2024-02948. Airworthiness Directives; Bombardier, Inc., Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

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: [phone].

• 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 Côte-Vertu Road West, Dorval, Québec H4S 1Y9, Canada; telephone [phone]; email [e-mail]; 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 [phone]; email [e-mail].

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 [phone]; email [e-mail]. 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

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.

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.

§ 39.13

[Amended]

2. The FAA amends § 39.13 by adding the following new airworthiness directive:

Bombardier, Inc.: Docket No. FAA–2024–0227; Project Identifier MCAI–2023–00886–T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by April 1, 2024.

(b) Affected ADs

None.

(c) Applicability

This AD applies to Bombardier, Inc., Model BD–700–2A12 airplanes, certificated in any category, serial numbers 70006 through 70166 inclusive.

(d) Subject

Air Transport Association (ATA) of America Code 24, Electrical power.

(e) Unsafe Condition

This AD was prompted by a report that the fan in a transformer rectifier unit (TRU) can become inoperative in a manner that is not detectable by the fan monitoring circuit. 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.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Transformer Rectifier Unit (TRU) Number 2 Replacement

Within 1,500 flight hours or 3 years, whichever occurs first after the effective date of this AD, replace TRU Number 2 part number (P/N) G02404521–001 with P/N G02404521–003, in accordance with the Accomplishment Instructions of Bombardier Service Bulletin 700–24–7507, Revision 1, dated May 19, 2023.

(h) Parts Installation Prohibition

As of the effective date of this AD, no person may install, on any airplane, a TRU part number G02404521–001.

(i) Credit for Previous Actions

This paragraph provides credit for actions required by paragraph (g) of this AD, if those actions were performed before the effective date of this AD using in accordance with Bombardier Service Bulletin 700–24–7507, dated March 31, 2023.

(j) Special Flight Permits

Special flight permits may be issued in accordance with 14 CFR 21.197 and 21.199 to operate the airplane to a location where the actions required by this AD can be accomplished, provided no passengers are on board, only essential crew, and day visual flight rules.

(k) Additional AD Provisions

The following provisions also apply to this AD:

(1) Alternative Methods of Compliance (AMOCs): The Manager, International Validation Branch, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or responsible Flight Standards Office, as appropriate. If sending information directly to the manager of the International Validation Branch, mail it to the address identified in paragraph (l)(2) of this AD. Information may be emailed to: [e-mail]. Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards Office.

(2) Contacting the Manufacturer: For any requirement in this AD to obtain instructions from a manufacturer, the instructions must be accomplished using a method approved by the Manager, International Validation Branch, FAA; or Transport Canada or Bombardier, Inc.'s Transport Canada Design Approval Organization (DAO). If approved by the DAO, the approval must include the DAO-authorized signature.

(l) Additional Information

(1) Refer to Transport Canada AD CF–2023–53, dated July 14, 2023, for related information. This Transport Canada AD may be found in the AD docket at regulations.gov under Docket No. FAA–2024–0227.

(2) For more information about this AD, contact William Reisenauer, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; telephone [phone]; email [e-mail].

(3) Service information identified in this AD that is not incorporated by reference is available at the addresses specified in paragraphs (m)(3) and (4) of this AD.

(m) Material Incorporated by Reference

(1) The Director of the Federal Register approved the incorporation by reference (IBR) of the service information listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this service information as applicable to do the actions required by this AD, unless this AD specifies otherwise.

(i) Bombardier Service Bulletin 700–24–7507, Revision 1, dated May 19, 2023.

(ii) [Reserved]

(3) For service information identified in this AD, contact Bombardier Business Aircraft Customer Response Center, 400 Côte-Vertu Road West, Dorval, Québec H4S 1Y9, Canada; telephone [phone]; email [e-mail]; website bombardier.com.

(4) 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.

(5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, visit www.archives.gov/​federal-register/​cfr/​ibr-locations, or email [e-mail].

Issued on February 7, 2024.

Victor Wicklund,

Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.