Incident Details
A mechanic replaced one of the helicopter's lateral cyclic servos. Subsequently, the pilot conducted a test flight with the mechanic onboard. After a successful test flight, the mechanic exited the helicopter, and the pilot prepared to reposition the helicopter to the hospital helipad.
Accident Sequence
When the pilot raised the collective, the helicopter lifted approximately 2 to 4 feet above the ground and then began to roll left. The pilot attempted to correct for the left roll, but the helicopter did not respond, and the main rotor blades struck the ground.
Examination Findings
Post-accident examination revealed control continuity and that the hydraulic servos were installed correctly. No preimpact failure of the airframe was observed. Examination of the servos showed that two of the units tested to manufacturer's parameters. However, the master servo unit failed the bench test, had the appearance that it had been worked on, and did not meet manufacturer's specifications. The helicopter manufacturer stated that the condition of the master servo would not induce a 'hard over.'