Summary
This document proposes the supersedure of an existing airworthiness directive (AD) for Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 helicopters. That AD currently requires, before further flight, creating a component log card or equivalent record and determining the calendar age and number of flights on each tension- torsion (TT) strap. This action would establish a life limit for certain main rotor TT straps. This proposal is prompted by an accident in which a main rotor blade (blade) separated from an ECD Model MBB-BK 117 helicopter due to fatigue failure of a TT strap. The actions specified by this AD are intended to prevent fatigue failure of a TT strap, loss of a blade, and subsequent loss of control of the helicopter.