Rule2023-14927
Demonstration of Radio Altimeter Tolerant Aircraft
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
July 19, 2023
Effective
July 19, 2023
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
The Federal Aviation Administration (FAA) announces Policy Statement PS-AIR-600-39-01 for demonstrating an aircraft is a "radio altimeter tolerant airplane" or a "radio altimeter tolerant rotorcraft" using a method approved by the FAA.
Full Text
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<title>Federal Register, Volume 88 Issue 137 (Wednesday, July 19, 2023)</title>
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[Federal Register Volume 88, Number 137 (Wednesday, July 19, 2023)]
[Rules and Regulations]
[Pages 46055-46057]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-14927]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 21
[Docket No. FAA-2023-0938]
Demonstration of Radio Altimeter Tolerant Aircraft
AGENCY: Federal Aviation Administration, DOT
ACTION: Notice of availability; final policy and disposition of
comments.
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SUMMARY: The Federal Aviation Administration (FAA) announces Policy
Statement PS-AIR-600-39-01 for demonstrating an aircraft is a ``radio
altimeter tolerant airplane'' or a ``radio altimeter tolerant
rotorcraft'' using a method approved by the FAA.
DATES: This policy is effective July 19, 2023.
FOR FURTHER INFORMATION CONTACT: For technical questions concerning
this policy statement, contact Barbara Clark, Supervisory Aviation
Safety Specialist, Avionics Navigation & Flight Deck Unit (AIR-626B),
800 Independence Ave. SW, Washington, DC 20591; telephone: 202-267-
8569; email: <a href="/cdn-cgi/l/email-protection#ef8d8e9d8d8e9d8ec18c838e9d84af898e8ec1888099"><span class="__cf_email__" data-cfemail="94f6f5e6f6f5e6f5baf7f8f5e6ffd4f2f5f5baf3fbe2">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
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 (RF) 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. In both the U.S. and
internationally, this band is allocated on a primary basis for
aeronautical radionavigation service, which is used by aviation radio
altimeters. The FAA subsequently determined that radio altimeters could
not 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 RF interference to radio altimeters. On
December 7, 2021, the FAA issued airworthiness directive (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 2021-23-13 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 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 harmful effects from RF incompatibility and indeed
could depend upon the radio altimeter system to perform fully 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.\3\ The thresholds were then
modified and tailored to installation factors specific to the installed
platform (e.g., measured antenna gains and cable 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.
\3\ ``In-band signals'' have frequencies in the radio altimeter
band of 4.2-4.4 GHz. The frequencies of ``out-of-band'' signals are
outside of the radio altimeter band.
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The deployment of new 5G C-Band stations continues. Their signals
are expected to cover most of the contiguous United States at
transmission frequencies between 3.7-3.98 GHz.\4\
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\4\ Federal Communications Commission (FCC) Report and Order 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, see
<a href="https://www.fcc.gov">https://www.fcc.gov</a>.
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On May 26, 2023, the FAA superseded AD 2021-23-12 with AD 2023-10-
02.\5\ The flight limitations imposed by AD 2023-10-02 depend on
whether an airplane has a radio altimeter system that demonstrates the
tolerances specified in paragraph (g)(1) of the AD using a method
approved by the FAA (i.e., whether the aircraft is a ``radio altimeter
tolerant airplane'').\6\
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\5\ Amendment 39-22438, 88 FR 34065, May 26, 2023.
\6\ The FAA subsequently issued several ADs to address 5G
interference for specific Boeing airplane models: AD 2023-12-05, AD
2023-12-10, AD 2023-12-11, AD 2023-12-12, AD 2023-12-13, AD 2023-12-
14, and AD 2023-12-15.
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On June 22, 2023, the FAA superseded AD 2021-23-13 with AD 2023-11-
07.\7\ The flight limitations imposed by AD 2023-11-07 depend on
whether a rotorcraft has a radio altimeter system that demonstrates the
tolerances specified in paragraph (g)(1) of the AD using a method
approved by the FAA (i.e., whether the aircraft is a ``radio altimeter
tolerant rotorcraft'').
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\7\ Amendment 39-22453, 88 FR 40685, June 22, 2023.
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The FAA published a notice of availability and request for comments
on proposed guidance for demonstrating an aircraft is a ``radio
altimeter tolerant aircraft'' in the Federal Register on May 8, 2023
(88 FR 29554). The public comment period for the notice closed on June
7, 2023.
[[Page 46056]]
Discussion of Comments
The FAA received comments from eight organizations: Thales Group,
Airlines for America (A4A), MHI RJ Aviation ULC, Dassault Aviation
(Dassault), Embraer S.A. (Embraer), the Cargo Airline Association
(CAA), Gulfstream Aerospace Corporation (Gulfstream), and the Aviation
Coalition. Comments fell into broad categories to include requests
regarding how to show compliance; suggestions to harmonize language
between the policy and the newly published ADs; statements regarding 5G
bandwidth, and recommendations on content, editing, and formatting. One
commenter urged the FAA to withdraw the policy.
A copy of the FAA's disposition of the public comments received is
also available at <a href="http://regulations.gov">regulations.gov</a> in Docket No. FAA-2023-0938.
A. Showing Compliance
The FAA received several comments regarding how to show compliance
with the policy statement and with AD 2023-10-02 or AD 2023-11-07.
Thales Group asked if performance justifications submitted for a
prior AD must be re-submitted as evidence to support compliance with AD
2023-10-02 or AD 2023-11-07. Performance justification evidence must be
re-submitted to the FAA to show compliance. Performance justifications
for prior ADs were approved by the FAA before the method in the policy
statement was defined. Although the FAA expects that aircraft with
AMOCs approved for prior ADs may be able to meet the definition of a
``radio altimeter tolerant airplane'' or ``radio altimeter tolerant
rotorcraft,'' design approval holders (DAHs) or operators will need to
provide the FAA with data showing explicitly that the aircraft meets
the tolerances in paragraph (g)(1) of AD 2023-10-02 or AD 2023-11-07
before the FAA will approve the method they propose to use. However,
the FAA has updated the policy statement to clarify that data
previously submitted for AMOCs with AD 2021-23-12 or AD 2021-23-13 may
be referenced to support the method in PS-AIR-600-39-01 without re-
submitting the referenced documents themselves.
Gulfstream commented that the policy allows for the use of existing
data and analysis, which manufacturers collected for AMOCs with AD
2021-23-12 or AD 2021-23-13, to demonstrate compliance with the new AD.
The FAA acknowledges that while the use of existing data is supported,
additional data and analysis is not precluded. The use of power
spectral density (PSD) curves for compliance demonstration is
different.
Gulfstream and CAA requested that the FAA identify the radio
altimeter technologies that meet the AD requirements. Gulfstream stated
the policy creates a duplicative effort and burden on the aviation
community in that it asks for data the FAA already possesses based on
prior AMOC approvals. CAA stated that the policy creates an undue
burden on operators to coordinate with DAHs and radio altimeter
manufacturers.
The FAA disagrees. The FAA approved AMOCs for AD 2021-23-12 and AD
2021-23-13 before the radio altimeter tolerant PSD curves were defined.
Although the FAA expects that the aircraft with AMOCs approved for AD
2021-23-12 or AD 2021-23-13 may be able to meet the definition of
``radio altimeter tolerant'' aircraft, DAHs will need to provide the
FAA with data showing explicitly that the aircraft meets the tolerances
in AD 2023-10-02 or AD 2023-11-07 before the FAA will approve the
method they propose to use. Additionally, the FAA does not maintain a
list of tolerant radio altimeters; the determination of a radio
altimeter tolerant aircraft must consider the installation details,
which vary from aircraft to aircraft. However, the FAA has added
guidance to the policy to assist with obtaining FAA approval
expeditiously.
CAA requested the FAA accept requests for AMOCs for operators to
continue to operate without restrictions after July 1, 2023, given the
same level of safety could be achieved. Operators will not need an AMOC
provided their aircraft meets the fundamental and spurious emissions
PSD curve thresholds specified in AD 2023-10-02 and AD 2023-11-07. No
flight restrictions are mandated by AD 2023-10-02 and AD 2023-11-07 for
radio altimeter tolerant aircraft.
Dassault requested the FAA confirm whether bench tests performed by
the transceiver manufacturer would be sufficient for substantiation
without additional tests. The FAA partially agrees. Bench tests of
multiple units of a given transceiver model; antenna patterns, both in-
band and out-of-band; and an analysis of the installed system to
determine the appropriate cable loss are all necessary for
substantiation. A test of the system (transceiver, antenna(s), and
cabling) when installed on the aircraft is not necessary.
B. Harmonize Guidance
The guidance for spurious emissions in the proposed policy
statement was based on a spurious emission level. When the FAA issued
AD 2023-10-02 and AD 2023-11-07, the FAA replaced the proposed fixed
emission level with a spurious PSD tolerance curve.
Embraer, Dassault, and the Aviation Coalition requested the FAA
revise numerous references in the policy from the spurious level to the
spurious emissions PSD curve to be consistent with AD 2023-10-02 and AD
2023-22-07. The FAA agrees and has revised the policy statement
accordingly.
C. 5G Bandwidth and Interference
The Aviation Coalition requested the FAA clarify whether actual 5G
C-band transmissions will present a condition where cumulative 5G
signaling bandwidths in excess of 100 MHz will be in practice after
July 1, 2023. It commented that the cumulative impact of multiple 100
MHz bands is not fully characterized for existing altimeters. The
Aviation Coalition further stated the current accepted practice
reflects the use of 100 MHz 5G signaling bandwidth for the purposes of
compatibility assessment between 5G and radio altimeters. The FAA does
not expect cumulative 5G signaling bandwidths in excess of 100 MHz for
a given frequency at any one location in practice, based on
communication with the FCC.
The Aviation Coalition asked why the policy specifies an
interference tolerance threshold (ITT) measurement since the
superseding ADs establish a curve for fundamental tolerance thresholds.
The commenter stated it should be sufficient for an applicant to test
to the appropriate tolerance levels of the curve and show that the
radio altimeter performance at those levels is not unacceptably
degraded. The FAA agrees that compliance with the curve can be
determined without necessarily determining the transceiver's
performance limit. The FAA changed the policy to reflect an
interference tolerance (IT) measurement instead of an ITT measurement
and updated the definition accordingly.
Dassault requested the FAA add the exact 5G fundamental frequency
bandwidth to the guidance. The FAA agrees and has revised the document
accordingly.
D. Definitions, Editing, and Formatting
The FAA agreed with multiple requests from Dassault and the
Aviation Coalition for editorial and formatting changes and
reorganization, and revised the proposed policy statement accordingly,
including the following:
<bullet> The FAA added introductory text to the beginning of sections 1
and 2.
[[Page 46057]]
<bullet> The FAA added a diagram as figure 1 for clarity and improve
understanding.
<bullet> The FAA added a definition of the ``stair-step method'' to
sections 1 and 2.
<bullet> The FAA changed ``the log-linear interpolation'' to ``a log-
linear interpolation,'' as both terms are equivalent.
<bullet> The FAA changed ``line losses'' to ``cable losses'' for
consistency in terminology.
<bullet> The FAA moved the discussion of the 5G spurious PSD formula
from paragraph 2.c to the introductory part of section 2.
Dassault asked whether the performance criteria in the policy
section only applies to the transceiver. The performance criteria
applies to the installed radio altimeter system. The FAA notes that the
equations include terms to characterize the performance of the entire
system. The FAA has replaced four instances of ``radio altimeter'' with
``radio altimeter system'' to clarify.
The FAA disagreed with the Aviation Coalition's request to revise
the language in paragraph 2.a regarding base stations. The statement is
correct as written, as it is a factual definition of 5G base station
and aircraft compatibility. For clarity, the FAA moved the statement to
the policy section before section 1 as background information.
E. Request for the FAA To Withdraw the Policy
A4A requested the FAA withdraw the proposed policy because
operators who are not DAHs do not have the data and information to show
compliance with the methods in the policy without significant
assistance from aircraft original equipment manufacturers (OEMs) and
radio altimeter manufacturers. A4A stated this would be infeasible
given the short compliance timeframe, as well as duplicative since the
same data and information associated with aircraft type and radio
altimeter technology combination will have already been submitted to
the FAA by the DAH/OEM. Lastly, A4A stated the FAA does not have the
appropriate resources to timely coordinate and evaluate every
operator's submissions while simultaneously reviewing data submitted by
the DAH/OEM. Alternatively, A4A requested that operators who are not
DAHs be permitted to submit a letter of compliance to their principal
avionics inspector, citing either an FAA-published list of compliant
aircraft model/radio altimeter combinations or a list from the DAH/OEM.
The FAA disagrees with withdrawing the policy, as it provides
guidance for obtaining FAA approval of a method showing compliance with
AD 2023-10-02 and AD 2023-11-07. However, the FAA has added guidance to
the policy to assist with obtaining FAA approval expeditiously.
F. Request Regarding Horizontal Separation for Rotorcraft
The Aviation Coalition noted that language in the proposed policy
referring to horizontal separation distance by wing span may be
appropriate for airplanes, but not for rotorcraft. Because of other
changes made to the policy statement (replacing the proposed spurious
emissions level with a spurious PSD curve), the language noted by the
commenter has been removed from the document. As a result, no change to
the policy is necessary.
G. Request To Include ``Should''
The Aviation Coalition requested that the FAA add the word
``should'' to several places throughout the policy statement, to be
consistent with nature of the policy as a guidance document. The FAA
disagrees as the specified language identifies how to use the guidance
in this policy as a means of compliance. In some instances, the
language specified by the commenter defines a certain value and
therefore the addition of ``should'' would be inappropriate.
H. Request To Clarify
MHI RJ Aviation ULC requested the FAA clarify an apparent
inconsistency between figure 1 in AD 2023-10-02 and AD 2023-11-07 and
the section of the policy on 5G spurious tolerance. The FAA understands
the commenter to be comparing the fundamental PSD curve in AD 2023-10-
02 with guidance for spurious tolerance in the policy statement.
Policy
The FAA's policy statement provides guidance for operators and
manufacturers to demonstrate an aircraft is a radio altimeter tolerant
aircraft, as defined in AD 2023-10-02 and AD 2023-11-07.You may view
the final policy statement, PS-AIR-600-39-01, Demonstration of Radio
Altimeter Tolerant Aircraft, at <a href="http://regulations.gov">regulations.gov</a> in Docket No. FAA-2023-
0938 or on the FAA's Dynamic Regulatory System website at <a href="http://drs.faa.gov">drs.faa.gov</a>.
Issued in Des Moines, Washington on July 10, 2023.
Suzanne A. Masterson,
Acting Manager, Technical Innovation Policy Branch, Policy and
Innovation Division, Aircraft Certification Service.
[FR Doc. 2023-14927 Filed 7-18-23; 8:45 am]
BILLING CODE 4910-13-P
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</html>Indexed from Federal Register on July 19, 2023.
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