Incident Overview
On October 16, 2009, at 1045 Pacific daylight time, a McDonnell Douglas Helicopter 500N (registration N521HB) operated by the Huntington Beach Police Department experienced a main rotor strike on its tail boom during a practice autorotation landing. The accident occurred at Los Alamitos Army Airfield in Los Alamitos, California. The flight was conducted as a public-use training flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed. The helicopter had departed from the Huntington Beach Police Department helicopter pad at 0945.
Sequence of Events
According to the certified flight instructor (CFI), he and the pilot under instruction were practicing emergency procedures, specifically power recovery autorotations. The CFI reported that at approximately 700 feet above ground level (agl), he rolled the throttle to idle and entered the autorotation. At about 50 feet agl, he rolled the throttle on late, realized the ground was approaching rapidly, and decided to execute a running landing.
The pilot under instruction stated that he inadvertently applied partial throttle, which prevented the engine from regaining full power. With the throttle positioned at approximately 25 percent, the rotor rpm decayed. As the helicopter contacted the ground, a rotor blade struck the tail boom.
Damage and Injuries
The helicopter sustained substantial damage to the tail boom. The certified flight instructor and the pilot under instruction were not injured. After the accident, the pilot shut down the helicopter and confirmed the damage.
Mechanical Condition
The pilot reported that the helicopter and engine experienced no mechanical failures or malfunctions during the flight.