Airworthiness Directives; Airbus Helicopters Deutschland GmbH Helicopters

We propose to adopt a new airworthiness directive (AD) for Airbus Helicopters Deutschland GmbH (Airbus Helicopters) Model MBB-BK 117 A-1, MBB-BK 117A-3, MBB-BK 117 A-4, MBB-BK 117 B-1, MBB-BK 117 B-2, MBB-BK 117 C-1, and MBB-BK 117 C-2 helicopters. This proposed AD would require repetitive inspections of the tail rotor (T/R) gearbox housing. This proposed AD is prompted by a report that a crack was found in a T/ R gearbox housing. The actions of this proposed AD are intended to address an unsafe condition on these products.