Summary
This document proposes the adoption of a new airworthiness directive (AD) applicable to Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 A-1, A-3, A-4, B-1, B-2, and C-1 helicopters. This proposal would require modifying the engine and transmission cowling doors (cowling doors). This proposal is prompted by an emergency landing of an ECD Model MBB-BK 117 helicopter after the No. 1 engine cowling opened, separated from the helicopter, and struck the main and tail rotor blades resulting in a tail rotor imbalance and subsequent departure of the tail rotor gear box from the helicopter. The actions specified by the proposed AD are intended to prevent the cowling doors opening during flight, separating from the helicopter and impacting the main or tail rotor blades, and subsequent loss of control of the helicopter.