Airworthiness Directives; The Enstrom Helicopter Corporation Model F-28, F-28A, F-28C, F-28C-2, F-28F, 280, 280C, 280F, and 280FX Series Helicopters

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This document proposes the supersedure of an existing airworthiness directive (AD), applicable to The Enstrom Helicopter Corporation Model F-28, F-28A, F-28C, F-28C-2, F-28F, 280, 280C, 280F, and 280FX series helicopters, that currently requires initial and repetitive inspections of a certain main rotor transmission clutch assembly (clutch assembly) for bearing roughness, noise, lock-up, or improper oil level and, if necessary, replacement of the clutch assembly. The current AD also requires replacement of the clutch assembly at certain time-in-service intervals. This action would require the same inspections and replacements as required by the current AD, but would provide an additional approved replacement part number and provide a reference to three additional manufacturer service documents. The actions specified by the proposed AD are intended to prevent failure of the clutch assembly, loss of control of the main rotor system, and subsequent loss of control of the helicopter.