Incident Details
A helicopter training flight ended in a rollover after the instructor pilot took control during a go-around. The instructor reported that he and a private pilot under instruction had performed a normal takeoff and departure. After a short flight, they arrived at Rocky Point, located 9 miles north of Ogden-Hinckly Airport, to practice pinnacle approaches and landings.
Flight Sequence
The pair reconnoitered the area at 300 feet above ground level (agl) in preparation for landing. They conducted 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 from 350 feet agl. The approach became slightly steep and extended beyond the intended landing point. The student reported a descent rate of 500 feet per minute at 25 knots. At 30 feet agl, the descent rate increased, prompting the student to abort the approach and initiate a go-around.
The instructor realized that rotor revolutions-per-minute had degraded below the normal range and took control from the student. Because the go-around had commenced, the helicopter was moving forward slowly over a descending hill slope. The instructor was unable to land the helicopter. He attempted to gain power by lowering and raising the collective, but the helicopter's skid contacted the ground and the helicopter rolled over.
Reference to Vortex Ring State
FAA-H-8083-21, the Rotorcraft Flying Handbook, states that vortex ring state (settling with power) is likely when the rate of descent exceeds 300 feet per minute and the horizontal velocity is slower than effective translational lift.