Bell OH-58A N158TR accident near Brawley, California

Probable cause

A total loss of engine power due to the failure of the No. 8 bearing and the subsequent failure of the scavenge oil pump.

NTSB analysis

The pilot was conducting agricultural operations at night and had just departed from a company loading area. About 150 ft above ground level (agl), the pilot experienced a sudden power surge, abnormal engine noise, and vibration. The pilot believed that engine failure was imminent and turned back toward his point of departure. Engine power decayed, and the pilot bled off rotor rpm to maneuver over terrain toward flat ground. The helicopter landed hard, entered a pylon whirl condition, and the main rotor hub assembly separated from the main rotor mast.

Postaccident examination of the airframe revealed no evidence of preaccident mechanical malfunction or failure. However, postaccident examination revealed a sheen of oil beneath the engine and that the engine’s compressor (N1) and power turbine (N2) systems were seized. Further examination of the engine revealed multiple failed bearings, failed drives, and fractures within the turbine scavenge oil pump assembly. The engine had been installed on the helicopter about 10 flight hours before the accident.

Based on metallurgical analysis of the engine components, the No. 8 bearing likely failed and shed debris to the oil pump, which bound the first level oil pump gears and led a gear tooth to fracture and the pump driveshaft to fail. Subsequently, the engine was starved of oil and lost all power. The cause of the bearing failure could not be determined.

Text from the NTSB. Open the NTSB docket for WPR24LA041 for the full record.