMAs) as identified in an 
FAA Domestic Notice.
    Lastly, the FAA proposed, on or before February 1, 2024, to require 
that airplanes operating under 14 CFR part 121 be modified from a non-
radio altimeter tolerant airplane to a radio altimeter tolerant 
airplane. The FAA proposed 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. Additionally, radio altimeter anomalies could lead 
to increased flightcrew workload and flightcrew desensitization to 
warnings.

Discussion of Final Airworthiness Directive

Comments

    The FAA provided the public with an opportunity to comment on the 
proposed AD and received 82 submissions to Docket No. FAA-2022-1647. 
The FAA received comments from individual commenters as well as from 
organizations. The majority of the comments were from organizations 
such as the International Air Transport Association (IATA), Airlines 
for America (A4A), the Cargo Airline Association, the Aerospace 
Industries Association (AIA), the Air Line Pilots Association, 
International (ALPA), the Allied Pilots Association, the Regional 
Airline Association (RAA), CTIA-The Wireless Association (CTIA), and 
the American Association of Airport Executives (AAAE); manufacturers 
such as Airbus DS (Airbus Defence and Space), Airbus SAS (Airbus), The 
Boeing Company (Boeing), MHI RJ Aviation ULC (MHI RJ), Gulfstream 
Aerospace Corporation (Gulfstream), Bombardier Inc. (Bombardier), 
Textron Aviation (Textron), and Thales; and operators such as Atlas 
Air, Inc. (Atlas), Frontier Airlines (Frontier), Southwest Airlines, 
and Virgin Atlantic Airways.
    The following summarizes the comments received on the NPRM, and 
provides the FAA's responses.

A. Support for the NPRM

    CTIA supported the NPRM without change.

[[Page 34066]]

B. Alternative Methods of Compliance (AMOCs)

1. Request for Continued NOTAMs and AMOCs
    Comment summary: Some commenters asked if the FAA will continue 
approving AMOCs for radio altimeter tolerant airplanes at non-5G CMAs 
consistent with the process used for AD 2021-23-12. Airbus Defence and 
Space asked whether the FAA will still allow AMOCs between July 1, 
2023, and January 31, 2024. One commenter asked whether the FAA will 
take into account the availability of a certified solution before 
ceasing to process new AMOCs and, if not, when will FAA stop processing 
AMOCs for non-radio altimeter tolerant airplanes. Other commenters 
requested that the FAA continue to use NOTAMs and AMOCs until relevant 
airplanes are retrofitted. Airbus asked when the FAA will stop issuing 
NOTAMs for identification of the 5G environment.
    FAA response: Since the publication of the NPRM, the FAA has 
conducted further analysis of possible 5G C-Band interference to radio 
altimeter tolerant airplanes at non-5G CMAs and has determined that the 
risks associated with category (CAT) I autoland, CAT I head-up display 
(HUD) to touchdown, and enhanced flight vision system (EFVS) to 
touchdown operations, are mitigated to an acceptable level. The FAA 
found a lower-than-expected likelihood of interference because of 
current tower locations, a high percentage of flat terrain around 
airports, and the expectation that future tower locations will impose 
no additional interference than current towers do. Risks associated 
with CAT II/III, SA CAT I, and SA CAT II have been mitigated at non-5G 
CMAs because all current CAT II/III and SA CAT I/II operations are only 
at 5G CMAs.\1\ Therefore, the FAA has determined that radio altimeter 
tolerant airplanes may conduct these operations to all airports in the 
contiguous U.S. without limitation.\2\ As a result, there is no need to 
use a domestic notice to identify specific airports where radio 
altimeter tolerant airplanes can perform these procedures. The FAA has 
removed the references to 5G CMAs and Domestic Notices from the 
regulatory requirements of this final rule.
---------------------------------------------------------------------------

    \1\ Locations of 5G CMAs can be found on the FCC's website at: 
https://www.fcc.gov/ecfs/search/search-filings/filing/1033142661477.
    \2\ This determination applies only to the unsafe condition 
identified in this AD, and not to the model-specific unsafe 
conditions addressed in AD 2022-02-16, AD 2022-03-05, AD 2022-03-20, 
AD 2022-04-05, AD 2022-05-04, AD 2022-06-16, AD 2022-09-18, AD 2023-
03-06, and AD 2023-06-13. Copies of those ADs may be found on the 
FAA's Dynamic Regulatory System website at www.drs.faa.gov.
---------------------------------------------------------------------------

    NOTAMs identifying the 5G environment are no longer practical 
because the environment is expected to cover most of the contiguous 
U.S. In addition, limitations required by this AD apply to non-radio 
altimeter tolerant airplanes at all airports in the contiguous U.S. For 
those airplanes, the FAA has determined that the AMOC process used for 
AD 2021-23-12, which included generating monthly cleared runway lists 
based on base station data for non-5G CMAs, will be untenable beyond 
June 30, 2023, due to complexities associated with the continued 
operational expansion of 5G C-Band emissions.
2. Request for Alternative Mitigation
    Comment summary: Thales requested that the proposed AD be revised 
to allow for other mitigations at the airplane level, based on 
airplane-level architecture, including alerts and crew procedures 
related to radio altimeter NCD (no computed data) or failure. Thales 
stated that radio altimeter compliance with the tolerances specified in 
paragraphs (g)(2)(i) and (ii) of the proposed AD is not the only way to 
prevent the unsafe condition. Additionally, Airbus Defence and Space 
stated that it expected stronger operations limitations for non-radio 
altimeter tolerant airplanes, rather than full prohibition of the 
operations.
    FAA response: Although the FAA acknowledges that there may be other 
ways to prevent the unsafe condition, the alternatives proposed by the 
commenters must be evaluated on a case-by-case basis to determine an 
acceptable level of safety. Because including such language to address 
all airplane type designs would not be feasible in this AD, anyone may 
propose alternative actions to address the unsafe condition under the 
AMOC procedures referenced in paragraph (k) of this AD.
3. Request To Clarify Credit for Prior AMOCs
    Comment summary: Bombardier stated that the existing AMOC 
methodology remains valid, and therefore radio altimeter/airplane 
configurations that receive approved AMOCs for 5G CMAs in June 2023 
would meet the definition of radio altimeter tolerant airplanes. 
Bombardier requested that the FAA clarify whether an FAA-approved AMOC 
for AD 2021-23-12 is a ``method approved by the FAA'' for demonstrating 
that an airplane is a radio altimeter tolerant airplane for purposes of 
the AFM limitations that would otherwise be required by paragraph (i) 
of the proposed AD.
    FAA response: In the NPRM, the FAA proposed that AMOCs approved for 
AD 2021-23-12 would only be approved for the AFM revision in paragraph 
(h) of the proposed AD. The FAA approved AMOCs for AD 2021-23-12 before 
the radio altimeter tolerant PSD (power spectral density) curve 
proposed in the NPRM was defined. Although the FAA expects that the 
airplanes with AMOCs approved for AD 2021-23-12 will be able to meet 
the definition of ``radio altimeter tolerant airplane,'' operators will 
need to provide the FAA with data showing explicitly that the airplane 
meets the tolerances in paragraph (g)(2) before the FAA will approve 
the method they propose to use.

C. AFM Limitations

1. Request To Change AFM Limitations
    Comment summary: Frontier requested that the AD include language 
allowing operators to omit any portion of the radio altimeter flight 
restrictions that is not applicable to the operator, such as HUD and 
EFVS. Frontier stated that this would eliminate confusion when the 
specified equipment is not installed in the airplane or the operator is 
not authorized to utilize the equipment.
    FAA response: The FAA disagrees, as operators may change or add 
equipment and approvals at a future time. If an airplane is not 
equipped or approved for an approach, then the operational restrictions 
would still broadly apply, but would have no impact to the operator.
2. AFM Limitations Inappropriate for General Operational Restrictions
    Comment summary: MHI RJ and Air Wisconsin Airlines stated that the 
AFM limitations section was not the appropriate area to document 
operational restrictions not related to a specific airplane. An 
individual commenter suggested that the proposed AFM revision does not 
follow ``FAA AFM criteria.'' Gulfstream stated that the proposed 
requirement to revise the AFM with limitations places an unnecessary 
burden on original equipment manufacturers (OEMs). Gulfstream requested 
that instead the FAA require that operators obtain Letters of 
Authorization or operations specifications.
    FAA response: The FAA disagrees. 14 CFR 91.9 prohibits any person 
from operating a civil aircraft without complying with the operating 
limitations specified in the AFM. The FAA routinely issues ADs to 
mandate

[[Page 34067]]

changes to the limitations section of an FAA-approved AFM for airplanes 
in service.
3. Requests for Different Method of Incorporating AFM Limitations
    Comment summary: Bombardier and Gulfstream requested the FAA allow 
other options for incorporating the proposed limitations into the AFM, 
due to the complexity of updating entire catalogs of flight manual 
documentation and authoring, approving, and publishing customized 
limitations based on the unique configuration and characteristics of 
each airplane model. Specifically, Bombardier requested that the AD 
include language to automatically delegate approval of AFM changes to 
civil aviation authorities; automatically recognize AFM changes that 
have been approved by Transport Canada Civil Aviation Authority for 
Bombardier airplane models; and state that airplanes with specific AFM 
revisions meet the intent of the proposed AD. Lastly, Bombardier 
requested that the proposed AD allow compliance by either incorporating 
or referencing an electronic or paper copy of the AD, since Bombardier 
plans on making an electronic copy of the FAA AD available through the 
Bombardier flight deck application's supplemental documents function.
    FAA response: The FAA acknowledges that each owner/operator may 
have a different method for incorporating revisions into the AFM for 
its airplanes. This is why the FAA did not propose a specific method of 
complying with this requirement. As long as the language added to the 
limitations section of the AFM is identical to the language specified 
in the applicable figure, owners/operators may make the revision 
electronically, with pen-and-ink changes, by inserting a copy of the 
AD, by inserting a copy of the applicable figure, by adopting the OEM's 
AFM revision, or by any other method. To provide clarification, the FAA 
has changed paragraphs (h), (i)(1), and (j)(1) of this AD to require 
including ``the information'' specified in the figure instead of ``the 
limitations'' specified in the figure. With regard to Bombardier's 
request that the proposed AD be revised to state that Bombardier 
airplanes meet the intent of paragraph (h) of this AD if they have 
incorporated certain AFM revisions, the FAA disagrees. Although the 
requested changes to the proposed AD may minimize some requests for 
AMOC approvals, including language specific to all possible current and 
future state-of-design 5G C-Band-related ADs, is out of the scope of 
the intent of this AD.
    Comment summary: In order to minimize unnecessary revisions to the 
AFM language in the future, Bombardier asked the FAA to clarify why the 
flight restrictions in the figures required by June 30, 2023, are 
limited to the contiguous U.S. airspace and whether the situation will 
evolve as various telecommunications companies deploy 5G services in 
the C-Band outside the contiguous U.S.
    FAA response: The FAA limited the flight restrictions in the 
proposed figures to the contiguous U.S. based on Federal Communications 
Commission (FCC) Report and Order FCC 20-22,\3\ which identifies radio 
frequencies and power level conditions for the new C-Band services only 
in the contiguous lower-48 states. In the event the FCC updates the 
report and order to include additional states and U.S. territories, the 
FAA might consider future rulemaking.
---------------------------------------------------------------------------

    \3\ 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-2022-1647, and at https://www.fcc.gov/document/fcc-expands-flexible-use-cband-5g-0.
---------------------------------------------------------------------------

D. Effect of Winglets on Accomplishment of the Proposed Actions

    Comment summary: Aviation Partners Boeing stated that installing 
winglets under supplemental type certificate (STC) ST00830SE, STC 
ST01219SE, STC ST01518SE, and STC ST01920SE on applicable Boeing models 
does not affect accomplishment of the actions specified in the proposed 
AD.
    FAA response: The FAA agrees. The FAA has not changed this AD in 
this regard.

E. Clarifications

1. Request To Clarify Terminology
    Comment summary: In the NPRM preamble, the FAA explained that if 
the unsafe condition is not addressed, it may result in a catastrophic 
accident, incident, or event. Airbus stated that because 
``catastrophic'' is part of the analysis conducted under 14 CFR 
25.1309, the FAA's use of it in the NPRM could be misleading. Textron 
requested that the FAA add language to the unsafe condition statement 
in paragraph (e) of the proposed AD to clarify the severity of possible 
failure conditions (catastrophic, hazardous) associated with 5G C-Band 
interference.
    FAA response: The FAA used the term ``catastrophic'' in the 
preamble of the NPRM to indicate an event that would result in multiple 
fatalities, usually with loss of the airplane. The unsafe condition 
statement in paragraph (e) of this AD, which states that radio 
altimeter anomalies could result in loss of continued safe flight and 
landing or increased flightcrew workload and desensitization to 
warnings, is sufficiently clear. No change to this AD is necessary 
based on these comments.
2. Request To Clarify Relaxation on Non-Precision Approaches (NPAs) to 
Certain Airports
    Comment summary: Qatar Airways referenced the statement in the NPRM 
that the proposed AD would no longer prohibit RNP AR IAPs and asked 
whether the FAA was relaxing NPAs for non-radio altimeter-tolerant 
airplanes other than RNP AR operations to airports with potential 5G C-
Band interference.
    FAA response: NPAs were not included in the list of prohibited 
operations in AD 2021-23-12, since an NPA is an instrument approach 
that provides lateral guidance only, and does not rely on radio 
altimeter inputs. Therefore, this AD does not address NPAs.
3. Request To Clarify Whether Compliance With AD 2021-23-12 Satisfies 
AFM Revision Requirement
    Comment summary: Qatar Airways asked the FAA to clarify the 
statement in paragraph (h) of the proposed AD that ``If an operator has 
complied with paragraph (g) of AD 2021-23-12, that action satisfies the 
requirements of this paragraph.'' The commenter noted that RNP AR IAPs 
are included in the list of prohibited operations in paragraph (g) of 
AD 2021-23-12; however, the NPRM states that, after further FAA 
analysis, those operations would no longer be prohibited by the 
proposed AD.
    FAA response: The commenter is correct that the prohibition in 
paragraph (g) of AD 2021-23-12 includes RNP AR approaches, and the 
prohibition in paragraph (h) of this AD does not. However, since all of 
the requirements of paragraph (h) of this AD are included in paragraph 
(g) of AD 2021-23-12, operators have the option of retaining the AFM 
revision required AD 2021-23-12 instead of revising the AFM again to 
comply with paragraph (h) of this AD even though it prohibits RNP AR 
approaches that are not required by this AD. No change to this AD is 
necessary based on this comment.
4. Request To Clarify Limitations for Tolerant and Non-Tolerant 
Airplanes
    Comment summary: Singapore Airlines, Airbus Defence and Space, 
Airbus, Qatar Airways, AIA, AFR, and Air France requested clarification 
of the limitations for radio altimeter tolerant

[[Page 34068]]

airplanes and non-radio altimeter tolerant airplanes, as related to 5G 
CMAs and non-5G CMAs. Airbus also requested clarification regarding 
retrofitting with a 5G tolerant radio altimeter and the effect of a 
future technical standard order (TSO).
    FAA response: In the NPRM, the FAA proposed that radio altimeter 
tolerant airplanes could perform the otherwise prohibited operations at 
5G CMAs, while non-radio altimeter tolerant airplanes would be 
prohibited from performing those operations at all airports. As 
explained in section B.1. of this final rule, since the NPRM was 
published, the FAA has determined that radio altimeter tolerant 
airplanes may perform the prohibited operations at all airports in the 
contiguous U.S., as long as the telecommunications companies continue 
to transmit within mitigated parameters.\4\ As a result, the FAA has 
removed paragraph (j) of the proposed AD from this final rule. The 
FAA's determination that non-radio altimeter tolerant airplanes will 
not be able to safely perform the four prohibited operations at any 
airport remains unchanged.
---------------------------------------------------------------------------

    \4\ A copy of the letter from AT&T, Verizon, T-Mobile, and 
UScellular dated March 31, 2023, documenting their voluntary 
commitments to transmit within mitigated parameters (hereinafter 
referred to as ``voluntary commitments'' or ``voluntary agreement 
letter dated March 31, 2023'') is in Docket No. FAA-2022-1647 and 
can be found on the FCC's website at: https://www.fcc.gov/ecfs/search/search-filings/filing/1033142661477.
---------------------------------------------------------------------------

    Some radio altimeters may already demonstrate tolerance to 5G C-
Band emissions without modification. Some may need to install filters 
between the radio altimeter and antenna to increase a radio altimeter's 
tolerance. For others, the radio altimeter will need to be replaced 
with an upgraded radio altimeter as established by a new radio 
altimeter TSO, which will follow the existing international technical 
consensus on the establishment of the minimum operational performance 
standards (MOPS). The FAA considers this AD an interim action because 
additional rulemaking may be necessary once a new radio altimeter TSO 
is developed, approved, and available.
5. Request To Clarify Multiple AFM Limitations
    Comment summary: Textron asked the FAA to clarify the relationship 
between the AFM limitation requirements in paragraphs (h) and (i) of 
the proposed AD.
    FAA response: As explained in section B.1. of this final rule, 
since the NPRM was published, the FAA has determined that radio 
altimeter tolerant airplanes may perform the prohibited operations at 
all airports in the contiguous U.S. As a result, the FAA has revised 
this AD so that all of the AFM revisions are required only for non-
radio altimeter tolerant airplanes. Those airplanes must incorporate 
either the limitations in paragraph (h) of this AD or paragraph (g) of 
AD 2021-23-12 until June 30, 2023. After June 30, 2023, non-radio 
altimeter tolerant airplanes must replace those limitations with the 
limitations in paragraph (i) of this AD. For operators of radio 
altimeter tolerant airplanes, this AD terminates the AFM limitations 
required by AD 2021-23-12.
6. Request To Clarify Applicability for Military Airplanes
    Comment summary: The Department of Defense requested that the FAA 
revise the NPRM to clarify that military aircraft, including civil 
derivatives, are exempt. The commenter stated that the NPRM's reference 
to part 121 operations creates confusion as to whether the AD applies 
to civil derivative airplanes operated by the Department of Defense.
    FAA response: The FAA disagrees. This AD applies to all airplanes 
with an FAA type certificate in the transport or commuter category, 
including military surplus airplanes and civil derivatives of military 
airplanes. To the extent that the AFM revisions required by this AD 
impose operational restrictions that apply only to civil aircraft, 
those restrictions do apply to Department of Defense airplanes used in 
civil operations in the national airspace system.
7. Factors Affecting Accomplishment of Required Actions
    Comment summary: AIA requested that the NPRM preamble be revised to 
acknowledge that quickly accomplishing alterations depends on many 
factors, including adequate specification of the replacement equipment 
and availability of updated equipment.
    FAA response: The FAA acknowledges that factors including those 
cited by the commenter impact the ability to accomplish the 
modification of the radio altimeters as required by this AD. Since the 
language from the NRPM that the commenter cited does not appear in this 
final rule, no change to the AD is necessary.

F. 5G CMAs

    Comment summary: The FAA received many comments concerning the 
airports that will be included as a 5G CMA. All Nippon Airways 
requested the FAA establish a system that allows radio altimeter 
tolerant airplanes to operate at all U.S. airports without 
restrictions. MHI RJ, Thales, Airbus, Qatar Airlines, Japan Airlines, 
ALPA, and two individual commenters asked for information about the 
list of 5G CMAs. Aerologic, Emirates Airline, Atlas, the Department of 
Defense, and the Cargo Airline Association requested the FAA expand the 
list to include as many airports as possible. Multiple commenters, 
including A4A, Boeing, Airbus, AIA, ALPA, RAA, and the Cargo Airline 
Association, requested clarification of the criteria used to determine 
the 5G CMAs. Thales, Airbus, Allied Pilots Association, AIA, ALPA, 
Gulfstream, and AAAE requested guidance for safe aviation operations at 
non-5G CMAs.
    FAA response: As mentioned in section B.1. of this final rule, 
since the NPRM was published, the FAA conducted further analysis of 
possible 5G C-Band interference with radio altimeter tolerant airplanes 
and determined that radio altimeter tolerant airplanes are not 
susceptible to the 5G C-Band interference this AD is addressing. 
Therefore, this AD will not require operators of radio altimeter 
tolerant airplanes to revise their AFM to prohibit the low-visibility 
operations proposed in the NPRM. The FAA has revised this final rule 
accordingly.

G. Compliance Time

    Comment summary: While CTIA agreed with the FAA's proposed 
compliance times, China Airlines, SkyWest Airlines, Embraer S.A., 
Airbus Defence and Space, the Association of Asia Pacific Airlines, 
Qatar Airways, Endeavor Air, Virgin Atlantic Airways, Atlas Air, ATR, 
Gulf Air Group, the Cargo Airline Association, Air Wisconsin Airlines, 
Lynden Air Cargo, EVA Airways, AAAE, A4A, RAA, and an individual 
commenter expressed concern, with many stating that modification of the 
fleet would not be achievable by June 30, 2023, or by February 1, 2024. 
The commenters requested extensions ranging from three months to two 
years, based on the size of each operator's fleet and availability of 
parts.
    FAA response: The FAA carefully considered the impact of the loss 
of low-visibility operations on the remaining unmodified fleet after 
June 30, 2023, and did not take the decision to prohibit these 
operations lightly. The June 30, 2023, date was driven by the unsafe 
condition over which the FAA has no control. After refraining from 
operating at their FCC-authorized levels for a year and a half, 
wireless companies are now able to operate at higher levels, yet still 
not at the levels authorized.

[[Page 34069]]

Specifically, wireless companies expect to operate their networks in 
urban areas with minimal restrictions due to the completion of 
retrofits.\5\ Additionally, the FAA anticipates 19 additional 
telecommunication companies will begin transmitting in the C-Band after 
June 30, 2023. Although the FAA continues to work with the companies 
that intend to transmit in the 3.7-3.98-GHz band near 5G CMAs, the FAA 
has no agreement with those companies to provide the FAA with tower 
locations and other information necessary to support the current NOTAM/
AMOC process. Therefore, the FAA will not be able to extend the June 
30, 2023, date.
---------------------------------------------------------------------------

    \5\ See the FAA website faa.gov/newsroom/faa-statements-5g.
---------------------------------------------------------------------------

    The FAA re-evaluated the February 1, 2024, date based on the latest 
radio altimeter equipage data and determined that an extension is not 
justified. The only airplanes operating under part 121 that are 
forecast to be at risk of not being equipped by February 1, 2024, are 
approximately 164 transport category airplanes that have older radio 
altimeters with no support from the airplane OEMs or radio altimeter 
manufacturers. Operators of those airplanes will need to make a 
business decision to equip with later model radio altimeters or retire 
those airplanes from part 121 operations, as after February 1, 2024, 
this AD prohibits unmodified airplanes from operating under part 121 in 
the contiguous U.S. The FAA and its foreign civil aviation authority 
partners plan to expedite radio altimeter approvals for both part 121 
and part 129 operators, and the FAA has used means such as approved 
model list (AML) STCs to help with equipage.
    In addition, because some airplanes operate under part 121 solely 
outside of the contiguous U.S. airspace where the AD's requirements do 
not apply, the FAA has revised figure 4 to paragraph (i) of this AD to 
include a prohibition that states, ``As of February 1, 2024, [non-radio 
altimeter tolerant airplanes] must not operate under 14 CFR part 121 in 
the contiguous U.S.'' The FAA has also revised paragraph (k) of the 
NPRM (paragraph (j) of this AD) from a modification requirement to a 
terminating action for airplanes that have been modified to radio 
altimeter tolerant airplanes by allowing for the removal of the 
limitations from the AFM.

H. Costs

1. Small Business Status for Business Airplanes
    Comment summary: One commenter stated that the vast majority of 
business airplane operators under part 91 are small businesses as 
defined by the Small Business Administration (SBA). The commenter 
requested that the FAA not underestimate the choice small businesses 
will have to make between an $80,000 retrofit and loss of utility of 
the airplane during adverse weather conditions.
    FAA response: The FAA has complied with the Regulatory Flexibility 
Act for this AD and analyzed its impact on small businesses. However, 
the FAA has identified an unsafe condition for which the agency could 
not identify an appropriate alternative that sufficiently addresses the 
safety problem. Further information regarding that analysis is provided 
in section 2. of the Regulatory Flexibility Determination of the 
preamble of this final rule.
2. Costs Underestimated for Legacy Airplanes
    Comment summary: Lynden Air Cargo commented that the NPRM 
underestimates the cost of modification for legacy airplanes that are 
no longer in the ``as-delivered'' configuration and therefore lack 
support from the OEM. The commenter stated there are significant costs 
associated with the research and development, approval, and type design 
amendment for new equipment.
    FAA response: The FAA acknowledges that the certification cost is 
not included in the estimate in this final rule. The FAA appreciates 
the impact on operators of legacy fleets that do not have the support 
of the airplane OEM. The FAA has been issuing letters accepting 5G C-
Band-resistant test data from the holders of TSO authorizations (TSOAs) 
in order to assist independent entities in seeking approval in 
situations like these to mitigate the cost impact. These letters are 
available through the TSOA holders.
    Regarding Lynden Air Cargo's comment on additional significant 
costs, that comment is addressed in section 2. of the Regulatory 
Flexibility Determination in the preamble of this AD. The FAA did not 
change this AD as a result of this comment.
3. Request To Include Indirect Costs
    Comment summary: Some commenters requested that FAA include costs 
associated with development and certification, as well as with 
operational impacts of the proposed AD such as delayed and canceled 
flights.
    FAA response: These comments are addressed in section 2. of the 
Regulatory Flexibility Determination in the preamble of this AD. The 
FAA did not change this AD as a result of these comments.
4. Request To Consider Costs for Non-Part 121 Operations
    Comment summary: Textron commented that the FAA's estimated costs 
almost exclusively addressed part 121 operations. Textron asked whether 
airplanes that do not operate under part 121 are affected by the 
prohibited operations and requested that the FAA include those 
airplanes in the cost analysis.
    FAA response: While part 121 operators own most of the affected 
airplanes and bear the greatest cost associated with this AD, the FAA 
is aware of the impact on other operators who choose not to modify 
their airplanes to become radio altimeter tolerant. Regarding Textron's 
request to include the cost of the impact of restricted operations for 
those airplanes, that comment is addressed in section 2. of the 
Regulatory Flexibility Determination in the preamble of this AD. The 
FAA did not change this AD as a result of these comments.
5. Work-Hours Underestimated for AFM Updates
    Comment summary: Bombardier and an individual stated that the 
estimated cost of 1 work-hour per airplane at $85 per hour for revising 
an AFM was too low.
    FAA response: These comments are addressed in section 2. of the 
Regulatory Flexibility Determination in the preamble of this AD. The 
FAA did not change this AD as a result of these comments.
6. Cost Impact on Part 129 Operators
    Comment summary: IATA stated the FAA's cost estimate is vastly 
understated because it does not include costs for airplanes operating 
under part 129. Ten other commenters agreed with IATA's comments.
    FAA response: Although the FAA acknowledges and appreciates the 
costs of retrofit for part 129 operators, the FAA did not include costs 
for airplanes operating under part 129 because this AD does not impose 
any requirements on non-U.S. registered airplanes operating into the 
United States under part 129. Under International Civil Aviation 
Organization (ICAO) Annex 8, Airworthiness of Aircraft, the state of 
registry of an airplane is the state responsible for its airworthiness. 
For this reason, FAA ADs apply only to U.S.-registered airplanes.

[[Page 34070]]

7. Inquiry Regarding Payment for Additional Upgrades
    Comment summary: Emirates requested that, in the event additional 
upgrades are needed due to the telecommunications companies not 
following their voluntary agreements, the telecommunications companies 
should be responsible for the cost of the upgrades.
    FAA response: The FAA, as a federal agency, is responsible for all 
directives, policies, and mandates issued under its authority. The FAA 
does not have the authority to require telecommunications companies to 
bear costs incurred in modifying privately owned aircraft.
8. Request To Revise Costs for Filters
    Comment summary: SkyWest Airlines requested that the FAA re-
evaluate the part and labor costs for filter installation.
    FAA response: This comment is addressed in section 2. of the 
Regulatory Flexibility Determination in the preamble of this final 
rule.
9. Request To Revise Cost Estimate Including Equipment To Meet Tolerant 
Criteria
    Comment summary: Airbus and the Cargo Airline Association stated 
the FAA's cost estimate is too low. These commenters requested that the 
FAA reconsider the cost estimate, including conducting a regulatory 
evaluation, but did not provide cost data. Bombardier requested that 
the FAA include a cost estimate for operators who are not required to 
equip with an updated radio altimeter but chose to voluntarily do so.
    FAA response: The FAA's cost evaluation reflects both a cost per 
product and an estimated fleet cost, which the agency based on feedback 
from airplane manufacturers, radio altimeter manufacturers, and 
airlines. The FAA did conduct a regulatory evaluation in both the NPRM 
and this final rule. Further information regarding that analysis is 
provided in the Regulatory Flexibility Determination section of the 
preamble of this final rule. As explained in section 2. of the 
Regulatory Flexibility Determination, based on feedback from other 
commenters, the FAA has revised some of the cost estimates in this 
final rule.

I. Domestic Notice

    Comment summary: Many commenters expressed concern about the use of 
a Domestic Notice in the proposed AD and the additional burden it would 
create for operators, as there is no routine subscription and 
notification process for Domestic Notices (as there is with NOTAMs). 
British Airways, Qatar Airways, A4A, Boeing, AIA, ALPA, AAAE, and EVA 
Airways requested guidance on the process and revision cycle for the 
FAA 5G C-Band Domestic Notice. Qatar Airways and Virgin Atlantic 
Airways asked how the FAA 5G C-Band Domestic Notice will be 
disseminated to foreign-registered operators.
    FAA response: As explained in section B.1. of this final rule, 
since the NPRM published, the FAA performed additional analysis and 
determined that radio altimeter tolerant airplanes may conduct 
operations at all airports in the contiguous U.S. without the 
limitations imposed by this AD. As a result, there is no need to 
identify specific airports where the radio altimeter tolerant airplanes 
may operate. The FAA has removed the references to the FAA 5G C-Band 
Domestic Notice from the regulatory text of this final rule.

J. FCC Codification

    Comment summary: Many commenters expressed concern that the FAA 
does not have authority to enforce the voluntary agreements between the 
FAA and the telecommunications companies and questioned the possible 
impacts if those companies stop honoring the agreements or change their 
position. Airbus and Bombardier requested the FAA provide additional 
information about the time duration of the agreements. Several of these 
commenters asked the FAA to verify that the additional 19 
telecommunications companies will also voluntarily agree to these 
mitigations. Several commenters urged the FAA, the FCC, and the 
National Telecommunications and Information Administration (NTIA) to 
work together to develop binding long-term agreements. CTIA, however, 
stated that the voluntary and coordinated approach has proven 
successful for this issue so far and noted that the wireless industry 
will continue to engage with the FAA and aviation industry.
    FAA response: The commenters are correct that the agreements 
between the FAA and the telecommunications companies have been 
voluntary because the FAA does not have enforcement authority over the 
companies' use of licenses they receive from the FCC. However, the FAA, 
NTIA, and FCC have worked extensively and collaboratively with the 
licensees to ensure that the agreements confirm necessary notification 
and coordination, that mitigations are in place with network 
deployments, and that the agreements are enforceable by the FCC. These 
March 31, 2023, voluntary agreements allow the FAA to continue to 
address aviation safety by coordinating 5G C-Band effective isotropic 
radiated power (EIRP) reductions when analysis indicates that a 
proposed base station will exceed the permitted PSD values in the 
runway safety zone of a 5G CMA runway, which ensures the FAA can 
protect SA CAT I, SA CAT II, CAT II, and CAT III approach operations 
without limitations.
    The FAA will continue to work with the FCC and NTIA in this regard 
to ensure continuing aviation safety. As stated in the voluntary 
agreement letter dated March 31, 2023, AT&T, T-Mobile, UScellular, and 
Verizon's commitment will last until January 1, 2028, at which point it 
will sunset unless extended or reduced by mutual agreement. A mid-term 
check-in involving the FAA, the FCC, and telecommunications companies 
will occur in July 2026 to assess the status of aviation's long-term 
migration to next-generation radio altimeters and the need for the 
sustainment of these commitments.

K. Special Flight Permit Provisions

    Comment summary: Go Jet Airlines and RAA asked whether the FAA will 
issue special flight permits to allow operators to ferry airplanes to a 
location to perform a radio altimeter upgrade.
    FAA response: As provided in 14 CFR 39.23, the FAA may issue a 
special flight permit to allow operators to fly their airplane to a 
repair facility to perform work required by an AD unless the AD states 
otherwise. Because this AD does not prohibit or limit the issuance of 
special flight permits, they are allowed.

L. Interference Reports

    Comment summary: In the NPRM, the FAA stated it had received over 
420 reports of radio altimeter anomalies within a known location of a 
5G C-Band deployment. Airbus and CTIA requested the FAA provide the 
number of reports of radio altimeter anomalies collected by the FAA in 
the same period of time in a comparable area before the deployment of 
5G base stations. IATA and CTIA requested the FAA share the 
approximately 100 reports of possible radio altimeter interference so 
carriers can better understand and address the unsafe condition. CTIA 
suggested the public would benefit from understanding the connection 
between the data and the nature and scope of any coexistence concerns. 
CTIA further suggested it would be helpful to understand how those 
factors have been evaluated, how often reports in other contexts are 
found to be unattributable, and what findings the FAA makes in those 
other circumstances.

[[Page 34071]]

    FAA response: The FAA received the reports referenced in the NPRM 
from various sources and first determined which reports were associated 
with radio altimeter-related systems in the vicinity of 5G C-Band 
emitters. The FAA then reviewed all supporting information (e.g., 
maintenance data, aircraft and airport trends, and event description), 
and closed reports where the event was due to maintenance, other 
interference, or insufficient data. Because the FAA lacks the means to 
definitively attribute a particular event to 5G C-Band interference, 
the FAA determined that for the remaining events, 5G C-Band 
interference could not be ruled out.
    To the extent some commenters requested comparable data from before 
and after the deployment of 5G C-Band base stations, no such data 
exists. The FAA did not collect 5G C-Band interference report data 
prior to activation of the C-Band. Therefore, a direct comparison is 
not possible.

M. Non-Part 121 Flights

1. Request To Clarify Requirements for Airplanes Not Operating Under 
Part 121
    Comment summary: Numerous commenters asked about the proposed 
requirements for airplanes not operating under part 121. AIA and five 
other commenters asked why the modification is not required for 
airplanes not operating under part 121, as all airplanes will see 
degraded capabilities if the radio altimeter is not retrofitted. 
Singapore Airlines requested that the FAA explain figure 3 to paragraph 
(i) of the proposed AD, and whether airplanes not operating under part 
121 can perform Instrument Landing System (ILS) CAT I IAPs after 
February 1, 2024. Gulfstream and Bahamasair requested clarification of 
the FAA's intent for future rulemaking to impose a modification 
requirement for part 91 and part 135 operators.
    FAA response: After June 30, 2023, this AD prohibits all transport 
and commuter category airplanes, regardless of the type of operation 
(part 91, part 135, part 121, etc.), from performing certain low-
visibility landing operations at any airport (as specified in figure 4 
to paragraph (i) of this AD) unless they have upgraded their radio 
altimeters. Airplanes without upgraded radio altimeters will be able to 
operate into any airport, but cannot fly the prohibited low-visibility 
operations. For airplanes that do not operate under part 121, these 
restrictions, as well as the option to equip with an upgraded radio 
altimeter, remain unchanged after February 1, 2024.
    Only airplanes operating under part 121, in the contiguous U.S., 
must have a 5G C-Band-compatible radio altimeter (or install a 
retrofit) prior to February 1, 2024. The FAA proposed this requirement 
to address the accumulating risk for systems that are less hazardous 
than low-visibility landings (for example, repeated false warnings from 
the collision avoidance system from erroneous radio altimeter data). 
The FAA determined that this accumulating risk will reach unacceptable 
levels for part 121 operations in the contiguous U.S. after February 1, 
2024. The FAA does not anticipate future rulemaking until a TSO 
standard for radio altimeters is established.
2. Request To Clarify Part 129 Requirements
    Comment summary: Eleven commenters asked for clarification of the 
proposed AD with regard to airplanes operating under 14 CFR part 129. 
British Airways, Virgin Atlantic Airways, and Qatar Airways asked the 
FAA to explain the proposed requirements for airplanes operating under 
part 129. The Association of Asia Pacific Airlines requested that the 
FAA extend the proposed compliance date for part 129 operators. Boeing 
requested that the FAA require the proposed modification for part 129 
operators. Singapore Airways commented that the risk and unsafe 
condition described in the NPRM would likely prompt the FAA's foreign 
counterparts to mandate the upgrade to a radio altimeter-tolerant 
airplane when operating in U.S. airspace and asked for clarification 
that non-radio altimeter tolerant airplanes operating under part 129 
could continue to use CAT I ILS approaches after February 1, 2024. 
Airbus Defence and Space asked what the process would be for foreign 
manufacturers and operators if the FAA's foreign counterparts do not 
adopt the FAA's AD. A4A stated concern that the FAA is considering 
different standards for domestic operators versus foreign operators, 
which does not reflect a ``safety first'' approach.
    FAA response: This AD does not impose any requirements, including 
CAT I ILS, on non-U.S.-registered airplanes operating into the U.S. 
under part 129. Under ICAO Annex 8, Airworthiness of Aircraft, the 
state of registry of an airplane is the state responsible for its 
airworthiness. For this reason, FAA ADs apply only to U.S.-registered 
airplanes. To the extent the FAA's bilateral partners agree with the 
FAA's finding of an unsafe condition in U.S. airspace, the FAA 
encourages those authorities to adopt the FAA AD or similar 
requirements as mandatory continuing airworthiness instructions for 
airplanes registered in other countries. The FAA also plans to publish 
information in the FAA's Aeronautical Information Publication to alert 
international operators to the 5G C-Band situation in the U.S., 
including the agency's use of Domestic Notices. The FAA strongly urges 
operators of foreign-registered airplanes to voluntarily comply with 
the actions required by this AD when operating in the contiguous U.S. 
given the unsafe condition affects their airplanes as much as the 
airplanes subject to this AD.
3. Burden of Modification Requirement on Part 129 Operators
    Comment summary: IATA commented that the part 129 carriers are 
being disadvantaged by the proposed requirement to retrofit airplanes 
with an upgraded radio altimeter. Specifically, IATA stated that radio 
altimeter manufacturers are understandably prioritizing the equipment 
needs of the U.S. fleet over non-U.S. air carriers; IATA also referred 
to the FAA's exclusion of part 129 carriers from the roundtable 
discussions the FAA has held to consult with impacted carriers on the 
overall issue of 5G C-Band. Lufthansa Group, A4A, and ten other 
commenters (air carriers and trade associations) expressly agreed with 
IATA or stated similar concerns. Singapore Airways stated that the 
required modification will worsen the supply chain issue with upgraded 
radio altimeters.
    FAA response: Although supply chain disparities and issues are 
business matters beyond the authority of the FAA, the agency has worked 
with radio altimeter manufacturers and airplane operators to help 
ensure that filters and replacement units are available as quickly as 
possible. The FAA is aware of these issues and acknowledges the 
concerns regarding supply chain disruptions; however, due to the 
reliance on the radar altimeter inputs for low-visibility landings and 
the impending changes discussed in this final rule, the FAA has 
determined that the restrictions are necessary to correct the unsafe 
condition discussed in this AD.
    To the extent that the commenters expressed concern about the 
roundtable discussions, those discussions have been an overall 
collaboration among the many stakeholders affected by 5G C-Band 
deployment (U.S. federal agencies, the aerospace industry, the 
telecommunications companies, and foreign civil aviation authorities) 
and

[[Page 34072]]

have not been limited to the FAA's ADs. Participants in these 
discussions varied at each meeting; however, IATA was represented at 
some of the meetings.

N. Operator Involvement

    Comment summary: The Cargo Airlines Association commented that in 
addition to the airplane OEMs and radio altimeter manufacturers, 
airlines should participate in any future radio altimeter standards 
development activity.
    FAA response: Although airline operators are not usually members of 
a standards development activity, they have sometimes been members in 
the past for certain standards that have been airline operator centric. 
Individuals may apply for membership on a committee, and acceptance 
will be based on the committee chair's evaluation of the applicant.

O. PSD Curve and Associated Compliance Policy

1. Request for Part Numbers/Criteria for Radio Altimeter Tolerance
    Comment summary: Many commenters stated concern that the process 
for determining whether a radio altimeter meets the fundamental PSD 
curve, as specified in the proposed AD, is not well defined and that 
the requirement in the proposed AD of ``using a method approved by the 
FAA'' is not adequate. Thales requested that the FAA provide an Issue 
Paper, Advisory Circular, or other publicly available means of 
compliance document. Airbus requested that the FAA clarify where 
operators could find specific part numbers of radio altimeters that 
would meet the definition in the proposed AD. Fourteen commenters, as 
well as IATA and A4A, requested that the FAA provide a list of all 
radio altimeters by part number that are considered tolerant under the 
criteria discussed in the proposed AD. Gulf Air Group stated that 
developing an FAA-approved method to demonstrate that an airplane is 
radio altimeter tolerant should be the responsibility of the OEM, radio 
altimeter manufacturer, or system integrator.
    FAA response: The FAA has developed a policy statement that 
provides a means of compliance with this AD for all transport and 
commuter category airplanes and rotorcraft equipped with a radio 
altimeter. The FAA requested public comments on this proposed policy on 
May 8, 2023 [88 FR 29554]. The proposed policy describes an acceptable 
framework and method for demonstrating that an airplane or rotorcraft 
is radio altimeter tolerant. The policy discusses compliance methods 
that should be applied to programs for type certificates, amended type 
certificates, STCs, and amended STCs. Furthermore, the FAA does not 
maintain a list of tolerant radio altimeters because the determination 
of a radio altimeter tolerant airplane must consider the installation 
details, which vary from airplane to airplane. The proposed policy 
addresses how to assess 5G C-Band tolerance. Although most data 
submitted to demonstrate compliance in accordance with the FAA policy 
statement will be proposed by design approval holders, any person/
entity can propose a method to demonstrate compliance.
2. Request To Clarify Acceptability of External Filters
    Comment summary: Thales requested that the proposed AD be revised 
to clearly state that installations with external filters can also be 
used for compliance.
    FAA response: The FAA stated in the preamble of the NPRM that radio 
altimeter installations with external filters may be acceptable for 
compliance with the requirements of this AD. The FAA is not requiring a 
specific type of radio altimeter installation; the AD requires only 
that the radio altimeter installation meet the radio altimeter 
tolerance PSD curves. No change to this AD based is necessary based on 
this comment.
3. Request To Identify Spurious Emissions Data
    Comment summary: To determine what action may be necessary to 
ensure safe aviation operations in the U.S., Thales requested that the 
proposed AD include necessary spurious data that 5G network operators 
should disclose to the FAA.
    FAA response: The FAA disagrees. The spurious PSD curve that 
defines a radio altimeter tolerant airplane for purposes of this AD is 
based on the spurious emission limits documented in the voluntary 
agreement letter dated March 31, 2023.
4. Request To Clarify Figure 1
    Comment summary: Textron Aviation requested the FAA clarify at what 
reference point the PSD requirements apply. The commenter stated it 
assumed that they apply at the radio altimeter receive antenna input, 
such that antenna characteristics, coax loss, and filter 
characteristics would be included in the determination.
    FAA response: The FAA agrees and has changed the title of figure 1 
to paragraph (g)(1)(i) of this AD to reflect that the PSD requirements 
apply at the antenna input to the radio altimeter, and that the figure 
applies to the outward facing side of the antenna.
5. Request To Provide Additional Information on the Spurious Emission 
Tolerance
    Comment summary: AIA requested that the FAA provide more 
information about the tolerances for determination of whether an 
airplane is radio altimeter tolerant. Several commenters requested that 
the FAA add a new figure indicating the spurious tolerance, similar to 
the figure with the PSD tolerance curve, and a specification of the 
altitude dependence for spurious tolerance.
    FAA response: The FAA agrees and has replaced the proposed fixed 
emission level with a spurious PSD tolerance curve in figure 2 to 
paragraph (g)(1)(ii) of this AD. Subsequent figures have been 
redesignated accordingly.
6. Request To Recognize Installations as Minor Changes
    Comment summary: Two commenters requested that the FAA revise the 
proposed AD to allow modification of the airplane to a radio altimeter 
tolerant airplane as a minor change to type design, to help expedite 
approvals and make best use of resources.
    FAA response: The FAA disagrees. Under 14 CFR 21.95, minor design 
changes may be approved before an applicant submits to the FAA any 
substantiating data. Radio altimeters are critical sensors that must be 
shown to perform their intended function, and the modified hardware or 
software must be shown to still meet the airplane-level system safety 
requirements. For example, a filter may alter the radio altimeter 
performance, which may have an appreciable effect on reliability, 
operational characteristics, or other characteristics affecting 
airworthiness. For this reason, the FAA determined that FAA approval of 
the method used for the modification was necessary before operators 
could show compliance with this AD.
7. Request To Revise Tolerance Definition
    Comment summary: Textron and Embraer asked the FAA to add language 
to the definition of radio altimeter tolerant airplane to indicate the 
frequency band being referenced (3.7-3.98 GHz).
    FAA response: The FAA agrees and has changed paragraphs (g)(1)(i) 
and (ii) of this AD to include the applicable frequency bands.

[[Page 34073]]

8. Request To Add Certain PSD Limit
    Comment summary: Airbus and Bombardier requested that the FAA 
revise the table at the bottom of the proposed PSD curve to add the 
limit for 2500 feet above ground level. The commenters stated that this 
would be consistent with the maximum operating range of popular radio 
altimeter models installed on many airplanes and would avoid 
extrapolation errors.
    FAA response: The FAA disagrees. The FAA developed the PSD curve to 
cover all transport and commuter radio altimeters and has determined 
that any extrapolation errors are sufficiently small and will not 
affect compliance or compromise safety.
9. Request To Revise Tolerance Requirements for Certain Operations
    Comment summary: One commenter stated the proposed PSD values are 
not appropriate for some airplane operations. In support, the commenter 
stated that CAT I-only qualified airplanes do not require radio 
altimeter data, and that CAT II and CAT I qualified airplanes do not 
use radio altimeter data below 100 feet.
    FAA response: The FAA infers that the commenter is requesting that 
the proposed AD be revised for operators that perform only CAT I and 
CAT II approaches. The FAA disagrees. The unsafe condition identified 
by the FAA is related not only to low-visibility operations but also to 
the various flight deck effects such as erroneous Terrain Awareness and 
Warning System (TAWS) warnings, erroneous Traffic Collision Avoidance 
System (TCAS) warnings, erroneous landing gear warnings, and the 
erroneous display of radio altimeter data. Although these flight deck 
effects are less severe than the hazards associated with low-visibility 
landings, the FAA is concerned the effects will occur more frequently 
as 5G C-Band services continue to be deployed throughout the contiguous 
U.S. The erroneous warnings increase flightcrew workload as they try to 
ascertain the validity of the warning. Repeated determinations that the 
warning occurred in error will lead to flightcrew desensitization to 
warnings from these safety systems. Meeting the radio altimeter 
tolerant PSD curve will minimize erroneous flight deck warnings.
10. Request for Clarification of Spurious Emissions Limit
    Comment summary: MHI RJ stated that demonstrating tolerance to the 
aggregate base station conducted spurious emissions level is not 
possible at an airplane level since the received signal will depend on 
many other undefined factors, such as distance from base station and 
base station antenna performance. An individual commenter stated the 
spurious signal level of -48 dBm/MHz is not consistent with the FCC's 
regulator limit and free air attenuation, as the spurious signal and 
radio altimeter signals will attenuate as the airplanes gets farther 
from the 5G C-Band station.
    FAA response: As stated in section O.5. of this final rule, the FAA 
has determined that a spurious emissions PSD curve is a more 
appropriate method to define performance than a single aggregate 
spurious emissions level and revised this final rule accordingly.
11. Request for Different PSD Criteria
    Comment summary: An individual commenter stated the proposed AD 
would establish PSD criteria as though the 5G C-Band transmitter is 
located on the runway between threshold and touchdown zone, which is 
not realistic given the FAA approach criteria. The Department of 
Defense stated the PSD curve is lacking information to properly 
determine the impact to radio altimeters.
    FAA response: The FAA disagrees. The proposed PSD curve was 
validated using the actual locations of 5G C-Band transmitters with 
respect to runway safety zones at 5G CMAs.
12. Request To Revise Unit of Measurement
    Comment summary: AIA and ATR requested the FAA correct the 
references of dBm from ``decibels per megahertz'' to ``decibel-
milliwatts per megahertz.''
    FAA response: The FAA agrees; however, because the cited reference 
does not appear in this final rule, no change to the AD is necessary.
13. Request for AD Coverage of 65 dBm/MHz (Rural)
    Comment summary: Thales requested that the radio altimeter 
performance criteria specified in figure 1 to paragraph (g)(2) of the 
proposed AD be revised to explicitly cover any 5G emitter station up to 
65 dB/MHz in the applicable 3.7-3.98 GHz band.
    FAA response: The FAA performed additional analysis, considering 
both rural power levels (65 dBm/MHz) and urban power levels (62 dBm/
MHz), and determined that radio altimeter tolerant airplanes are safe 
to fly to all airports in the contiguous U.S. However, no change to the 
AD is necessary based on this comment.

P. RNP AR

1. Operation Under RNP AR IAP
    Comment summary: Some commenters expressed concern over the FAA's 
proposal to remove RNP AR IAPs from the list of prohibited operations. 
Allied Pilots Association and AIA stated RNP AR approaches are commonly 
used in high terrain environments where reliable TAWS functionality is 
necessary. ALPA requested information on maintaining operational safety 
while conducting RNP AR IAPs, especially at terrain-impacted runways.
    FAA response: The FAA included RNP AR in the original list of 
prohibited operations because it was unclear how 5G C-Band wireless 
broadband interference would affect this operation. Unlike other 
operations prohibited by the AD, RNP AR operations do not rely on 
direct radio altimeter inputs to determine arrival at minimums or for 
direct inputs that affect the flight path of the airplane. RNP AR 
operations require operational TAWS equipment; however, TAWS is not 
directly required for the procedure. An erroneous radio altimeter 
output could affect maximum allowed bank angle, which could affect 
course adherence. However, pilots would get an ``unable RNP'' message 
and take appropriate action. After further analysis, the FAA determined 
that 5G C-Band interference does not create an unsafe condition 
specific to the conduct of an RNP AR IAP. While there is a risk of 
erroneous TAWS warnings in the presence of 5G C-Band, that risk is not 
limited to RNP AR operations, but rather applies to all operations. To 
minimize the number of erroneous system messages and the unsafe 
condition they produce, the FAA is requiring that all airplanes 
operating under part 121 meet the PSD performance curves to operate in 
the contiguous U.S. after February 1, 2024.
2. Request To Clarify AFM Prohibitions
    Comment summary: Emirates stated that figure 3 to paragraph (i) and 
figure 4 to paragraph (j) of the proposed AD contain prohibitions for 
RNP AR IAPs and requested that the FAA clarify whether this is a 
typographical error.
    FAA response: In the NPRM, the FAA intentionally removed RNP AR 
from the proposed figures referenced by the commenter. This AD does not 
prohibit RNP AR IAPs.

Q. Additional Changes to NPRM

1. Request To Correct Paragraph Reference
    Comment summary: Qatar Airways suggested that the reference to

[[Page 34074]]

``paragraphs (k)(i) and (ii)'' in paragraph (k)(1) of the proposed AD 
be changed to ``paragraphs (k)(1)(i) and (ii).''
    FAA response: The commenter correctly noted this error in the 
proposed AD; however, because of other changes to paragraph (k)(1) of 
the proposed AD (paragraph (j) of this final rule), as described in 
section B.1. of this final rule, the requested change is not necessary.
2. Request To Remove Yabor[atilde] From Applicability
    Comment summary: An individual noted that the AD applicability 
includes Yabor[atilde] Ind[uacute]stria Aeron[aacute]utica S.A. 
(Yabor[atilde]), but the type certificate for Yabor[atilde] models is 
currently held by Embraer. The commenter suggested that Yabor[atilde] 
be removed from the applicability of this AD.
    FAA response: The FAA has removed Yabor[atilde] Ind[uacute]stria 
Aeron[aacute]utica S.A. from the applicability of this AD and corrected 
the clerical error by changing paragraph (c)(4) of this AD to state 
that type certificates previously held by Yabor[atilde] are now held by 
Embraer S.A. However, because paragraph (c) of this AD uses the 
language ``including, but not limited to,'' before listing the names of 
various type certificate holders, the AD applies to any transport or 
commuter category airplane equipped with a radio altimeter, regardless 
of the name of the type certificate holder. In this case, the AD 
applies to the airplanes whose type certificates were previously held 
by Yabor[atilde] that are now held by Embraer S.A.

R. Comments Outside Scope of NPRM

    Comment summary and FAA response: The FAA also received and 
reviewed several comments that were very general, stated the 
commenter's viewpoint without a suggestion specific to the AD, or did 
not make a request the FAA can act on. Some comments asked about other 
Boeing-specific ADs or about the updated radio altimeter MOPS. These 
comments are outside the scope of this AD.

Conclusion

    The FAA reviewed the relevant data, considered any comments 
received, and determined that air safety requires adopting this AD as 
proposed in the NPRM, except for the changes described previously. None 
of the changes will increase the economic burden on any operator. 
Accordingly, the FAA is issuing this AD to address the unsafe condition 
on these products.

Interim Action

    The FAA considers that this AD is an interim action. Once the TSO 
standard for radio altimeters is established, which will follow the 
existing international technical consensus on the establishment of the 
MOPS, the FAA anticipates that the MOPS will be incorporated into the 
TSO. Once a new radio altimeter TSO is developed, approved, and 
available, the FAA might consider additional rulemaking.

Effective Date

    Section 553(d) of the Administrative Procedure Act (APA) (5 U.S.C. 
551 et seq.) requires publication of a rule not less than 30 days 
before its effective date. However, section 553(d) authorizes agencies 
to make rules effective in less than 30 days when the agency finds 
``good cause.'' 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. Additionally, radio altimeter anomalies could lead to 
increased flightcrew workload and flightcrew desensitization to 
warnings. To address this unsafe condition, the actions required by 
this AD must be accomplished before the compliance date of June 30, 
2023. The FAA based this date on the changes to the 5G C-Band 
environment beginning on July 1, 2023. These changes include increased 
wireless broadband deployment and transmissions closer to the 
parameters authorized by the FCC. The earlier operators learn of the 
requirements in this AD, the earlier they can take action to ensure 
compliance. An effective date less than 30 days would ensure the AD is 
codified earlier, thereby increasing awareness of its requirements. 
Therefore, the FAA finds that good cause exists pursuant to 5 U.S.C. 
553(d) for making this amendment immediately effective.

Costs of Compliance

    The FAA estimates that this AD affects approximately 1,000 
airplanes of U.S. registry.
    As of the date of publication of this AD, there are approximately 
8,000 transport and commuter category airplanes of U.S. registry. In 
Special Airworthiness Information Bulletin AIR-21-18R2, the FAA 
requested radio altimeter retrofit plans, timelines, and completion 
information from the aviation industry. The FAA did not receive 
comprehensive data, but based on the limited information the agency did 
receive, the FAA extrapolated impacts across industry. Based on that 
information, the FAA roughly estimates that almost 7,000 airplanes on 
the U.S. registry have already been equipped or are being retrofitted 
to address radio altimeter interference tolerance, and thus will have 
to take no actions to comply with this AD. Based on information 
received, some operators will comply with the modification requirement 
by replacing the radio altimeter with a new upgraded or modified radio 
altimeter, and others will comply by installing an externally mounted 
filter. The FAA estimates that approximately 180 airplanes will require 
radio altimeter replacement and 820 airplanes will require addition of 
radio altimeter filters to comply with the modification requirement. As 
such, the FAA estimates the following costs to comply with this AD, for 
a total U.S. fleet cost of compliance of up to $35,152,000.

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                  Cost on U.S.
            Action                  Labor cost             Parts cost         Cost per product      operators
----------------------------------------------------------------------------------------------------------------
AFM revision until June 30,     1 work-hour x $85  $0.......................  $85.............  $85,000 for
 2023.                           per hour = $85.                                                 1,000 affected
                                                                                                 airplanes.
AFM revision after June 30,     1 work-hour x $85  $0.......................  $85.............  $85,000 for
 2023.                           per hour = $85.                                                 1,000 affected
                                                                                                 airplanes.
Modification (radio altimeter   .................  .........................  Up to $80,000     Up to
 replacement option).                                                          (includes parts   $14,400,000 for
                                                                               and labor).       180 affected
                                                                                                 airplanes.
Modification (filter addition   24 work-hours x    $8,000 per filter........  $10,040 per       Up to
 option).                        $85 per hour =                                filter.           $20,582,000 for
                                 $2,040 per                                                      820 affected
                                 filter.                                                         airplanes with
                                                                                                 2 or 3 filters
                                                                                                 per airplane.
----------------------------------------------------------------------------------------------------------------


[[Page 34075]]

    The benefits of the AD include the value of reducing aviation 
accident risks that are mitigated by TAWS, TCAS, and airborne windshear 
warning and flight guidance systems (windshear systems), all of which 
rely on proper performance of radio altimeters to perform their 
intended function. TAWS, TCAS, and windshear systems are examples of 
safety-enhancing systems required for operation under 14 CFR part 121. 
The FAA required these systems to address hazards that have caused 
accidents and fatalities during commercial air transportation in the 
U.S. This AD will maintain the same level of safety afforded by these 
and other safety systems before the use of the C-Band by 5G broadband 
networks. This AD will also minimize erroneous system messages and the 
unsafe condition they produce.

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 Flexibility Determination

    The Regulatory Flexibility Act (RFA) of 1980, Public Law 96-354, 94 
Stat. 1164 (5 U.S.C. 601-612), as amended by the Small Business 
Regulatory Enforcement Fairness Act of 1996 (Pub. L. 104-121, 110 Stat. 
857, Mar. 29, 1996) and the Small Business Jobs Act of 2010 (Pub. L. 
111-240, 124 Stat. 2504, Sept. 27, 2010), requires Federal agencies to 
consider the effects of the regulatory action on small business and 
other small entities and to minimize any significant economic impact.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    The FAA published an Initial Regulatory Flexibility Analysis (IRFA) 
(88 FR 1520, January 11, 2023) for Docket No. FAA-2022-1647, Project 
Identifier AD-2022-01379-T, to aid the public in commenting on the 
potential impacts to small entities. The FAA considered the public 
comments in developing both the final rule and this Final Regulatory 
Flexibility Analysis (FRFA). A FRFA must contain the following:
    (1) A statement of the need for, and objectives of, the rule;
    (2) A statement of the significant issues raised by the public 
comments in response to the IRFA, a statement of the assessment of the 
agency of such issues, and a statement of any changes made in the final 
rule as a result of such comments;
    (3) The response of the agency to any comments filed by the Chief 
Counsel for Advocacy of the SBA in response to the proposed rule, and a 
detailed statement of any change made in the final rule as a result of 
the comments;
    (4) A description of and an estimate of the number of small 
entities to which the rule will apply or an explanation of why no such 
estimate is available;
    (5) A description of the projected reporting, recordkeeping, and 
other compliance requirements of the proposed rule, including an 
estimate of the classes of small entities that will be subject to the 
requirement and the type of professional skills necessary for 
preparation of the report or record; and
    (6) A description of the steps the agency has taken to minimize the 
significant economic impact on small entities consistent with the 
stated objectives of applicable statutes, including a statement of the 
factual, policy, and legal reasons for selecting the alternative 
adopted in the final rule and why each of the other significant 
alternatives to the rule considered by the agency that affect the 
impact on small entities was rejected.

1. Need for and Objectives of the Rule

    This AD replaces AD 2021-23-12 and requires revising the 
limitations section of the existing AFM to incorporate limitations 
prohibiting certain operations requiring radio altimeter data for 
airplanes susceptible to 5G C-Band interference. This AD also requires 
modifying certain airplanes to allow safe operations in the U.S. 5G C-
Band radio frequency environment by February 1, 2024. The more 
restrictive limitations in this AD are needed due to the continued 
deployment of new 5G C-Band base stations whose signals are expected to 
cover most of the contiguous U.S. at transmission frequencies between 
3.7-3.98 GHz. This AD addresses the unsafe condition resulting from the 
continued deployment of 5G C-Band transmissions and their interference 
to radio altimeters.
    The FAA's legal basis for this AD is discussed in detail under the 
``Authority for this Rulemaking'' section.

2. Significant Issues Raised in Public Comments

    The FAA published an IRFA for Docket No. FAA-2022-1647, Project 
Identifier AD-2022-01379-T, and requested comments.
    One commenter stated that the vast majority of business airplane 
operators under part 91 are small businesses as defined by the SBA. The 
commenter requested that the FAA not underestimate the choice small 
businesses will have to make between an $80,000 retrofit and loss of 
utility of the airplane during adverse weather conditions.
    As explained in more detail in section 4. of this Regulatory 
Flexibility Determination, the FAA identified 31 small entities that 
own and operate airplanes affected by this AD. Those entities fall 
under North American Industry Classification System (NAICS) code 
481111, 481112, 481211, or 481212 with a small business size standard 
of a maximum of 1,500 employees, or under NAICS code 481219 with a 
small business size standard of a maximum of $25 million in average 
annual receipts, to be considered small business. The FAA did not 
receive any comments with data concerning this part of the FAA's 
regulatory analysis or concerning the estimated revenue impact for 
small businesses to comply with this AD. The FAA determined that no 
changes are necessary as a result of these comments.
    Lynden Air Cargo commented that there are significant costs 
associated with the research and development, approval, and type design 
amendment for new equipment. Textron commented that the costs 
associated with development and certification were not included in the 
FAA's cost estimate. Textron, Atlas Air, A4A, and Bombardier requested 
that the FAA include costs associated with impacts of the AD, such as 
delayed and canceled flights and the costs of restricted operations.
    The commenters are correct that these additional costs were not 
included in the FAA's estimated costs. The cost analysis in FAA AD 
rulemaking actions typically only contain the direct costs associated 
with the specific actions

[[Page 34076]]

required by the AD. The FAA does not include secondary costs such as 
the time necessary for planning or time necessitated by other 
administrative actions, or indirect costs such as those resulting from 
delayed or canceled flights and restricted operations. The FAA lacks 
the data necessary to quantify those costs, which might vary 
significantly among operators; the commenters did not provide such data 
either.
    Bombardier and an individual stated that the estimated cost of one 
work-hour per airplane at $85 per hour for revising an AFM was too low 
and omitted the costs of authoring the revisions, reviewing the 
revisions, and briefing flight crews.
    The FAA disagrees. The FAA uses one work-hour as a standard 
estimate in ADs that require an administrative function such as a 
revision to a flight manual. Operators and pilots must become familiar 
with the AFM before beginning a flight because of other FAA 
regulations, so that is not a cost associated with this AD.
    SkyWest Airlines commented that its part and labor costs for filter 
installation were nearly twice the costs specified in the NPRM and 
requested the FAA re-evaluate the cost estimate.
    The cost for filters specified in the NPRM was based on preliminary 
estimates. Based on this comment, the FAA has revised the cost estimate 
for the filter installation in this final rule.

3. Response to SBA Comments

    The Chief Counsel for Advocacy of the SBA did not file any comments 
in response to the NPRM.

4. Small Entities to Which the Rule Will Apply

    The FAA used the definition of small entities in the RFA for this 
analysis. The RFA defines small entities as small businesses, small 
governmental jurisdictions, or small organizations. In 5 U.S.C. 601(3), 
the RFA defines ``small business'' to have the same meaning as ``small 
business concern'' under section 3 of the Small Business Act. The Small 
Business Act authorizes the SBA to define ``small business'' by issuing 
regulations.
    SBA has established size standards for various types of economic 
activities, or industries, under the NAICS.\6\ These size standards 
generally define small businesses based on the number of employees or 
annual receipts.
---------------------------------------------------------------------------

    \6\ SBA Table of Size Standards. Effective March 17, 2023. 
https://www.sba.gov/document/support--table-size-standards.
---------------------------------------------------------------------------

    The following table shows the SBA size standards for FAA 
certificate holders. Note that the SBA definition of a small business 
applies to the parent company and all affiliates as a single entity.

            Small Business Size Standards: Air Transportation
------------------------------------------------------------------------
       NAICS code           Description           SBA size standard
------------------------------------------------------------------------
481111.................  Scheduled          1,500 employees.
                          Passenger Air
                          Transportation.
481112.................  Scheduled Freight  1,500 employees.
                          Air
                          Transportation.
481211.................  Nonscheduled       1,500 employees.
                          Chartered
                          Passenger Air
                          Transportation.
481212.................  Nonscheduled       1,500 employees.
                          Chartered
                          Freight Air
                          Transportation.
481219.................  Other              $25 million.
                          Nonscheduled Air
                          Transportation.
------------------------------------------------------------------------

    The modification costs of this AD affect certificate holders 
authorized to conduct operations under 14 CFR part 121. To identify 
which of those certificate holders may be small entities, the FAA 
reviewed readily available data sources (e.g., company websites) and 
data available to the FAA through its certificate oversight functions 
to determine whether the certificate holder meets the applicable size 
standard. The following table provides a summary of the estimated 
number of small entities to which this AD applies.

                                       Estimated Number of Small Entities
----------------------------------------------------------------------------------------------------------------
                                                                  Number of     Number small      Percent small
                            Category                               entities       entities          entities
----------------------------------------------------------------------------------------------------------------
Major..........................................................            6                 0                 0
National.......................................................           15                 7                47
Passenger and Cargo Charter....................................           12                 8                67
Regional.......................................................           15                 7                47
Specialty Cargo................................................           14                 9                64
                                                                ------------------------------------------------
    Total......................................................           62                31                50
----------------------------------------------------------------------------------------------------------------

    Therefore, the FAA estimated that this AD impacts 31 small 
entities.

5. Projected Reporting, Recordkeeping, and Other Compliance 
Requirements

    No new recordkeeping or reporting requirements are associated with 
the AD. As discussed previously, the FAA estimates that the majority of 
airplanes operated by small entities will already be equipped in a 
manner that requires no actions to comply with this AD. For the 
remaining number of airplanes, small entity compliance with the AD 
would entail incorporation of AFM revisions at an approximate cost of 
$170 per airplane. For the modification requirement of this AD, the FAA 
anticipates that a small number of airplanes will need to have radio 
altimeter filters installed (at an approximate cost of $10,040 per 
filter), and a smaller number of airplanes will require a radio 
altimeter replacement (at an approximate cost of up to $80,000 per 
airplane). These costs represent a small percentage of the overall cost 
of owning and operating a transport category airplane. To the extent 
that small entities provide more unique services or serve markets with 
less

[[Page 34077]]

competition, these entities might be able to pass on these compliance 
costs to their customers in the form of price increases.

6. Significant Alternatives Considered

    As part of the FRFA, the FAA is required to consider regulatory 
alternatives that may be less burdensome. The FAA did not find any 
significant regulatory alternatives that would still accomplish the 
safety objectives of this AD.
    Operators may also propose a less burdensome method for mitigating 
the unsafe condition using the AMOC procedures found in 14 CFR 39.19.

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.
    For the reasons discussed above, I certify that this AD:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866, and
    (2) Will not affect intrastate aviation in Alaska.

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:
0
a. Removing Airworthiness Directive (AD) 2021-23-12, Amendment 39-21810 
(86 FR 69984, December 9, 2021); and
0
b. Adding the following new AD:

2023-10-02 Transport and Commuter Category Airplanes: Amendment 39-
22438; Docket No. FAA-2022-1647; Project Identifier AD-2022-01379-T.

(a) Effective Date

    This airworthiness directive (AD) is effective May 26, 2023.

(b) Affected ADs

    This AD replaces AD 2021-23-12, Amendment 39-21810 (86 FR 69984, 
December 9, 2021) (AD 2021-23-12).

(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 
(18) of this AD.
    (1) The Boeing Company
    (2) Airbus SAS
    (3) Bombardier Inc.
    (4) Embraer S.A. (including type certificates previously held by 
Yabor[atilde] Ind[uacute]stria Aeron[aacute]utica S.A., which are 
now held by 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) MHI RJ Aviation ULC
    (15) BAE Systems (Operations) Limited
    (16) Lockheed Martin Corporation/Lockheed Martin Aeronautics 
Company
    (17) Viking Air Limited
    (18) 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 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. 
Additionally, radio altimeter anomalies could lead to increased 
flightcrew workload and flightcrew desensitization to warnings.

(f) Compliance

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

(g) Definitions

    (1) For purposes of this AD, a ``radio altimeter tolerant 
airplane'' is one for which the radio altimeter, as installed, 
demonstrates the tolerances specified in paragraphs (g)(1)(i) and 
(ii) of this AD, using a method approved by the FAA. No actions are 
required by this AD for radio altimeter tolerant airplanes.
    (i) Tolerance to radio altimeter interference, for the 
fundamental emissions (3.7-3.98 GHz), at or above the power spectral 
density (PSD) curve threshold specified in figure 1 to paragraph 
(g)(1)(i) of this AD.

Figure 1 to paragraph (g)(1)(i)--Fundamental Effective Isotropic PSD 
at Outside Interface of Airplane Antenna
BILLING CODE 6820-61-P

[[Page 34078]]

[GRAPHIC] [TIFF OMITTED] TR26MY23.030

    (ii) Tolerance to radio altimeter interference, for the spurious 
emissions (4.2-4.4 GHz), at or above the PSD curve threshold 
specified in figure 2 to paragraph (g)(1)(ii) of this AD.

Figure 2 to paragraph (g)(1)(ii)--Spurious Effective Isotropic PSD 
at Outside Interface of Airplane Antenna

[[Page 34079]]

[GRAPHIC] [TIFF OMITTED] TR26MY23.031

    (2) For purposes of this AD, a ``non-radio altimeter tolerant 
airplane'' is one for which the radio altimeter, as installed, does 
not demonstrate the tolerances specified in paragraphs (g)(1)(i) and 
(ii) of this AD.

(h) Airplane Flight Manual (AFM) Revision Until June 30, 2023

    For non-radio altimeter tolerant airplanes, before further 
flight, revise the Limitations Section of the existing AFM to 
include the information specified in figure 3 to paragraph (h) of 
this AD. This may be done by inserting a copy of figure 3 to 
paragraph (h) of this AD into the existing AFM. If an operator has 
complied with paragraph (g) of AD 2021-23-12, that action satisfies 
the requirements of this paragraph.

Figure 3 to paragraph (h)--AFM Revision

[[Page 34080]]

[GRAPHIC] [TIFF OMITTED] TR26MY23.032

(i) AFM Revision After June 30, 2023

    For non-radio altimeter tolerant airplanes, do the actions 
specified in paragraphs (i)(1) and (2) of this AD.
    (1) On or before June 30, 2023, revise the Limitations Section 
of the existing AFM to include the information specified in figure 4 
to paragraph (i) of this AD. This may be done by inserting a copy of 
figure 4 to paragraph (i) of this AD into the existing AFM. 
Incorporating the AFM revision required by this paragraph terminates 
the AFM revision required by paragraph (h) of this AD.
    (2) Before further flight after incorporating the limitations 
specified in figure 4 to paragraph (i) of this AD, remove the AFM 
revision required by paragraph (h) of this AD.

Figure 4 to paragraph (i)--AFM Revision for Non-Radio Altimeter 
Tolerant Airplanes
[GRAPHIC] [TIFF OMITTED] TR26MY23.033

(j) Terminating Action for AFM Limitations

    (1) Modifying the airplane from a non-radio altimeter tolerant 
airplane to a radio altimeter tolerant airplane terminates the 
limitations in paragraph (i) of this AD for that airplane.
    (2) After modifying the airplane to a radio altimeter tolerant 
airplane, the limitations specified by paragraph (i) of this AD may 
be removed from the AFM.

(k) 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 (l) 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.
    (3) AMOCs approved for AD 2021-23-12 are approved as AMOCs for 
the requirements specified in paragraph (h) of this AD.

(l) 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].

(m) Material Incorporated by Reference

    None.


[[Page 34081]]


    Issued on May 23, 2023.
Michael Linegang,
Acting Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-11371 Filed 5-24-23; 11:15 am]
BILLING CODE 4910-13-C