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

This amendment supersedes an existing airworthiness directive (AD), applicable to The Enstrom Helicopter Corporation (Enstrom) Model F-28, F-28A, F-28C, F-28C-2, F-28F, 280, 280C, 280F, and 280FX 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 existing AD also requires replacement of the clutch assembly at certain time-in-service intervals. This amendment requires the same inspections and replacements as required by the existing AD, but would provide for installation of an additional approved replacement part number and provide a reference to three additional manufacturer service documents. This amendment is prompted by the approval of an additional replacement clutch assembly; the manufacturer's issuance of additional service information, and the need to correct a service information letter's number. The actions specified by this 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.