On December 1, 2001, a Bell 47G (registration N5226) was involved in an aviation accident near Ardmore, OK. Investigators recorded the probable cause as: 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. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a demonstration autorotation, a helicopter touched down on soft sod, slid, and nosed over. The tail was severed by the rotor blades before the helicopter came to rest upright.
Incident Details
A training helicopter equipped for autorotation practice experienced a nose-over event after touching down on a soft, grassy area. The flight instructor was demonstrating a full touchdown autorotation to conclude the training session, following three power recovery autorotations performed by the student pilot. The helicopter came to rest upright after rotating approximately 270 degrees to the left.
Sequence of Events
The flight instructor initiated the autorotation at 1,500 feet above mean sea level (msl) and 60 knots, aiming for the midfield median of the airport. After reducing airspeed to 40 knots, the instructor began a flare to slow the helicopter to 15–20 knots. At 10 feet above ground level (agl), the collective was pulled to cushion the landing. The helicopter touched down on the soft grassy area and slid for approximately 10 feet before beginning to nose over. "The tail of the helicopter pitched upward into the blades, severing it." The helicopter then rotated left and came to rest upright.
Instructor Statement
The flight instructor reported 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."