AD 2021-22-11 Requires A One-Time Visual And Recurring Borescope Inspections Of The Torque Tube

The FAA is adopting a new airworthiness directive (AD) for certain MD Helicopters Inc. (MDHI), Model 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, and 600N helicopters.

This AD was prompted by a report of a spiral crack in the pilot-to-copilot tail rotor torque tube (torque tube). This AD requires a one-time visual and recurring borescope inspections of the torque tube and depending on the results, removing the torque tube from service. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective January 10, 2022.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to MDHI Model 369D, 369E, 369F, 369FF, 369H, 369HE, 369HM, 369HS, 500N, and 600N helicopters, with torque tube part number 369H7531-9/-11/-13, installed. The NPRM published in the Federal Register on August 13, 2021 (86 FR 44652). In the NPRM, the FAA proposed to initially require visually inspecting the torque tube exterior using a flashlight and mirror and borescope inspecting the interface of the torque tube and bushing segments for a crack, elongation, and other damage, which may be indicated by any corrosion, pitting, crazing, dents, dings, displacement of material at the bolt hole edge, or fretting of the hole. Thereafter, the NPRM proposed to require repeating the borescope inspection. If there is a crack, elongation, or other damage, the NPRM proposed to require removing the torque tube from service. The NPRM was prompted by a report of a spiral crack in the torque tube that appears to have originated from a hole where the tail rotor torque tube control fitting attaches to the torque tube on a Model 369FF helicopter. This crack resulted in increased left pedal movement and subsequent reduced directional control pedal authority. Other model helicopters are affected due to design similarity. This condition, if not addressed, could result in failure of the torque tube, loss of tail rotor control, and subsequent loss of control of the helicopter.

FMI: www.regulations.gov