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###### Department of Transportation

###### Federal Aviation Administration

          - 14 CFR Part 39
          - [Docket No. FAA-2021-1017; Product Identifier AD-2021-00495-A]
          - RIN 2120-AA64

# AGENCY:

Federal Aviation Administration (FAA), DOT.

# ACTION:

Proposed rule; withdrawal.

# SUMMARY:

                        The FAA is withdrawing a notice of proposed rulemaking (NPRM) that proposed to adopt a new airworthiness directive (AD) for all True Flight Holdings LLC Model AA-1, AA-1A, AA-1B, AA-1C, AA-5, AA-5A, and AA-5B airplanes. The NPRM was prompted by the report of an accident of an airplane with bondline corrosion and delamination of the horizontal stabilizers. The NPRM proposed to require inspecting the wings, fuselage,                               ( print page 22145)                            and stabilizers for bondline separation, corrosion, and previous repair. The NPRM also proposed to require repairing or replacing parts and applying corrosion inhibitor as necessary. Since issuance of the NPRM, the FAA has determined that there is not an unsafe condition, but instead incorrectly followed maintenance procedures. Accordingly, the NPRM is withdrawn.                    

# DATES:

                        As of April 14, 2022, the proposed rule, which published in the                         **Federal Register**                         on December 1, 2021 (86 FR 68171), is withdrawn.                    

# ADDRESSES:

## Examining the AD Docket

                    You may examine the AD docket at                     *https://www.regulations.gov*                     by searching for and locating Docket No. FAA-2021-1017; 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 AD action, any comments received, and other information. The street 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.                

# FOR FURTHER INFORMATION CONTACT:

                        Fred Caplan, Aviation Safety Engineer, Atlanta ACO Branch, FAA, 1701 Columbia Avenue, College Park, GA 30337; phone: (404) 474-5507; email:                         *frederick.n.caplan@faa.gov*.                    

# SUPPLEMENTARY INFORMATION:

## Background

The FAA issued AD 2021-14-12, Amendment 39-21639 (86 FR 36491, July 12, 2021) (AD 2021-14-12), for True Flight Holdings LLC Model AA-1, AA-1A, AA-1B, AA-1C, and AA-5 airplanes. AD 2021-14-12 was prompted by an accident involving a Model AA-5 airplane that occurred on January 19, 2021. During flight, the outboard elevator attach bracket on the horizontal stabilizer detached, causing loss of elevator control and significant damage to the airplane. An investigation identified corrosion and delamination of the airplane skin bondlines around the area of the horizontal stabilizer where the elevator attach bracket was attached. Multiple field reports identified additional instances of corrosion and delamination of skin bondlines around the horizontal stabilizer and other primary structures.

AD 2021-14-12 stated that Model AA-1, AA-1A, AA-1B, AA-1C, and AA-5 airplanes have horizontal stabilizers that are similar in design and use the same metal-to-metal bonding process. While the bond adhesive remains structurally sound throughout the aging process, factors such as corrosion and freezing moisture may compromise the structural integrity of some of the bond joints. This can lead to delamination of the skin from the primary structure. The FAA determined that a more thorough inspection was necessary to reliably identify corrosion and delamination of bondlines in these critical areas, including the horizontal stabilizer. As a result, AD 2021-14-12 requires a one-time inspection of the horizontal stabilizers, paying particular attention to the bondlines, for cracks, buckles, corrosion, delamination, rust, or previous repair.

                    The FAA issued an NPRM that proposed to amend 14 CFR part 39 by adding an AD for all True Flight Holdings LLC Model AA-1, AA-1A, AA-1B, AA-1C, AA-5, AA-5A, and AA-5B airplanes. The NPRM published in the                     **Federal Register**                     on December 1, 2021 (86 FR 68171). In the NPRM, the FAA proposed to require a repetitive inspection of the wings, stabilizers, and aft fuselage for bondline separation, corrosion, and previous repair. While AD 2021-14-12 requires only inspecting the bondlines on the horizontal stabilizers, in the NPRM, the FAA proposed to require inspecting all of the bondlines on the airplane, including the bondlines on the wings and aft fuselage. In the NPRM, the FAA also proposed to add Model AA-5A and AA-5B airplanes to the applicability due to the similar bonded construction of all models.                

The original decision to pursue corrective action was based upon multiple field reports, including direct observation of two airplanes, of issues related to inspection of bonded structure. The first was the originating accident airplane, and the second was another same model airplane located in the same hangar as the first airplane. Both of these airplanes exhibited damage (bondline delamination) in an area believed to be the source of the accident, at the attachment of the elevator bearing to the horizontal stabilizer. The construction in this area is similar among the applicable models in AD 2021-14-12. The issue specific to this area was addressed in AD 2021-14-12.

The FAA proposed the NPRM to address inspection for bondline delamination on the entire airplane based on an understanding that standard maintenance actions were insufficient to detect an issue. Because more models than those covered by AD 2021-14-12 share a similar bonded construction for the airplane as a whole, the NPRM proposed to also apply to True Flight Holdings LLC Model AA-5A and AA-5B airplanes.

## Comments

The FAA received comments from 41 commenters. The commenters were the Aircraft Owners and Pilots Association (AOPA), the Grumman Owners & Pilots Association (GOPA), Fortnight Aviation Maintenance, and many individual airplane owners and pilots.

All commenters opposed the NPRM. Most commenters stated that the actions proposed in the NPRM are already addressed by existing maintenance practices or included in maintenance documents such as the Grumman maintenance manual, the annual inspection checklist, service bulletins, and AD 2021-14-12. The commenters noted that the January 2021 accident resulted from poor maintenance practices and failure to adequately follow these existing procedures, not from any fault with the procedures themselves. For this reason, some commenters requested the FAA withdraw the NPRM due to lack of supporting data and issue a special airworthiness information bulletin (SAIB) instead.

Several commenters requested that the FAA remove Model AA-5, AA-5A, and AA-5B airplanes from the applicability because these models have a different design than the accident airplane. Many commenters noted that the proposed AD is overly broad because the delamination issue is limited to pre-1977 models manufactured with a “purple glue” for adhesive. AOPA, GOPA, and a few individuals stated the proposed requirement to tap test all bondlines on the airplane annually would damage the paint and lead to corrosion. Lastly, AOPA, GOPA, and two individuals requested the FAA increase its estimated labor rate of $85 per hour.

                    The FAA agrees that the instructions in the airplane maintenance manual are sufficient to detect the type of damage that is believed to have led to the originating accident, as well as similar damage on the rest of the airplane. The FAA further agrees that the original findings were not indicative of an unsafe condition, but instead indicative of incorrectly followed maintenance procedures. Based on this assessment, the proposed inspection in the NPRM would exceed what is sufficient to detect the main issue of bondline delamination. The FAA has determined that additional AD action is not warranted and the proposal should be withdrawn.                          ( print page 22146)    

The FAA acknowledges the comments unrelated to whether there is an unsafe condition. However, because the FAA is withdrawing the NPRM, those commenters' requests are no longer necessary.

Withdrawal of the NPRM constitutes only such action and does not preclude the FAA from further rulemaking on this issue, nor does it commit the FAA to any course of action in the future.

## Regulatory Findings

Since this action only withdraws an NPRM, it is neither a proposed AD nor a final rule. This action, therefore, is not covered under Executive Order 12866 or the Regulatory Flexibility Act.

# List of Subjects in 14 CFR Part 39

      - Air transportation
      - Aircraft
      - Aviation safety
      - Safety

## The Withdrawal

                    Accordingly, the notice of proposed rulemaking, Docket No. FAA-2021-1017; Project Identifier AD-2021-00495-A, published in the                     **Federal Register**                     on December 1, 2021 (86 FR 68171), is withdrawn.                

Issued on April 7, 2022.

Lance T. Gant,

Director, Compliance & Airworthiness Division, Aircraft Certification Service.

[FR Doc. 2022-07871 Filed 4-13-22; 8:45 am]

BILLING CODE 4910-13-P