Enstrom F 28C N5697B accident near Ontario, California

Probable cause

The student pilot's mismanagement of the main rotor rpm, which resulted in low rotor rpm, a high descent rate, and a subsequent hard landing.

NTSB analysis

The solo student pilot reported that he entered the downwind leg to set up for the helicopter's first landing of the day. When abeam the touchdown location, he conducted the prelanding checks with no anomalies noted. Before turning onto the base leg, the pilot lowered the collective, reduced the throttle, and started to descend about 100 ft per minute. During the descent, he observed that the engine rpm was slightly above 2,900 rpm. He reduced the throttle, and the rpm reduced slightly; however, it again increased to 2,900 rpm, and the manifold pressure was about 10 inches of mercury. When the helicopter was about 400 ft above ground level, the pilot heard the engine sound increase, and he observed that the engine rpm had increased to between about 3,300 and 3,500 rpm. The helicopter was unable to reach the runway, so the pilot continued to descend it toward a pasture, and it landed hard in the dirt.

A postaccident airframe and engine examination and subsequent engine run revealed no preimpact anomalies that would have precluded normal operation. The observed damage to the main rotor blades was consistent with blade coning, a condition indicative of low main rotor rpm. It is likely that the student pilot mismanaged the main rotor rpm during the descent, which resulted in a low rotor rpm and a high descent rate during landing.

Text from the NTSB. Open the NTSB docket for WPR17LA158 for the full record.