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AGENCY:
Federal Aviation Administration (FAA), DOT.
ACTION:
Final rule.
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 Côte-Vertu Road West, Dorval, Québec H4S 1Y9, Canada; telephone 514-855-2999; emailac.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 atregulations.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
| Labor cost | Parts cost | Cost per product | Cost on U.S. operators |
|---|---|---|---|
| Up to 5 work-hours × $85 per hour = Up to $425 | Up to $34,754 | Up to $35,179 | Up to $1,970,024. |