Summary
This document proposes superseding an existing airworthiness directive (AD) for Eurocopter Canada Ltd. Model BO 105 LS A-3 helicopters. That AD currently requires establishing a life limit for certain tension-torsion (TT) straps. This action would require reducing the "number of flights'' life limit and providing a time-in-service (TIS) life limit for those TT straps. This proposal is prompted by a recalculation by the manufacturer and subsequent changes to the service information related to the retirement time of the TT strap initially adopted as a result of an accident in which a main rotor blade (blade) separated from a Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 helicopter due to fatigue failure of a TT strap. The same part-numbered TT strap is used on Model BO 105 LS A-3 helicopters. The actions specified by the proposed AD are intended to prevent fatigue failure of a TT strap, loss of a blade, and subsequent loss of control of the helicopter.