Accident Overview
A night cargo flight operated by a single pilot crashed into the ocean while conducting a visual approach between two islands. The aircraft was on a routine cargo flight and had been in contact with air traffic control. At 0501 hours, the controller advised the pilot to maintain 6,000 feet when the aircraft was 11 miles from the destination airport. Two minutes later, the flight was cleared for a visual approach to follow a preceding Boeing 737 and was instructed to switch to the airport's common traffic advisory frequency. The destination airport had a control tower, but it was closed overnight.
Flight Path and Descent
Radar-derived flight path data indicated that the pilot altered the course to the west, most likely to maintain spacing from the preceding aircraft, and then descended into the water as he began a turn back toward the airport. The majority of the wreckage sank in 4,800 feet of water and was not recovered, preventing examination and testing of cockpit instruments. A performance study showed that the aircraft's airspeed, pitch, rates of descent, and bank angles during the approach were within expected normal ranges. The pilot did not make any transmissions indicating problems. Another cargo flight crew that landed just before the accident and an airport employee reported that the pilot transmitted that he was landing on the active runway and was 7 miles from landing.
Last Radar Contact
Radar data showed that when the aircraft was 6.5 miles from the airport, the last recorded radar return indicated a mode C altitude of minus 100 feet mean sea level. The pilot most likely descended into the ocean due to spatial disorientation. Visual meteorological conditions prevailed, but there was no natural horizon and few external visual references available during the approach. This increased the importance of monitoring flight instruments to maintain awareness of the aircraft's attitude and altitude. However, the pilot's tasks during the approach included maintaining visual separation from the airplane ahead and lining up with the destination runway, requiring visual attention outside the cockpit. These competing tasks probably created shifting visual frames of reference, left the pilot vulnerable to common visual and vestibular illusions, and reduced his awareness of the aircraft's attitude, altitude, and trajectory.
Probable Cause
The official probable cause is the pilot's spatial disorientation and loss of situational awareness. Contributing to the accident were the dark night and the task requirements of simultaneously monitoring the cockpit instruments and the other airplane.