Summary
We propose to adopt a new airworthiness directive (AD) for ECD Model MBB-BK 117 C-2 helicopters. This proposed AD would require inspecting the rigging of the power-boosted control system and, if there is a nonparallel gap between the rigging wedges and the inner sleeves, performing a rigging procedure. This proposed AD is prompted by the discovery, during rigging of the main rotor controls, of movement of the longitudinal main rotor actuator piston after shut-down of the external pump drive. Such movement could cause incorrect rigging results. The proposed actions are intended to prevent incorrect rigging results, which could impair freedom of movement of the upper controls and subsequent reduced control of the helicopter.