Robinson Helicopter Company R44 II N915BW accident near Los Angeles, California

Probable cause

The pilot’s loss of helicopter control following a precautionary landing, which resulted in a dynamic rollover.

NTSB analysis

During the flight, the pilot reported observing the main rotor gearbox chip warning light illuminate. In accordance with the helicopter's operating handbook, he performed an immediate precautionary landing. As he approached his intended landing spot, adjacent to a park trail, he saw people on the ground, so he diverted to a small clearing on a pinnacle at the end of another trail. After landing on the pinnacle and before he had a chance to fully lower the collective control, he felt the helicopter slip. He then raised the collective control, and the helicopter immediately spun to the right and rolled over. Ground scars and airframe damage indicated that, as the pilot attempted to reposition the helicopter, it most likely experienced a dynamic rollover due to the left landing skid becoming lodged against a ridge. Postaccident examination of the airframe and drive train revealed no preimpact malfunctions or failures that would have precluded normal operation. Examination of the main rotor gearbox and its associated chip detector did not reveal the presence of any debris or particles that could have triggered the detector and no anomalies that would have precluded normal operation. However, the gearbox case was breached during the accident sequence, which liberated most of the oil and possibly any chips that might have been in the gearbox; therefore, it could not be determined what triggered the detector.

Text from the NTSB. Open the NTSB docket for WPR13FA264 for the full record.