Summary
The FAA proposes to adopt a new airworthiness directive (AD) for all Airbus Helicopters Deutschland GmbH (AHD) Model MBB-BK117 A-1, MBB-BK117 A-3, MBB-BK117 A-4, MBB-BK117 B-1, MBB-BK117 B-2, MBB-BK117 C-1, MBB-BK117 C-2, and MBB-BK117 D-2 helicopters. This proposed AD was prompted by the FAA's determination that aging of the elastomeric material of certain tension torsion straps (TT-Straps), during the period since manufacturing date up to first flight on a helicopter, may affect its structural characteristics. This proposed AD would require the replacement of certain TT-Straps, implementation of storage life limits for TT-Straps, a prohibition on installing certain TT-Straps and conditions for installation of certain other TT-Straps, as specified in a European Union Aviation Safety Agency (EASA) AD, which is proposed for incorporation by reference (IBR). The FAA is proposing this AD to address the unsafe condition on these products.