Bell 206 L4 N73AW accident near Dewey, Arizona

Probable cause

A total loss of engine power due to the failure of the No. 2 bearing, which resulted from a fractured separator.

NTSB analysis

The commercial pilot was conducting a cross-country ferry flight. He reported that the engine chip detector caution light briefly illuminated while the helicopter was in cruise flight about 750 ft above ground level. The pilot chose to make a precautionary landing and initiated a descent. During the descent, the detector light illuminated again, followed shortly thereafter by a "loud bang" and the engine losing power. The pilot initiated an autorotation emergency landing. During the landing sequence, the main rotor blades struck the tailboom.

Examination of the engine revealed that the No. 2 bearing separator had fractured through both rails at the forward and aft sides of the bearing. The ball bearings were retained in the separator; however, half of them exhibited damage consistent with smearing and material transfer between the raceway and balls, which resulted in the failure of the No. 2 bearing and the subsequent engine power loss.

Text from the NTSB. Open the NTSB docket for WPR15LA177 for the full record.