Pilot error is being blamed for two fatal air crashes in Hawaii last year that killed four people.

A National Transportation Safety Board investigation into the June 17 crash of an air tour plane on the rugged slopes of Mauna Loa found that Island Hoppers pilot Katsuhiro Takahashi, 40, deviated from his planned flight route and flew into mountainous terrain amid cloudy conditions.

The single-engine, four-seat Cessna 172M slammed into a heavily forested area at the 4,500-foot elevation of the mountain near Pahala. The wreckage was not located until June 22.

Also killed in the crash were Nobuhiro Suzuki, 53, and his wife, Masako Suzuki, 56, of Chiba, Japan.

A separate NTSB report on the Jan. 14, 2008, crash of an Alpine Air cargo plane into the ocean 11 miles southwest of Lihue Airport found that pilot Paul Akita, 37, likely experienced "spatial disorientation" during the night flight and may have been distracted by cockpit duties that included monitoring an Aloha Airlines Boeing 737 jet flying ahead of him.

Radar tracking of the Hawker Beechcraft 1900C's flight path indicated the pilot altered his flight course to the west, most likely for spacing from the jet, and descended into the water as he began a turn back toward the airport, the report said.

The majority of the plane wreckage sank in 4,800 feet of water and was not recovered, so examinations and testing of the engine and other systems could not be performed. The report noted that although the skies were clear, no natural horizon and few external visual references were available during the pilot's visual approach.