Robinson R44 N3038W accident near La Belle, Florida

Probable cause

The loss of main rotor rpm due to the failure of one or more of the drive belts for undetermined reasons.

NTSB analysis

The pilot reported that he was conducting a flight at a low altitude and speed when he heard a light tapping sound followed by the low rotor rpm warning horn. He attempted to simultaneously initiate an autorotation and maintain forward speed to reach a clearing. The tail boom and tail rotor struck trees, and the pilot lost directional control of the helicopter. The helicopter touched down in the clearing, spun about 180 degrees to the right, and rolled onto its left side. A postaccident examination revealed that one of the rotor drive belts was separated and that each of the remaining three belts was frayed and partially displaced from at least one of its respective sheaves. According to a representative for the helicopter manufacturer, the fraying was typical of a drive belt that was displaced from the sheave while the engine was running. The fraying could be caused by the belt being too loose, by abrupt maneuvering of the helicopter, or by the helicopter striking the ground when the engine was running. The representative also stated that when a drive belt starts to fail, it tends to make a repetitive noise similar to that reported by the pilot, and that drive belt failure could result in low rotor rpm. The reason(s) for the drive belt failures could not be determined and maintenance records were not available during the investigation.

Text from the NTSB. Open the NTSB docket for ERA10LA019 for the full record.