Summary
This document withdraws a notice of proposed rulemaking (NPRM) that would have applied to all Mitsubishi Heavy Industries, Ltd. (Mitsubishi) MU-2B series airplanes. The proposed airworthiness directive (AD) would have superseded AD 88-23-01, which currently requires repetitively inspecting torque tube joints for cracks, and, if cracks are found, replacing the joints on all Mitsubishi MU-2B series airplanes. The proposed AD would have required you to replace the existing joints with new improved-design joints as terminating action for the repetitive inspections. The proposed AD was the result of a recent accident investigation that revealed that the improper reinstallation (following an AD 88-23-01 required repetitive inspection) of two cotter pins in the torque tube resulted in a disconnect in the flap drive train. Comments received on the NPRM suggest that the accident was related to human error and AD action is not necessary. We agree that the cause of the accident has been traced to human error, not to hardware failure. Therefore, we are withdrawing the NPRM.