Eurocopter AS350B3 N172AE accident near Blaine, Washington

Probable cause

The pilot's failure to maintain main rotor rpm, which resulted in a hard landing. Contributing to the accident were the flight instructor's delayed remedial action and inadequate supervision of the flight.

NTSB analysis

During an annual helicopter proficiency evaluation flight, the flight instructor told the commercial pilot to conduct manual governor operations and the flight instructor then positioned the governor switch from "auto" to "man" while on the downwind leg to the runway. After performing a left 360-degree turn, the commercial pilot initiated a normal approach to the runway with the intention of performing a run-on landing. The commercial pilot stated that as the helicopter descended through 20 feet above ground level (agl), he attempted to increase throttle and collective to arrest the rate of descent when it "felt like the bottom fell out" and the helicopter landed hard on the asphalt runway surface in a slight nose high attitude. The flight instructor reported that he heard the aural low rotor RPM horn sound and noticed the rotor RPM was slowing through 350 rpm as the helicopter was descending through about 20 feet agl. The instructor stated that before he could react to correct the situation the helicopter struck the ground. Examination of the helicopter by a Federal Aviation Administration inspector revealed that the tail boom was partially bent and one of the main rotor blades was damaged. No preimpact mechanical anomalies with the helicopter were reported by either pilot.

Text from the NTSB. Open the NTSB docket for WPR09TA001 for the full record.