DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-1896; Project Identifier MCAI-2023-00978-T]
RIN 2120-AA64

Airworthiness Directives; MHI RJ Aviation ULC (Type Certificate
Previously Held by Bombardier Inc.) Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain MHI RJ Aviation ULC Model CL-600-2B19 (Regional Jet Series
100 and 440), CL-600-2C10 (Regional Jet Series 700, 701, and 702), CL-
600-2C11 (Regional Jet Series 550), CL-600-2D15 (Regional Jet Series
705), CL-600-2D24 (Regional Jet Series 900), and CL-600-2E25 (Regional
Jet Series 1000) airplanes. AD 2023-10-02 was prompted by the
determination that radio altimeters cannot be relied on to perform
their intended function if they experience interference from wireless
broadband operations in the 3.7-3.98 GHz frequency band (5G C-Band).
This AD was prompted by the determination that this interference can
also result in certain failure messages being inhibited longer than
intended. This proposed AD would require installing a new radio
frequency (RF) bandpass filter on the coaxial line between the radio
altimeter and the receive antenna in the aft equipment compartment. 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 October 24,
2024.

ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to regulations.gov. Follow
the instructions for submitting comments.
Fax: 202-493-2251.
Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.
Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-1896; 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.
Material Incorporated by Reference:
For MHI RJ material identified in this proposed AD,
contact MHI RJ Aviation Group, Customer Response Center, 3655 Ave. des
Grandes-Tourelles, Suite 110, Boisbriand, Quebec J7H 0E2 Canada;
North America toll-free telephone 833-990-7272 or direct-dial telephone
450-990-7272; fax 514-855-8501; email thd.crj@mhirj.com; website
mhirj.com.
You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 2200 South 216th St., Des
Moines, WA. For information on the availability of this material at the
FAA, call 206-231-3195.

FOR FURTHER INFORMATION CONTACT: Steven Dzierzynski, Aviation Safety
Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590;
telephone 516-228-7300; email 9-avs-nyaco-cos@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under ADDRESSES. Include ``Docket No. FAA-2024-1896; Project Identifier
MCAI-2023-00978-T'' 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 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
Steven Dzierzynski, Aviation Safety Engineer, FAA, 1600 Stewart Avenue,
Suite 410, Westbury, NY 11590; telephone 516-228-7300; email
9-avs-nyaco-cos@faa.gov. Any commentary that the FAA receives that is not
specifically designated as CBI will be placed in the public docket for
this rulemaking.

Background

The FAA issued AD 2023-10-02, Amendment 39-22438 (88 FR 34065, May
26, 2023) (AD 2023-10-02) to address the effect of interference from
wireless broadband operations in the 5G C-Band on all transport and
commuter category airplanes equipped with a radio altimeter. AD 2023-
10-02 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 5G C-Band. AD
2023-10-02 requires revising the limitations section of the existing
airplane flight manual to incorporate limitations prohibiting transport
and commuter category airplanes from performing certain low-visibility
landing operations at any airport unless they have upgraded their radio
altimeters. Transport Canada, which is the aviation authority for
Canada, issued corresponding Transport Canada AD CF-2023-46, dated June
30, 2023, to require similar limitations on flight operations requiring
radio altimeter data in U.S. airspace affected by 5G C-Band wireless
signals.
Additionally, Transport Canada has issued Transport Canada AD CF-
2023-62R1, dated November 21, 2023 (referred to as ``the MCAI''), for
certain serial-numbered MHI RJ Aviation ULC Model CL-600-2B19 (Regional
Jet Series 100 and 440), CL-600-2C10 (Regional Jet Series 700, 701, and
702), CL-600-2C11 (Regional Jet Series 550), CL-600-2D15 (Regional Jet
Series 705), CL-600-2D24 (Regional Jet Series 900), and CL-600-2E25
(Regional Jet Series 1000) airplanes. The MCAI states that, in addition
to the effects of 5G C-Band broadband interference identified in FAA AD
2023-10-02, MHI RJ has determined that 5G C-Band broadband interference
can result in certain failure messages and aural alerts being inhibited
longer than intended. Specifically, this can result in the inhibition
of hydraulic system #3 and wing anti-ice overheat failure messages such
that flightcrew are unable to perform appropriate airplane flight
manual (AFM) procedures in the time needed to prevent loss of elevator
control due to hydraulic system overheat and wing structural damage due
to wing anti-ice system overheat. This condition, if not corrected,
could result in delayed flightcrew response leading to loss of
continued safe flight and landing.
The MCAI requires the installation of a new RF bandpass filter on
the coaxial line between the radio altimeter and the receive antenna in
the aft equipment compartment. For airplanes with a dual radio
altimeter configuration, the MCAI requires a filter to be installed on
both systems or on one system provided the second system is
deactivated. When the airplane is modified as specified in the MCAI,
the configuration with the RF bandpass filter installed has been
determined to be ``radio altimeter tolerant.'' The actions of the MCAI
apply only to airplanes operating within the contiguous U.S. airspace.
The FAA is proposing this AD because radio altimeter anomalies can
result in the inhibition of certain failure messages such that the
flightcrew are unable to perform appropriate AFM procedures in the time
needed to prevent loss of elevator control due to hydraulic system
overheat and wing structural damage due to wing anti-ice system
overheat, possibly resulting in delayed flightcrew response leading to
loss of continued safe flight and landing.
You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2024-1896.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed MHI RJ Service Bulletins 601R-34-152, Revision D,
dated May 11, 2023, and 670BA-34-054, dated February 20, 2023. This
material specifies procedures for installing a new RF bandpass filter
on the coaxial line between the radio altimeter and the receive antenna
in the aft equipment compartment. These documents are distinct since
they apply to different airplane models. This material is reasonably
available because the interested parties have access to it through
their normal course of business or by the means identified in the
ADDRESSES section.

FAA's Determination

This product has been approved by the aviation authority of another
country and is approved for operation in the United States. Pursuant to
the FAA's bilateral agreement with this State of Design Authority, it
has notified the FAA of the unsafe condition described in the material
referenced above. The FAA is issuing this NPRM after determining that
the unsafe condition described previously is likely to exist or develop
on other products of the same type design.

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified
in the material already described. This AD would not apply to airplanes
that have been modified to be a radio altimeter tolerant airplane under
the requirements of AD 2023-10-02.

Differences Between the MCAI and This NPRM

Although the actions of the MCAI apply only to Canadian-registered
airplanes operating within the contiguous U.S. airspace, this proposed
AD would apply to U.S.-registered airplanes operating in any airspace.
The FAA has determined that the expansion of 5G C-band has occurred in
other countries, such as Canada and Brazil, in which 5G C-band
interference is expected.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect up to 873 airplanes of U.S. registry. However, many of these
airplanes may already have a bandpass filter installed in compliance
with AD 2023-10-02 and would not have any costs because of this
proposed AD. The FAA estimates the following costs to comply with this
proposed AD:

Estimated Costs

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

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]

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