Accident Overview
An hour after landing in an open field at 6,200 feet mean sea level near Parkman, Wyoming, within the Bighorn National Forest, a pilot conducted a practice takeoff without a passenger to assess the helicopter's performance. The helicopter achieved effective translational lift and hovered normally, then climbed out at 40 knots.
Sequence of Events
Shortly after clearing a 75-foot ridge located 100 to 150 yards from the takeoff field, the aircraft exited ground effect and encountered a downdraft. Subsequently, the helicopter began to lose altitude. The power required for climbing exceeded the power available. The aircraft descended through 60 to 80 feet of trees before impacting the ground and coming to rest inverted.
Pilot and Performance Data
The pilot reported no mechanical problems and stated the engine was running upon impact. The density altitude at the time of the accident was calculated to be 7,578 feet. Based on calculated weight and performance data, the helicopter's gross weight at departure was approximately 1,232 lbs. At an indicated airspeed of 35 knots, the maximum obstacle clearance height was 75 feet, with a maximum distance of 800 feet.