LAX83FA362

On 7/27/83, mild mast bumping occurred during a pushover maneuver while a hiller FH-1180 was on a flt to certify new rotor blades. Prior to the incident, the helicopter was accelerated to 90 mph. This was followed by a pull-up & deceleration to 80 mph, then the pushover was initiated. The helicopter reportedly rolled sharply to the right & pitchednose down with some yaw to the right. Recovery was made with left cyclic; however, directional control was lost before recovery & mild mast bumping. On 7/28/83, FH-1100, N450FH, a standard production model, was flown to explore the phenomenon. After 2 pushovers with increasing severity, in which control was retained, the plt attempted a repetition of the previous day's maneuver. Witnesses observerved the helicopter roll & yaw to the right & pitch down as it began to break up, then burn & crash. An exam revealed the main rotor blades separated after mast bumping & mast failure occurred. There was evidence the plt might not have been current in teetering rotor systems & recovery from low g rolls.