Event Summary
A helicopter conducting practice autorotations experienced a hard landing. The flight was intended to prepare a student for a commercial flight test the following day. After a series of maneuvers, the certified flight instructor (CFI) stopped for a break and to add fuel, then resumed practice autorotations on runway 4.
Sequence of Events
Following the break, the crew completed two 180-degree autorotations from 1,000 feet above ground level (agl). They then performed a 180-degree autorotation from 700 feet agl without incident. During a subsequent 180-degree autorotation, at about 100 feet agl and 70 knots, the CFI perceived a sudden increase in the helicopter's descent rate. The CFI called for a go-around and added throttle, but the helicopter did not respond. The helicopter contacted the runway in a level attitude, and the skids were reported to be "spread completely." Throughout the descent, the rotor rpm remained within the green arc, and the low rotor rpm horn did not activate.
Environmental Conditions
The CFI reported the wind at the airport as 040 degrees at 20 knots, gusting to 28 knots. The closest official weather reporting station, Kona airport, located 26 miles southwest of the accident site, recorded winds at 1454 as 230 degrees at 10 knots and at 1353 as 200 degrees at 12 knots. METAR observations for three hours on either side of the accident time indicated winds from the southwest at generally 10 to 15 knots. No intervening topographical features exist between Kona and the accident site, though the Waimea-Kohala airport is situated at the base of Mauna Kea mountain.
Examination Findings
No mechanical problems were identified with the helicopter prior to the accident.