Incident on July 27, 1983
On July 27, 1983, a Hiller FH-1180 helicopter was on a flight to certify new rotor blades. During the flight, the helicopter was accelerated to 90 mph, followed by a pull-up and deceleration to 80 mph. A pushover maneuver was then initiated. The helicopter reportedly rolled sharply to the right, pitched nose down, and yawed to the right. Recovery was made using left cyclic; however, directional control was lost before recovery, and mild mast bumping occurred.
Accident on July 28, 1983
The following day, July 28, 1983, a standard production Hiller FH-1100, registration N450FH, was flown to explore the same phenomenon. After two pushover maneuvers of increasing severity in which control was retained, the pilot attempted a repetition of the previous day's maneuver. Witnesses observed the helicopter roll and yaw to the right and pitch down as it began to break up, followed by a fire and crash. Examination revealed that the main rotor blades separated after mast bumping and mast failure occurred. There was evidence that the pilot might not have been current in teetering rotor systems and recovery from low G rolls.