DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2025-0619; Project Identifier MCAI-2024-00372-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 all MHI RJ Aviation ULC Model CL-600-2C10 (Regional Jet Series 700,
701 & 702), CL-600-2C11 (Regional Jet Series 550), Model CL-600-2D15
(Regional Jet Series 705), CL-600-2D24 (Regional Jet Series 900), and
CL-600-2E25 (Regional Jet Series 1000). This proposed AD was prompted
by an engine indicating and crew alerting system (EICAS) STAB TRIM
Caution message that was posted, and subsequent repair that found
prematurely worn teeth on a rubber bull gear (RBG) wheel in the
horizontal stabilizer trim actuator (HSTA). This proposed AD would
require an inspection for part numbers and on-condition replacement of
affected RBG wheels and prohibit the installation of affected parts
under certain conditions, as specified in a Transport Canada AD, which
is proposed for incorporation by reference (IBR). 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 May 30, 2025.

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-2025-0619; 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 Transport Canada material identified in this proposed
AD, contact Transport Canada, Transport Canada National Aircraft
Certification, 159 Cleopatra Drive, Nepean, Ontario K1A 0N5, Canada;
telephone 888-663-3639; email TC.AirworthinessDirectives-Consignesdenavigabilite.TC
@tc.gc.ca. You may find this material on the Transport Canada website
at tc.canada.ca/en/aviation. It is also available at regulations.gov under
Docket No. FAA-2025-0619.

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: Isabel Saltzman, 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 the ADDRESSES section. Include "Docket No. FAA-2025-0619;
Project Identifier MCAI-2024-00372-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 this 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
Isabel Saltzman, 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 which is not
specifically designated as CBI will be placed in the public docket for
this rulemaking.

Background

Transport Canada, which is the aviation authority for Canada, has
issued Transport Canada AD CF-2024-25, dated June 28, 2024 (Transport
Canada AD CF-2024-25) (also referred to as the MCAI), to correct an
unsafe condition for all MHI RJ Aviation ULC Model CL-600-2C10
(Regional Jet Series 700, 701 & 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 an in-service event occurred where an EICAS STAB TRIM
Caution message was posted. Following the occurrence, the HSTA was
removed and returned to the vendor for repair. During repair, it was
discovered that one of the two RBG wheels had worn teeth. Investigation
revealed quality issues involving the machining and surface treatment
of the HSTA RBG wheel had caused premature wear of the wheel teeth.
Further investigation determined that this quality issue affects a
limited number of RBG wheels and HSTA serial numbers. Wear of the RBG
wheel teeth could cause a failure of the horizontal stabilizer trim system.

The FAA is proposing this AD to address the unsafe condition on
these products.

You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2025-0619.

Material Incorporated by Reference Under 1 CFR Part 51

Transport Canada AD CF-2024-25 specifies procedures for a part
number check and, if necessary, replacement of affected RBG wheels in
certain HSTAs. Transport Canada AD CF-2024-25 also prohibits the
installation of affected parts under certain conditions. 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 MCAI
referenced above. The FAA is issuing this NPRM after determining that
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

This proposed AD would require accomplishing the actions specified
in Transport Canada AD CF-2024-25 described previously, except for any
differences identified as exceptions in the regulatory text of this
proposed AD.

Explanation of Required Compliance Information

In the FAA's ongoing efforts to improve the efficiency of the AD
process, the FAA developed a process to use some civil aviation
authority (CAA) ADs as the primary source of information for compliance
with requirements for corresponding FAA ADs. The FAA has been
coordinating this process with manufacturers and CAAs. As a result, the
FAA proposes to incorporate Transport Canada AD CF-2024-25 by reference
in the FAA final rule. This proposed AD would, therefore, require
compliance with Transport Canada AD CF-2024-25 in its entirety through
that incorporation, except for any differences identified as exceptions
in the regulatory text of this
proposed AD. Material required by Transport Canada AD CF-2024-25 for
compliance will be available at regulations.gov under Docket No. FAA-
2025-0619 after the FAA final rule is published.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 460 airplanes of U.S. registry. The FAA estimates the following
costs to comply with this proposed AD:

Estimated Costs for Required Actions

The FAA estimates the following costs to do any necessary on-
condition action that would be required based on the results of any
required actions. The FAA has no way of determining the number of
aircraft that might need this on-condition action:

Estimated Costs of On-Condition Actions

* The FAA has received no definitive data on which to base the cost
estimates for the on-condition parts specified in this proposed AD.

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some or all of the costs of
this proposed AD may be covered under warranty, thereby reducing the
cost impact on affected operators.

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: