What happened
A crew was performing high altitude flight tests intended to support the acquisition of two Supplemental Type Certificates. During the maneuvers, the pilot initiated an intentional autorotation from an altitude of 200 feet while at a gross weight of 8,000 pounds. The maneuver began at 42 knots, with a one-second delay occurring before the pilot lowered the collective control.
As the helicopter approached the runway at 40 knots, the pilot was unable to arrest the rate of descent. The aircraft subsequently impacted the runway and was destroyed.
The investigation
A video camera had been utilized to record the flight testing procedures. Upon review of the recorded footage, investigators found that during at least two previous autorotations performed during the same session, the tail boom stinger had struck the ground first.
Findings
An FAA helicopter operations inspector determined that the flight parameters were outside the low end of the height-velocity curve. This condition indicated that there was either insufficient airspeed for the altitude being used, or insufficient altitude for the airspeed being used.