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The FAA is superseding a previous Airworthiness Directive for certain Diamond DA42 models which goes into effect in May. The 2022 AD required the replacement of the T-yoke axle with an improved rudder T-yoke axle and the superseding AD addresses an unsafe condition with reports of a loose rudder T-yoke axle nut, requiring inspections for correct installation of the self-locking nut to the T-yoke standard bolt, and dependent on findings, the replacement of the self-locking nut. If this condition is not corrected, it could lead to vertical movement of the bolt and reduce the plane's rudder control.
The initial AD went into effect on Dec. 14, 2022 and applied to Diamond Aircraft Industries GmbH Model DA42, DA42 NG and DA42 M-NG aircraft. Reports of loose rudder T-yoke axle nuts on DA42 planes led to an AD from the EASA, requiring repetitive inspections for correct installation of the self-locking nut and the FAA followed suit, issuing an AD for the same reported problem. The FAA said the EASA AD provided an optional terminating action for the repetitive inspections. In its Notice of Proposed Rulemaking, the FAA proposed requiring the inspection of the rudder steering bracket edge distance and, depending on the results of the inspection, inspecting the T-yoke bolt hole for wear and play, and performing corrective action if necessary. The NPRM proposed the repetitive inspection of torque seal marks on the rudder T-yoke bolt head for the proper alignment and the self-locking nut for proper installation, any necessary corrective action and prohibited the installation of affected parts.Read the FAA's Final Rule here
The FAA received comments from individuals and DAI. The individuals supported the NPRM without any changes and DAI requested the compliance time be changed from within 200 hours time-in-service or nine months after the effective date of the AD to within 200 flight hours or 12 months after the effective date of the AD. DAI told the FAA that the pilot and passenger seats would need to be removed before an inspection of the rudder steering bracket and installation of the improved T-yoke bolt and the removal of the seats is part of the plane's annual inspection. The company said that extending the compliance time from nine to 12 months would allow operators to align the AD requirements with the scheduled annual inspection and avoid unnecessary financial burdens for operators. DAI also said the formation of wear in the hole in the rudder steering bracket is related to the flight time, not a specific period of time. The company also emphasized that unnecessary maintenance actions should be avoided to avoid possible maintenance errors. The FAA agreed with the request, extending compliance time from nine to 12 months. The AD also specifies "within 200 hours time-in-service" since TIS is defined in the FAA regulations and used concerning maintenance records, and "flight hours" is not.
DAI also requested that rather than refer to specific steps in the work instructions in certain paragraphs of the AD, the entire work instructions be referred to. The company stated the importance of referencing the entire document and including all steps rather than specific steps due to the additional steps not addressed in some paragraphs of the AD. The FAA agreed to require the additional steps but did not agree to require compliance with the entire work instruction document. The AD requirements correspond with the EASA AD that only requires the following steps: inspecting the edge distance and repair if necessary, inspecting the hole and repair if required, replacing the affected part with a serviceable part, and marking the head of the T-yoke bolt and the self-locking nut. The FAA acknowledged that doing the additional steps was necessary to complete the actions required by the AD but to provide operators flexibility regarding how the steps are accomplished, the FAA does not require that operators follow all the steps in the work instructions.
Several other comments were addressed and revisions were made to language and requirements. DAI requested the requirement to apply torque seal marks in paragraph H and the FAA agreed, but instead of revising paragraph H, the agency revised paragraph I. The company also requested that certain paragraphs be revised to require operators to only contact DAI for post-inspection instructions, however, the FAA did not agree. The FAA acknowledged that not all discrepancies would result in a rudder steering bracket requiring replacement, but the agency said it cannot delegate repair approval authority to a single outside entity.
The recent AD, published in the Federal Register on April 22, will be effective May 28.