Primary finding
Probable cause
The loss of torque due to a failure of a transmission drivebelt and the pilot's delayed landing flare during the autorotation. Contributing to the accident was the dusk light condition and the corn crop.
Investigator assessment
Analysis narrative
The helicopter pilot reported that during the local area flight he heard "loud noises" behind the cockpit that were followed by a loss of torque to the rotor system. He immediately initiated an autorotation into a cornfield. The tailboom stinger contacted the ground during the landing flare, which pushed the tailboom up into the path of the main rotor system. The helicopter then landed hard and rolled over onto its right side. The pilot reported that the accident could have been prevented if he had initiated his flare about two feet higher, but at the time he was unsure of his altitude above the ground due to the corn crop and the dusk light condition. A postaccident inspection of the helicopter revealed that one of the transmission drive belts had failed and another belt had separated from its pulley assembly.
Source record
Factual narrative
The helicopter pilot reported that during the local area flight he heard "loud noises" behind the cockpit which was followed by a loss of torque to the rotor system. He immediately initiated an autorotation into a cornfield. The tailboom stinger contacted the ground during the landing flare, which pushed the tailboom up into the path of the main rotor system. The helicopter then landed hard and rolled over onto its right side. The pilot reported that the accident could have been prevented if he had initiated his flare about two feet higher, but at the time he was unsure of his altitude above the ground due to the corn crop and the dusk light condition. A post-accident inspection of the helicopter revealed that one of the transmission drive belts had failed and another belt had separated from its pulley assembly.