Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Eurocopter Deutschland GmbH (ECD) Model MBB-BK 117 series helicopters. This proposal would require initial and repetitive inspections of the main rotor (M/R) blade upper and lower surface for bulging. This proposal 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 the proposed AD are intended to detect movement of a balance weight to prevent severe vibrations and a subsequent precautionary landing.