Hughes OH-6A N6641D accident near Benson, Arizona

Probable cause

The pilot under instruction's inadequate autorotation technique and the instructor pilot’s delayed remedial action to arrest the rate of descent of the helicopter while in an autorotation flare.

NTSB analysis

The instructor pilot reported that they were practicing autorotations to the runway. During a straight-in autorotation at approximately 200 feet above ground level, the instructor called for an increase in throttle to bring rotor rpm into the normal operating range in preparation for landing. Between 200 feet and 100 feet agl, the instructor assisted the flying pilot with the throttle increase when he realized that the pilot had delayed throttle application. The flying pilot then initiated the flare at approximately 50 feet agl. The flying pilot leveled the helicopter and applied collective to slow the descent rate. Upon realizing that the descent rate had not been checked prior to beginning the flare, the instructor joined the flying pilot on the controls. The helicopter landed hard on the runway and bounced, rotated to the left of runway heading as it touched down a second time, resulting in the collapse of the right landing skid. The pilot reported that were no mechanical anomalies with the flight control systems.

Text from the NTSB. Open the NTSB docket for WPR09TA277 for the full record.