DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-0227; Project Identifier MCAI-2023-00886-T;
Amendment 39-22838; AD 2024-18-04]
RIN 2120-AA64

Airworthiness Directives; Bombardier, Inc., Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain Bombardier, Inc., Model BD-700-2A12 airplanes. This 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 AD requires replacement of the
existing TRU Number 2 with a new part number that incorporates a
correction to the fan and the monitoring circuit. This AD also
prohibits the installation of affected parts. The FAA is issuing this
AD to address the unsafe condition on these products.

DATES: This AD is effective November 12, 2024.

The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of November 12, 2024.

ADDRESSES:

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 final rule, the mandatory continuing airworthiness
information (MCAI), any comments received, and other information. The
address for Docket Operations is U.S. Department of Transportation,
Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200
New Jersey Avenue SE, Washington, DC 20590.

Material Incorporated by Reference:

For Bombardier material identified in this AD, contact
Bombardier Business Aircraft Customer Response Center, 400 Cote-
Vertu Road West, Dorval, Quebec H4S 1Y9, Canada; telephone 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. It is also available at regulations.gov under
Docket No. FAA-2024-0227.

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:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to certain Bombardier,
Inc., Model BD-700-2A12 airplanes. The NPRM published in the Federal
Register on February 14, 2024 (89 FR 11228). The
NPRM was prompted by AD CF-2023-53, dated July 14, 2023, issued by
Transport Canada, which is the aviation authority for Canada (referred
to after this as the MCAI). 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 the NPRM, the FAA proposed to require replacement of the
existing TRU Number 2 with a new part number that incorporates a
correction to the fan and the monitoring circuit. The NPRM also
proposed to prohibit the installation of affected parts. The FAA is
issuing 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.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from NetJets Inc. The following presents
the comments received on the NPRM and the FAA's response to the
comments.

Request To Update the Service Bulletin to the Latest Revision

NetJets requested that paragraphs (g) and (i) of the proposed AD be
revised to change Bombardier Service Bulletin 700-24-7507, Revision 1,
dated May 19, 2023, to Bombardier Service Bulletin 700-24-7507,
Revision 2, dated October 16, 2023.

The FAA agrees with the request. For airplanes on which the actions
of Revision 1 of the service bulletin have already been done, no more
work is required by Revision 2. The FAA clarified with Bombardier that
credit can be given for the accomplishment of actions specified in
Bombardier Service Bulletin 700-24-7507, Revision 1, dated May 19,
2023. The FAA has therefore revised this AD to require Revision 2 and
to add credit in paragraph (i) of this AD for accomplishment of the
actions specified in Bombardier Service Bulletin 700-24-7507, Revision
1, dated May 19, 2023, if completed before the effective date of this AD.

Request for Allowance To Install Part Number G02404521-001 for TRU
Number 1 and Number 3

NetJets noted that the Bombardier Service Bulletin 700-24-7507,
Revision 2, dated October 16, 2023, limits the installation of TRU part
number (P/N) G02404521-001 to the Number 2 position. NetJets requested
that an exception be added to paragraph (h) of the proposed AD to also
allow the installation of TRU P/N G02404521-001 for TRU Number 1 and
TRU Number 3.

The FAA does not agree to allow installation of TRU P/N G02404521-
001 for TRU Number 1 or Number 3. The TRU P/N G02404521-001 design
fails to detect a fan failure. Bombardier Service Bulletin 700-24-7507,
Revision 2, dated October 16, 2023, replaces only TRU Number 2 position
because it has a higher electrical load and is more susceptible to the
fan inoperative condition. TRU P/N G02404521-001 is no longer
manufactured. The new production airplanes are all installed with TRU
P/N G02404521-003. All TRUs that are removed from service (e.g., for
repair) are upgraded to TRU P/N G02404521-003. Therefore, this AD has
not been changed regarding this request.

Conclusion

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 reviewed the relevant data, considered the
comment received, and determined that air safety requires adopting this
AD as proposed. Accordingly, the FAA is issuing this AD to address the
unsafe condition on this product. Except for minor editorial changes,
and any other changes described previously, this AD is adopted as
proposed in the NPRM. None of the changes will increase the economic
burden on any operator.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Bombardier Service Bulletin 700-24-7507, Revision
2, dated October 16, 2023. This material specifies procedures for
replacing the existing TRU Number 2 P/N G02404521-001 with new P/N
G02404521-003, including removal of the secondary layer of insulation
blanket ENM386519113C or P/N ENM386519113D in front of the TRU Number 2
fan air inlet, reidentifying the blanket installation by ink stamp,
checking the electrical bond resistance for TRU Number 2, and
performing the operational test.

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.

Costs of Compliance

The FAA estimates that this AD affects 56 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this 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
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

This AD will not have federalism implications under Executive Order
13132. This AD will 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 that this AD:

(1) Is not a "significant regulatory action" under Executive
Order 12866,

(2) Will not affect intrastate aviation in Alaska, and

(3) Will 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 Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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: