Airworthiness Directives; Eurocopter Deutschland GmbH (ECD) Model MBB-BK 117 A-1, A-3, A-4, B-1, B-2, and C-1 Helicopters

This amendment adopts a new airworthiness directive (AD), applicable to Eurocopter Deutschland GmbH (ECD) (Eurocopter) Model MBB- BK 117 A-1, A-3, A-4, B-1, B-2, and C-1 helicopters, that requires initial and repetitive inspections of the main rotor (M/R) blade upper and lower surfaces for bulging. This amendment is prompted by two reported incidents in which a balance weight became detached from inside the M/R blade structure and migrated toward the tip of the M/R blade. The actions specified by this AD are intended to detect movement of a balance weight and to prevent severe vibrations and a subsequent precautionary landing.