Schweizer 300C N1510A accident near Ogden, Utah

Probable cause

The pilot under instruction's encounter with a settling with power condition, and the flight instructor's failure to maintain adequate rotor rpm during the subsequent go-around. Also causal was the instructor pilot's delayed remedial action during the approach sequence and his inadequate supervision of the flight.

NTSB analysis

The instructor pilot and the private pilot under instruction arrived at the location where they were going to practice pinnacle approaches and landings. They reconnoitered the area at 300 feet above ground level (agl) in preparation for landing. They performed a power check at 500 feet agl, and concluded that engine power was sufficient to maintain an out of ground effect hover. The student began the approach at 350 feet agl. The helicopter's rate of descent was 500 feet per minute (fpm) at 25 knots of airspeed. Settling with power (vortex ring state) can be encountered when rates of descent are greater than 300 feet per minute and airspeed below that of translational lift. The helicopter began to overshoot the point of intended landing, and the approach became almost vertical. At 30 feet agl, the helicopter's descent rate increased and the student aborted the approach and began a go-around. The instructor realized that rotor revolutions-per-minute (rpm) had degraded below the normal range, so he took the control of the helicopter. Because the go-around had been initiated, the helicopter was moving forward slowly over a descending slope and the instructor was not able to land the helicopter. He attempted to gain power by lowering and raising collective; however, the helicopter's skid contacted the ground and the helicopter rolled over.

Text from the NTSB. Open the NTSB docket for LAX08CA138 for the full record.