Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to Eurocopter Deutschland GmbH (ECD) Model EC-135 helicopters. The existing AD requires conducting a tail rotor drive shaft vibration survey (survey), installing a Fenestron Shaft Retrofit Kit, inspecting each tail rotor drive shaft bearing (bearing) attaching lock plate for bent-open tabs and broken or missing slippage marks, and visually inspecting each bearing support for cracks. This action would require conducting the survey and installing the Fenestron Shaft Retrofit Kit. This AD would also require installing double bearing supports and struts, revising the required compliance time for the repetitive inspections of the bearing attach hardware and supports, and removing the requirement to contact the FAA if a lock plate tab is bent open or if slippage marks are broken or missing. This proposal is prompted by continued reports of misaligned or cracked bearing supports and loose bearing attachment bolts. The actions specified by the proposed AD are intended to prevent loss of drive to the tail rotor and subsequent loss of control of the helicopter.