DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-0227; Project Identifier MCAI-2023-00886-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-700-2A12 airplanes. This
proposed AD was prompted by a report indicating that the fan in a
transformer rectifier unit (TRU) can become inoperative in a manner
that is not detectable by the fan monitoring circuit. This proposed AD
would require replacement of the existing TRU Number 2 with a new part
number that incorporates a correction to the fan and the monitoring
circuit. This proposed AD would also prohibit the installation of
affected parts. 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 April 1,
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-2024-0227; 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 service information identified in this NPRM, contact
Bombardier Business Aircraft Customer Response Center, 400 C[ocirc]te-
Vertu Road West, Dorval, Qu[eacute]bec H4S 1Y9, Canada; telephone 514-
855-2999; email ac.yul@aero.bombardier.com; website bombardier.com.
You may view this service information 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: William Reisenauer, 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-2024-0227; Project Identifier
MCAI-2023-00886-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
William Reisenauer, 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-2023-53, dated July 14, 2023 (Transport
Canada AD CF-2023-53) (also referred to after this as the MCAI), to
correct an unsafe condition on certain Bombardier, Inc., Model BD-700-
2A12 airplanes. The MCAI states that the fan in a TRU can become
inoperative in a manner that is not detectable by the fan monitoring
circuit. An inoperative fan leads to higher TRU operating temperatures,
which can trigger the activation of the load shed function to reduce
the electrical load and temperature in the TRU. If the TRU temperature
continues to rise and exceeds the maximum temperature threshold, the
TRU will automatically disconnect. The shed electrical load will be
transferred to the remaining two TRUs, which could lead to overheating
and cascading failures on the remaining TRUs.
In addition, a design issue was uncovered where the fan power-up
built-in test (PBIT) and continuous built-in-test (CBIT) are not
adequate to detect fan failure. The fan PBIT is a test that is
automatically performed once the airplane is powered up. The fan PBIT
initiates the fan to turn on regardless of the TRU temperature to test
the fan's functionality. The fan CBIT detects fan failure during
airplane operation. Therefore, if FAN PBIT and/or CBIT are not reliable
to detect a fan failure, inoperative fan conditions will remain
dormant.
It was also identified that an insulation blanket located close to
the TRU 2 fan air inlet may be leading to an eventual reduction of TRU
2 cooling efficiency.
The FAA is proposing this AD to address the inability of a TRU to
detect the fan failure. The unsafe condition, if not addressed, could
lead to overheating and failures on the remaining TRUs, which could
contribute to additional pilot workload and adversely affect the safe
operation of the airplane.
You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2024-0227.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Bombardier Service Bulletin 700-24-7507, Revision
1, dated May 19, 2023. This service information specifies procedures
for replacing the existing transformer rectifier unit (TRU) Number 2
part number (P/N) G02404521-001 with new P/N G02404521-003, including
removal of the secondary layer of insulation blanket P/N ENM386519113D
in front of the TRU Number 2 fan air inlet, re-identifying the blanket
installation by ink stamp, checking the electrical bond resistance for
TRU Number 2, and performing the operational test.
This service information 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
service information 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 service information already described, except as discussed under
``Difference Between this NPRM and the Service Information.'' This
proposed AD would also prohibit the installation of affected parts.

Difference Between This NPRM and Service Information

This AD does not require replacing the existing essential TRU P/N
G02404521-001 with new P/N G02404521-003, as specified in Bombardier
Service Bulletin 700-24-7507, Revision 1, dated May 19, 2023. TRU
Number 2 has a higher electrical load than the essential TRU and,
therefore, is more susceptible to the fan inoperative condition.
Replacement of TRU Number 2, as specified in this proposed AD, will
adequately address the safety concern.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 56 airplanes of U.S. registry. The FAA estimates the following
costs to comply with this proposed AD:

Estimated Costs for Required Actions

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some or all 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: