Summary
We propose to adopt a new airworthiness directive (AD) for Eurocopter Deutschland GmbH (Eurocopter) Model EC135 P1, EC135 P2, EC135 P2+, EC135 T1, EC135 T2, EC135 T2+, and MBB-BK 117 C-2 helicopters with a certain external mounted hoist system (hoist) with boom support assembly (boom) installed. This proposed AD would require inspecting the boom for a crack and, if a crack exists, replacing the boom with an airworthy boom. This proposed AD is prompted by cracks found on the boom during a pre-flight check of a hoist on an MBB-BK 117 C-2 helicopter. The proposed actions are intended to detect a crack and prevent failure of the boom, loss of the boom and attached loads, and subsequent loss of helicopter control.