Primary finding
Probable cause
the flight instructor's selection of an unsuitable area for practicing a full touchdown autorotation, which resulted in a nose over. A contributing factor was the soft ground.
Investigator assessment
Analysis narrative
The student pilot had completed three power recovery autorotations to the south, and the flight instructor was to demonstrate a "full touchdown autorotation" to end the training session. The flight instructor initiated the autorotation at 1,500 feet msl and 60 knots to the airport's mid-field median. After slowing to 40 knots, the instructor began a flare to reduce the airspeed to 15-20 knots. At 10 feet agl, he pulled collective to cushion the landing. The helicopter touched down on the soft grassy area and slid for approximately 10 feet before starting to nose over. "The tail of the helicopter pitched upward into the blades, severing it." The helicopter rotated left approximately 270 degrees before coming to rest upright. The flight instructor stated that "weather had saturated the ground and caused the sod to be soft on the usual landing area. It was not visible from the helicopter."
Source record
Factual narrative
On December 1, 2001, at 1030 central standard time, a Bell 47G helicopter, N5226, was substantially damaged during a practice autorotational landing at the Ardmore Downtown Executive Airport near Ardmore, Oklahoma. The helicopter was registered to a private individual and operated by Versatile Helicopters, Inc., dba Versatile Aviation of Ardmore, Oklahoma. The flight instructor and the private pilot rated student were not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 instructional flight. The local flight originated from the Ardmore Downtown Executive Airport, approximately one hour prior to the accident. The student pilot had completed three power recovery autorotations to the south, and the flight instructor was to demonstrate "a full touchdown autorotation" to end the training session. The flight instructor initiated the autorotation at 1,500 feet msl and 60 knots to the mid-field median. After slowing to 40 knots, the instructor began a flare to reduce the airspeed to 15-20 knots. At 10 feet agl, he pulled collective to cushion the landing. The helicopter touched down on the soft grassy area and slid for approximately 10 feet before starting to nose over. "The tail of the helicopter pitched upward into the blades, severing it." The helicopter rotated left approximately 270 degrees before coming to rest upright. The flight instructor stated that "weather had saturated the ground and caused the sod to be soft on the usual landing area. It was not visible from the helicopter."