Airworthiness Directives; Various Helicopters

Issuing agencies

Abstract

The FAA proposes to adopt a new airworthiness directive (AD) for all helicopters equipped with a radio (also known as radar) altimeter. This proposed AD was prompted by the 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 to 3.98 GHz frequency band (5G Lower C-Band) while operating in Canadian airspace. This proposed AD would require revising the existing rotorcraft flight manual (RFM) for the helicopter to incorporate limitations prohibiting certain operations requiring radio altimeter data when operating within Canadian airspace. The FAA is proposing this AD to address the unsafe condition on these products.

Full Text

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<title>Federal Register, Volume 91 Issue 194 (Thursday, October 8, 2026)</title>
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[Federal Register Volume 91, Number 194 (Thursday, October 8, 2026)]
[Proposed Rules]
[Pages 64309-64315]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-20677]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2026-11799; Project Identifier MCAI-2026-00594-R]
RIN 2120-AA64


Airworthiness Directives; Various Helicopters

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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[[Page 64310]]

SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for all helicopters equipped with a radio (also known as radar) 
altimeter. This proposed AD was prompted by the 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 to 3.98 GHz frequency band (5G Lower C-Band) 
while operating in Canadian airspace. This proposed AD would require 
revising the existing rotorcraft flight manual (RFM) for the helicopter 
to incorporate limitations prohibiting certain operations requiring 
radio altimeter data when operating within Canadian airspace. The FAA 
is proposing this AD to address the unsafe condition on these products.

DATES: The FAA must receive comments on this proposed AD by November 
23, 2026.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
    <bullet> Federal eRulemaking Portal: Go to <a href="http://regulations.gov">regulations.gov</a>. Follow 
the instructions for submitting comments.
    <bullet> Fax: 202-493-2251.
    <bullet> Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE, Washington, DC 20590.
    <bullet> Hand Delivery: Deliver to Mail address above between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    AD Docket: You may examine the AD docket at <a href="http://regulations.gov">regulations.gov</a> under 
Docket No. FAA-2026-11799; 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 NPRM, the mandatory continuing airworthiness 
information (MCAI), any comments received, and other information. The 
street address for Docket Operations is listed above.

FOR FURTHER INFORMATION CONTACT: Ken Fairhurst, Continued Operational 
Safety Technical Advisor, FAA, 2200 South 216th St., Des Moines, WA 
98198; phone: 817-222-5390; email: <a href="/cdn-cgi/l/email-protection#a8c7d8cddac9dcc1c7c6c9c4dbc9cecddcd1e8cec9c986cfc7de"><span class="__cf_email__" data-cfemail="2d425d485f4c594442434c415e4c4b4859546d4b4c4c034a425b">[email&#160;protected]</span></a>.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites you to send any written relevant data, views, or 
arguments about this proposal. Send your comments using a method listed 
under the ADDRESSES section. Include ``Docket No. FAA-2026-11799; 
Project Identifier MCAI-2026-00594-R'' 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 
<a href="http://regulations.gov">regulations.gov</a>, including any personal information you provide. The 
agency will also post a report summarizing each substantive verbal 
contact received about this NPRM.

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 NPRM 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 NPRM, 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 NPRM. Submissions containing CBI should be sent to Ken 
Fairhurst, Continued Operational Safety Technical Advisor, FAA, 2200 
South 216th St., Des Moines, WA 98198; phone: 817-222-5390; email: 
<a href="/cdn-cgi/l/email-protection#402f3025322134292f2e212c332126253439002621216e272f36"><span class="__cf_email__" data-cfemail="315e4154435045585e5f505d425057544548715750501f565e47">[email&#160;protected]</span></a>. Any commentary that the FAA receives which 
is not specifically designated as CBI will be placed in the public 
docket for this rulemaking.

Background

    The FAA issued AD 2021-23-13, Amendment 39-21811 (86 FR 69992, 
December 9, 2021), (AD 2021-23-13), for all helicopters equipped with a 
radio altimeter. AD 2021-23-13 was prompted by a determination that 
radio altimeters cannot be relied upon to perform their intended 
function if they experience interference from wireless broadband 
operations in the 3.7-3.98 GHz frequency band (5G Lower C-Band). AD 
2021-23-13 required revising the limitations section of the existing 
RFM to incorporate limitations prohibiting certain operations requiring 
radio altimeter data when in the presence of 5G Lower C-Band 
interference as identified by Notices to Air Missions (NOTAMs). The 
agency issued AD 2021-23-13 because radio altimeter anomalies that are 
undetected by the automation or pilot, particularly close to the 
ground, could lead to loss of continued safe flight and landing.
    After the FAA issued AD 2021-23-13, the agency determined that 
additional limitations were needed due to the continued deployment of 
new 5G Lower C-Band base stations whose signals were expected to cover 
most of the contiguous United States at transmission frequencies 
between 3.7-3.98 GHz. Additionally, the FAA found that radio altimeter 
anomalies could lead to increased pilot workload and pilot 
desensitization to warnings. Therefore, the FAA issued AD 2023-11-07, 
Amendment 39-22453 (88 FR 40685, June 22, 2023) (AD 2023-11-07), to 
supersede AD 2021-23-13. For rotorcraft that are not radio altimeter 
tolerant rotorcraft, AD 2023-11-07 maintains the RFM limitations 
imposed by AD 2021-23-13 in areas identified by NOTAMs until June 30, 
2023. After June 30, 2023, for rotorcraft that are not radio altimeter 
tolerant rotorcraft, AD 2023-11-07 requires revising the RFM to 
incorporate the same limitations but with expanded coverage for 
operations in the entire contiguous U.S. airspace instead of only in 
areas identified by NOTAMs. AD 2023-11-07 also provides an option to 
modify the rotorcraft to become a radio altimeter tolerant rotorcraft 
in order to terminate the RFM limitations.

Actions Since AD 2023-11-07 Was Issued

    Since the FAA issued AD 2023-11-07, Transport Canada, which is the 
aviation authority for Canada, issued Transport Canada AD CF-2024-15, 
dated May 15, 2024 (the MCAI), to correct an unsafe condition for all 
helicopters equipped with a radio altimeter. The MCAI states that in 
July 2023, Innovation, Science and Economic Development Canada (ISED), 
Canada's spectrum regulator, published Standard Radio System Plans 
(SRSP)-520 Issue 3,\1\ and Radio Standard Specifications (RSS)-192 
Issue 5,\2\ which define the spectrum environment for the 3.45-3.90 GHz 
frequency band in

[[Page 64311]]

Canada. The MCAI further states that spectrum auctions for the 3.45-
3.65 GHz and the 3.65-3.9 GHz band were completed in 2021 and 2023, 
respectively.
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    \1\ <a href="https://ised-isde.canada.ca/site/spectrum-management-telecommunications/en/devices-and-equipment/standard-radio-system-plans/srsp-520-technical-requirements-fixed-andor-mobile-systems-including-flexible-use-broadband-systems">https://ised-isde.canada.ca/site/spectrum-management-telecommunications/en/devices-and-equipment/standard-radio-system-plans/srsp-520-technical-requirements-fixed-andor-mobile-systems-including-flexible-use-broadband-systems</a>.
    \2\ <a href="https://ised-isde.canada.ca/site/spectrum-management-telecommunications/en/devices-and-equipment/radio-equipment-standards/radio-standards-specifications-rss/rss-192-flexible-use-broadband-equipment-operating-band-3450-3900-mhz">https://ised-isde.canada.ca/site/spectrum-management-telecommunications/en/devices-and-equipment/radio-equipment-standards/radio-standards-specifications-rss/rss-192-flexible-use-broadband-equipment-operating-band-3450-3900-mhz</a>.
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    In July 2023, ISED implemented measures to mitigate Lower C-band 
interference to radio altimeters, which provide the Canadian airspace 
greater protection from 5G Lower C-band interference to radio 
altimeters as compared to the Lower C-band environment in the 
contiguous U.S. airspace. These measures include exclusion and 
protection zones and airport effective isotropic radiated power (EIRP) 
elevation mask (a restriction that requires nearby cell tower signals 
to be angled downward so they do not interfere with aircraft 
altimeters) at certain airport runways covering the majority of air 
traffic in Canada, as well as nationwide reduced fundamental power 
emissions based on the degree of antenna uptilt above the horizon to 
minimize emissions from 5G base stations toward aircraft.
    In late March 2026, Transport Canada notified the FAA that, 
beginning July 1, 2026, changes in the 5G Lower C-band protection 
mitigations established by ISED in 2023 would result in a more severe 
5G interference environment in the Canadian airspace. Exclusion and 
protection zones at airports will no longer exist and updates to the 
airport EIRP elevation mask, nationwide tilt restriction, emitter 
height limitation, and reduced spurious emissions will only protect 
rotorcraft that are radio altimeter tolerant. The change in mitigations 
will result in an unsafe condition in the Canadian 5G interference 
environment.
    Transport Canada determined that radio altimeters cannot be relied 
upon to perform their intended function if they experience interference 
from wireless broadband operations in the 3.45-3.98 GHz frequency band. 
Transport Canada based its determination on the same unsafe condition 
found by the FAA in AD 2023-11-07. As a result, the MCAI requires 
revising the limitations section of the existing RFM to incorporate 
limitations prohibiting certain operations requiring radio altimeter 
data, due to the presence of 5G Lower C-Band interference, while 
operating in Canadian airspace.
    As terminating action for the operating limitations, the MCAI 
provides that operators may modify their radio altimeters to 
demonstrate the tolerances for emissions as specified in the MCAI and 
AD 2023-11-07. You may examine the MCAI in the AD docket at 
<a href="http://regulations.gov">regulations.gov</a> under Docket No. FAA-2026-11799.
    The FAA is proposing this AD because radio altimeter anomalies that 
are undetected by the automation or pilot, particularly close to the 
ground, could lead to loss of continued safe flight and landing.

FAA's Determination

    The FAA is issuing this NPRM because the agency has determined the 
unsafe condition described previously is likely to exist or develop in 
other products of the same type design.

Proposed AD Requirements in This NPRM

    For non-radio altimeter tolerant rotorcraft: Before further flight 
in Canadian airspace, this proposed AD would require revising the 
existing RFM for the helicopter to incorporate limitations prohibiting 
the following when operating in Canadian airspace.
    <bullet> Performing approaches that require radio altimeter 
minimums for rotorcraft offshore operations. Barometric minimums must 
be used for these operations instead.
    <bullet> Engaging hover autopilot modes that require radio 
altimeter data.
    <bullet> Engaging Search and Rescue (SAR) autopilot modes that 
require radio altimeter data.
    <bullet> Performing takeoffs and landings in accordance with any 
procedure (Category A, Category B, or by Performance Class in the 
Rotorcraft Flight Manual or Operations Specification) that requires the 
use of radio altimeter data.
    This proposed AD provides that modifying the rotorcraft from a non-
radio altimeter tolerant rotorcraft to a radio altimeter tolerant 
rotorcraft terminates the RFM operating limitations.
    A rotorcraft that is a radio altimeter tolerant rotorcraft using a 
method approved by the FAA for AD 2023-11-07 is also a radio altimeter 
tolerant rotorcraft for the purposes of paragraph (g)(1) of this 
proposed AD.

Differences Between This Proposed AD and the MCAI

    The MCAI specifies the fundamental emissions are in the 3.45-3.98 
GHz frequency band, while this proposed AD specifies the 3.7-3.98 GHz 
frequency band. AD 2023-11-07 identified an unsafe condition from 
wireless broadband transmissions in the 3.7-3.98 GHz frequency band and 
this proposed AD is based on that same determination. In addition, 
rotorcraft determined to be a radio altimeter tolerant rotorcraft for 
the purposes of AD 2023-11-07, which has demonstrated the performance 
tolerances for fundamental emissions within the 3.7-3.98 GHz frequency 
band, would also be a radio altimeter tolerant rotorcraft for purposes 
of this proposed AD. Frequencies less than 3.7 GHz are further away 
from the frequency bands used by radio altimeters (4.2 to 4.4 GHz), so 
rotorcraft determined to be tolerant in the range of 3.7-3.98 GHz are 
also tolerant to emissions less than 3.7 GHz.

Interim Action

    The FAA considers this proposed AD to be an interim action. The FAA 
may consider further rulemaking if the Canadian 5G C-band interference 
environment changes or if Canada issues an operational rule to address 
5G C-band interference with radio altimeters.

Costs of Compliance

    The FAA notes that since operators must comply with this proposed 
AD before a rotorcraft's first flight in Canadian airspace, rotorcraft 
that do not operate in Canada will not have to comply and therefore 
will have no costs under this proposed AD.
    The FAA estimates that there are approximately 5,500 helicopters of 
U.S. registry that are likely to have a radio altimeter installed. The 
FAA also estimates that 1,128 of the 5,500 helicopters of U.S. registry 
are equipped to be able to perform the operations prohibited by this 
proposed AD for non-radio altimeter rotorcraft. While the FAA expects 
that some of the affected rotorcraft have been modified (either by 
replacing the radio altimeter or adding radio altimeter filters), the 
FAA does not have definitive data on how many rotorcraft have been 
become radio altimeter tolerant rotorcraft since July 2023, and 
therefore this proposed AD retains the estimates from AD 2023-11-07. 
The FAA estimates the following costs to comply with this proposed AD:

[[Page 64312]]



                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                     Cost per      Cost on U.S.
                Action                         Labor cost           Parts cost        product        operators
----------------------------------------------------------------------------------------------------------------
RFM revision for non-radio altimeter    1 work-hour x $85 per                 $0             $85        $467,500
 tolerant rotorcraft.                    hour = $85.
----------------------------------------------------------------------------------------------------------------

    The FAA estimates the following costs for operators who elect to 
modify their helicopter to be radio altimeter tolerant:

                                        Estimated Costs for Modification
----------------------------------------------------------------------------------------------------------------
                Action                        Labor cost               Parts cost            Cost per product
----------------------------------------------------------------------------------------------------------------
Modification (replacement)...........                                                    Up to $60,000 per
                                                                                          helicopter (includes
                                                                                          labor and parts).
Modification (filter)................  Up to 24 work-hours x    Up to $12,000..........  Up to $14,040 per
                                        $85 per hour = $2,040.                            filter.
----------------------------------------------------------------------------------------------------------------

Authority for This Rulemaking

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

Regulatory Findings

    The FAA determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD would 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 this proposed 
regulation:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Would not affect intrastate aviation in Alaska, and
    (3) Would not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

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

The Proposed Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

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

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


Sec.  39.13   [Amended]

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

Various Helicopters: Docket No. FAA-2026-11799; Project Identifier 
MCAI-2026-00594-R.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by November 23, 2026.

 (b) Affected ADs

    None.

 (c) Applicability

    This AD applies to all helicopters, certificated in any 
category, equipped with a radio (also known as radar) altimeter. 
These radio altimeters are installed on various helicopter models 
including, but not limited to, the helicopters for which the design 
approval holder is identified in paragraphs (c)(1) through (20) of 
this AD.

(1) Airbus Helicopters
(2) Airbus Helicopters Deutschland GmbH
(3) Air Space Design and Manufacturing, LLC
(4) Bell Textron Canada Limited
(5) Bell Textron Inc.
(6) Brantly International, Inc.
(7) Centerpointe Aerospace Inc.
(8) Columbia Helicopters, Inc.
(9) The Enstrom Helicopter Corporation
(10) Erickson Air-Crane Incorporated, DBA Erickson Air-Crane
(11) Helicopteres Guimbal
(12) Siam Hiller Holdings, Inc.
(13) Kaman Aerospace Corporation
(14) Leonardo S.p.a.
(15) MD Helicopters Inc.
(16) PZL-Swidnik S.A.
(17) Robinson Helicopter Company
(18) Schweizer RSG LLC
(19) Scotts-Bell 47 Inc.
(20) Sikorsky Aircraft Corporation

 (d) Subject

    Air Transport Association (ATA) of America Code 3444, Ground 
Proximity System.

(e) Unsafe Condition

    This AD was prompted by the 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 to 3.98 GHz frequency band (5G Lower C-Band) while operating in 
Canadian airspace. The FAA is issuing this AD because radio 
altimeter anomalies that are undetected by the automation or pilot, 
particularly while close to the ground, could lead to loss of 
continued safe flight and landing.

(f) Compliance

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

(g) Definitions

    (1) For purposes of this AD, a ``radio altimeter tolerant 
rotorcraft'' 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 rotorcraft.
    (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

[[Page 64313]]

specified in figure 1 to paragraph (g)(1)(i) of this AD.
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[GRAPHIC] [TIFF OMITTED] TP08OC26.028

    (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.

[[Page 64314]]

[GRAPHIC] [TIFF OMITTED] TP08OC26.029

BILLING CODE 4910-13-C
    (2) For purposes of this AD, a ``non-radio altimeter tolerant 
rotorcraft'' 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) Rotorcraft Flight Manual (RFM) Revision

    For non-radio altimeter tolerant rotorcraft: Before further 
flight in Canadian airspace, revise the Limitations Section of the 
existing RFM for the helicopter by including 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 RFM for the helicopter. The action required by this 
paragraph may be performed by the owner/operator (pilot) holding at 
least a private pilot certificate and must be entered into the 
aircraft records showing compliance with this AD in accordance with 
14 CFR 43.9(a)(1) through (4) and 14 CFR 91.417(a)(2)(v). The record 
must be maintained as required by 14 CFR 91.417 or 14 CFR 135.439.

[[Page 64315]]

[GRAPHIC] [TIFF OMITTED] TP08OC26.030

(i) Terminating Action for RFM Limitations

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

(j) 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 (k) of this AD. 
Information may be emailed to: <a href="/cdn-cgi/l/email-protection#ca8b8785898aacababe4ada5bc"><span class="__cf_email__" data-cfemail="b6f7fbf9f5f6d0d7d798d1d9c0">[email&#160;protected]</span></a>.
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the responsible Flight Standards Office.

(k) Additional Information

    For more information about this AD, contact Ken Fairhurst, 
Continued Operational Safety Technical Advisor, FAA, 2200 South 
216th St., Des Moines, WA 98198; phone: 817-222-5390; email: 
<a href="/cdn-cgi/l/email-protection#4c233c293e2d382523222d203f2d2a2938350c2a2d2d622b233a"><span class="__cf_email__" data-cfemail="5c332c392e3d283533323d302f3d3a3928251c3a3d3d723b332a">[email&#160;protected]</span></a>.

(l) Material Incorporated by Reference

    None.

    Issued on October 5, 2026.
Steven W. Thompson,
Acting Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2026-20677 Filed 10-7-26; 8:45 am]
BILLING CODE 4910-13-P


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