Airworthiness Directives; Eurocopter Deutschland GmbH Model EC 135 Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 98-09-11 which was sent previously to all known U.S. owners and operators of Eurocopter Deutschland GmbH (Eurocopter) Model EC 135 helicopters by individual letters. This AD requires, before further flight, a review of aircraft records to determine if a tail rotor drive shaft vibration survey and installation of a Fenestron Shaft Retrofit Kit have been accomplished; before further flight, and thereafter at intervals not to exceed 15 hours time-in-service, inspecting the tail rotor drive shaft bearing (bearing) attaching lock plates for bent-open tabs, and broken or missing slippage marks; and visually inspecting each bearing support for cracks. This amendment is prompted by three reports of loose bearings and attachment bolts, and one report of a cracked bearing support. Excessive vibrations in the tail rotor drive shaft can loosen attachment bolts or cause cracking in the bearing supports. This condition, if not corrected, could result in loss of drive to the tail rotor and subsequent loss of control of the helicopter.