What happened
Following its exportation from Canada, a MBB BK 117 helicopter was undergoing a modification process to upgrade it from model A-3 to model A-4. To expedite the conversion for use as an air ambulance, maintenance was being performed on a 24-hour schedule. During the maintenance of the vertical control tubes, a shift change occurred.
Upon completion of the work, the helicopter was taken on a test flight. During the flight, no anomalies in the flight controls were observed until the pilot attempted to flare for a hover before landing. As power was applied, the pilot manipulated the cyclic and pedals to maintain position. To counteract a drift and roll to the right, left cyclic input was required. However, the pilot encountered insufficient cyclic control, and the aircraft continued to roll to the right. The main rotor blades struck the ground, causing the helicopter to impact on its right side and slide to a stop. There were no injuries reported.
The investigation
The investigation determined that the lateral and collective upper adjustable control rods had been interchanged during the maintenance process. Furthermore, the color coding on these components had been repainted, masking the error. This interchange of control rods resulted in a misrigged swashplate characterized by a right tilt and a higher preset collective pitch.