Airworthiness Directives; Eurocopter Deutschland GmbH (ECD) (Eurocopter) Model MBB-BK117 A-1, A-3, A-4, B-1, B-2, and C-1 Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Eurocopter Model MBB-BK117 A-1, A-3, A-4, B-1, B-2, and C-1 helicopters, that currently requires initial and repetitive inspections of both surfaces of the tail boom vertical fin (vertical fin) spar, the skin, and the left-hand and right-hand frame sheets for cracks or loose rivets. This amendment requires the same initial and repetitive inspections of the vertical fin spar that are required by the existing AD, and also requires repairing certain cracks, if found, and repairing and reporting loose rivets and certain other cracks, if found. This amendment is prompted by an accident which occurred on April 15, 1997, resulting in one fatality. A subsequent investigation revealed that the vertical fin had failed as a result of a fatigue crack that initiated on the left side of the vertical fin spar cap. The actions specified by this AD are intended to prevent failure of the vertical fin and subsequent loss of control of the helicopter.