DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-2023; Project Identifier MCAI-2023-01246-T]
RIN 2120-AA64

Airworthiness Directives; 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 Bombardier, Inc., Model BD-100-1A10 airplanes. This
proposed AD was prompted by uncommanded horizontal stabilizer motion
during several in-service events caused by a problem with the trim
switch wiring. This proposed AD would require installing the pitch/roll
trim switch relays. 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 7,
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-2024-2023; 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 Bombardier material identified in this proposed AD,
contact Bombardier Business Aircraft Customer Response Center, 400
Cote-Vertu Road West, Dorval, Quebec H4S 1Y9, Canada;
phone 514-855-2999; email ac.yul@aero.bombardier.com; website
bombardier.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-2024-2023; Project Identifier
MCAI-2023-01246-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

Transport Canada, which is the aviation authority for Canada, has
issued Transport Canada AD CF-2023-77, dated December 7, 2023
(Transport Canada AD CF-2023-77) (also referred to after this as the
MCAI), to correct an unsafe condition on certain Bombardier, Inc.,
Model BD-100-1A10 airplanes. The MCAI states that during several in-
service events, following a STAB TRIM FAULT advisory message and an
auto-pilot disconnect, both pilot and co-pilot commands to trim the
horizontal stabilizer nose-up resulted in a nose-down movement of the
horizontal stabilizer. In some events, the horizontal stabilizer
reached the full travel nose-down position before the crew recognized
the nature of the problem, and quickly recovered control of the
airplane for safe landing. Transport Canada issued AD CF-2022-03, dated
February 1, 2022 (Transport Canada AD CF-2022-03) (which corresponds to
FAA AD 2022-12-02 (87 FR 34125, June 6, 2022)), as a mitigating action
to require the use of an Expanded Pitch Trim Pre-Flight Check, the use
of Trim Malfunction procedures, the revision of the AP STAB TRIM FAIL
caution and STAB TRIM FAULT advisory procedures to address this unsafe
condition. During the ongoing investigation by Bombardier and the
supplier of the horizontal stabilizer pitch/roll trim switch (trim
switch), Bombardier determined that one of the springs within the trim
switch had failed. The supplier of the spring was changed in 2019. The
majority of observed trim switch failures occurred in trim switches
that were manufactured after 2019. Consequently, Transport Canada
issued AD CF-2022-24, dated May 2, 2022 (Transport Canada AD CF-2022-
24) (which corresponds to FAA AD 2023-02-01 (88 FR 7856, February 7,
2023)), to remove and replace the defective springs in the affected
fleet. At that time, Bombardier also found an existing issue with the
trim switch wiring installation. The problem with the trim switch
wiring was identified as the main cause of the in-service unintended
horizontal stabilizer motion events. On this airplane model, manual
trim is accomplished by enabling the trim function by both pressing
down on the trim switch and simultaneously moving the switch up, down,
left, or right, as required to command trim in pitch or roll. The
current wiring of the system is such that an enable signal originating
from either the pilot-side or the copilot-side trim switch will enable
both sides. By design, the pilot-side trim commands have priority over
the copilot-side trim commands. Thus, if trim is enabled via the
copilot-side trim switch, and the pilot-side trim switch malfunctions,
it is possible for trim to move uncommanded or opposite to the intended
direction. Transport Canada AD CF-2023-77 requires changes to the trim
switch wiring installation to ensure the pilot and co-pilot trim
Enable/Arm switch signals remain segregated in both roll and pitch
axes.
The FAA is proposing this AD to address the problem with the trim
switch wiring, which is the main cause of the uncommanded horizontal
stabilizer motion. The unsafe condition, if not addressed, could result
in increased crew workload and reduced safety margins, and if the
flightcrew is unable to regain control of the horizontal stabilizer,
would result in loss of control of the airplane and high control
forces.
You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2024-2023.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Bombardier Service Bulletin 100-27-22 and
Bombardier Service Bulletin 350-27-012, both dated December 29, 2022.
The material specifies procedures to install the pitch/roll trim switch
relays. The installation includes reworking the plate assembly; installing relay
bracket assemblies, relays, ground return stacks on the relay bracket
assemblies, wires for the relays, and line replaceable units and trays
on the left-side and right-side avionic racks; and performing
operational testing. These documents are distinct since they apply to
different airplane serial numbers.
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 and
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.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 359 airplanes of U.S. registry. The FAA estimates the following
costs to comply with this proposed AD:

Estimated Costs for Required Actions

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: