[Federal Register Volume 88, Number 88 (Monday, May 8, 2023)]
[Proposed Rules]
[Pages 29554-29555]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-09622]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 88, No. 88 / Monday, May 8, 2023 / Proposed 
Rules  

[[Page 29554]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 21

[Docket No. FAA-2023-0938]


Proposed Policy Statement; Demonstration of Radio Altimeter 
Tolerant Aircraft

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notification of availability; request for comments.

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SUMMARY: This document announces the availability of a draft Policy 
Statement PS-AIR-600-39-01, Demonstration of Radio Altimeter Tolerant 
Aircraft. The FAA invites public comment on PS-AIR-600-39-01.

DATES: The FAA must receive comments on this document on or before June 
7, 2023.

ADDRESSES: You may send comments identified by docket number FAA-2023-
0938 using any of the following methods:
    [squ] Federal eRulemaking Portal: Go to www.regulations.gov and 
follow the instructions for submitting comments electronically.
    [squ] Mail: U.S. Department of Transportation, Docket Operations, 
M-30, 1200 New Jersey Avenue SE, Room W12-140, West Building Ground 
Floor, Washington, DC 20590-0001.
    [squ] Hand Delivery: Deliver to Mail address above between 9 a.m. 
and 5 p.m., Monday through Friday, except Federal holidays.
    [squ] Fax: (202) 493-2251.
    Docket: Background documents or comments received may be read at 
www.regulations.gov at any time. Follow the online instructions for 
accessing the docket or go to the Docket Operations in Room W12-140 of 
the West Building Ground Floor at 1200 New Jersey Avenue SE, 
Washington, DC, between 9 a.m., and 5 p.m., Monday through Friday, 
except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Barbara Clark, Aviation Safety 
Specialist, Avionics and Electrical Systems Section, 800 Independence 
Ave. SW, DC 20591; telephone: 817-222-5390; email: 
[email protected].

SUPPLEMENTARY INFORMATION: 
    Privacy: The FAA will post all comments it receives, without 
change, to www.regulations.gov, including any personal information the 
commenter provides. Using the search function of the docket website, 
anyone can find and read the electronic form of all comments received 
into any FAA docket, including the name of the individual sending the 
comment (or signing the comment for an association, business, labor 
union, etc.). DOT's complete Privacy Act Statement can be found in the 
Federal Register published on April 11, 2000 (65 FR 19477-19478), as 
well as at https://DocketsInfo.dot.gov.

Comments Invited

    The FAA invites interested parties to take part in the development 
of the proposed policy statement by sending written comments to an 
address listed under ADDRESSES. Include Docket No. FAA-2023-0938; 
Policy No. PS-AIR-600-39-01 at the beginning of your comments. The most 
helpful comments reference a specific portion of the proposal, explain 
the reason for any recommended change, and include supporting data. The 
FAA will consider all comments received by the closing date and may 
amend the proposal because of those comments.
    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in 14 CFR 
11.35, the FAA will post all comments received, without change, to 
regulations.gov, including any personal information you provide. The 
agency will also post a report summarizing each substantive verbal 
contact received about this proposed policy.

Confidential Business Information

    CBI is commercial or financial information that is both customarily 
and actually treated as private by its owner. Under the Freedom of 
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public 
disclosure. If your comments responsive to this notice contain 
commercial or financial information that is customarily treated as 
private, that you actually treat as private, and that is relevant or 
responsive to this notice, it is important that you clearly designate 
the submitted comments as CBI. Please mark each page of your submission 
containing CBI as ``PROPIN.'' The FAA will treat such marked 
submissions as confidential under the FOIA, and they will not be placed 
in the public docket of this notice. Submissions containing CBI should 
be sent to the individual listed under FOR FURTHER INFORMATION CONTACT. 
Any commentary that the FAA receives that is not specifically 
designated as CBI will be placed in the public docket for this notice.

Background

    The current performance standards for radio altimeters (also known 
as radar altimeters) are based on the presumption that no occupancy of 
an adjacent radio frequency spectrum would cause interference with 
radio altimeters. During 2021, the radio frequency operating 
environment surrounding radio altimeters substantially changed when 
wireless telecommunication service providers began offering 5G C-Band 
services near the 4.2-4.4 GHz band, which is reserved for aviation 
radio altimeters. The FAA subsequently determined that radio altimeters 
cannot be relied upon to perform their intended function if they 
experience interference from 5G wireless broadband operations in the C-
Band.
    Deployment of the new 5G C-Band services prompted the FAA to 
address the risks posed by radio frequency (RF) interference to radio 
altimeters. On December 7, 2021, the FAA issued AD 2021-23-12 \1\ for 
transport and commuter category airplanes equipped with a radio 
altimeter and AD 2021-23-13 \2\ for helicopters equipped with a radio 
altimeter. AD 2021-23-12 and AD 2021-23-12 prohibit certain flight 
operations requiring radio altimeter data when flying in the presence 
of 5G C-Band interference as identified by Notices to Air Missions 
(NOTAMs). In response to AD 2021-23-12, the aviation industry developed 
a method to show compatibility with 5G emissions

[[Page 29555]]

in the United States national airspace system for the initial 5G 
deployment, which was limited to 3.7-3.8 GHz, and the 5G spurious 
emissions in the radio altimeter band (4.2-4.4 GHz). The FAA accepted 
this method as support for proposals for alternative methods of 
compliance (AMOCs) with AD 2021-23-12 and AD 2021-23-13. These AMOCs 
used standardized assessment parameters, values, and methods to 
estimate an installed altimeter system protection radii or distance. 
Aircraft with an altimeter operating beyond this distance from all 5G 
base stations would not expect deleterious effects from RF 
incompatibility and indeed could depend upon the radio altimeter system 
to fully perform its intended function. These AMOCs were based on 
interference thresholds of specific individual radio altimeter 
transceivers. That is, each transceiver was tested to benchmark their 
performance in the presence of out-of-band and in-band C-Band signals. 
The thresholds were then modified and tailored to installation factors 
specific to the installed platform (e.g., measured antenna gains and 
line losses). These values were then used to determine the necessary 
mitigations to protect the airport airspace most critical for the 
safety of operations. The mitigations included actions by wireless 
providers as well as flight limitations imposed by the FAA for the 
airspace areas identified by NOTAM, unless operating under an approved 
AMOC.
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    \1\ Amendment 39-21810, 86 FR 69984, December 9, 2021.
    \2\ Amendment 39-21811, 86 FR 69992, December 9, 2021.
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    On January 6, 2023, the FAA issued a notice of proposed rulemaking 
(NPRM) proposing to supersede AD 2021-23-12.\3\ On April 5, 2023, the 
FAA issued an NPRM proposing to supersede AD 2021-23-13.\4\ The flight 
limitations in the new proposed ADs would depend on whether an aircraft 
has a radio altimeter that demonstrates certain tolerances using a 
method approved by the FAA.
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    \3\ Docket No. FAA-2022-1647, 88 FR 1520 (January 11, 2023).
    \4\ Docket No. FAA-2023-0668, 88 FR 21931 (April 12, 2023).
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Proposed Policy Statement

    This proposed policy would provide guidance for operators and 
manufacturers to demonstrate an aircraft is a radio altimeter tolerant 
aircraft, under the proposed definition in the NPRMs.
    You may review the proposed policy statement at www.regulations.gov 
in Docket No. FAA-2023-0938; or on the FAA's website at www.faa.gov/aircraft/draft_docs/.

    Issued on May 2, 2023.
Michael Linegang,
Acting Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-09622 Filed 5-5-23; 8:45 am]
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