The National Transportation Safety Board was unable to uncover the reason why a single-engine Cessna flew into a Haleakala mountainside three miles southwest of Hana Airport on Dec. 15, 2005, killing the pilot.

A final report released this week said the weather was clear and that there was no turbulence at the time the plane crashed at the 2,300-foot elevation. Investigators who examined the aircraft wreckage found no evidence of mechanical malfunctions, the safety board said.

Alan Gerow, 58, of Salt Lake City, had rented the Cessna 172S from Maui Aviators at Kahului Airport and was planning to fly to Hana and return to Kahului later in the day, the NTSB report said. Gerow held a commercial pilot certificate and was authorized to fly single- and multi-engine airplanes.

A certified flight instructor at Kahului Airport had checked him out in the aircraft three weeks before the crash, the NTSB report said.

After taking off from Kahului, the pilot incorrectly made a left turn, and after some confusion got back on course toward Hana, the report said. No one saw the plane crash.

A helicopter pilot involved in a miconia-spraying operation spotted the burning wreckage and notified authorities. The engine and cockpit area were buried 6 feet into the ground, and the helicopter pilot told the NTSB that based on the position of the wreckage, the direction of flight was not consistent with a normal approach or departure from Hana Airport and would have ensured the plane's impact with the terrain.