Incident
An MBB BK 117 helicopter, which had been exported from Canada, was undergoing reassembly and modification from model A-3 to A-4. To expedite the modification for use as an air ambulance, a 24-hour/day schedule was employed. During maintenance on vertical control tubes, a shift change occurred. After completion, the helicopter was flown on a test flight.
Flight and Sequence of Events
No anomalies of the flight controls were noted until the pilot was flaring to hover before landing. The pilot reported that while power was being applied, the cyclic and pedals were manipulated accordingly. A left movement of the cyclic was required to overcome a roll and drift to the right. At that time, the pilot noted insufficient cyclic control, and the helicopter continued to roll to the right until the main rotor blades struck the ground. The helicopter then impacted on its right side and slid to a stop.
Investigation Findings
An investigation revealed that the lateral and collective upper adjustable control rods had been interchanged, and the color coding had been repainted. The interchange of control rods resulted in a misrigged swashplate with a higher preset collective pitch and a right tilt of the swashplate.
Probable Cause
The interchange of control rods resulting in a misrigged swashplate with a higher preset collective pitch and a right tilt of the swashplate.