What happened
During a night cargo operation between two islands, a single-pilot flight was conducting a visual approach to an airport. At 0501 hours, while approximately 11 miles from the destination, air traffic control instructed the pilot to maintain an altitude of 6,000 feet. Two minutes later, the aircraft was cleared for a visual approach, following a Boeing 737, and instructed to transition to the common traffic advisory frequency. Although the destination airport featured an air traffic control tower, the facility was closed during the overnight hours.
Radar tracking indicated that the pilot adjusted the flight path westward, likely to maintain spacing from the preceding aircraft. As the pilot initiated a turn back toward the airport, the aircraft descended into the ocean. The majority of the wreckage settled in water measuring 4,800 feet deep and was not retrieved. Because the wreckage was not recovered, investigators were unable to perform physical examinations or testing on the cockpit's altitude and attitude instruments.
Despite the lack of physical evidence, a performance study confirmed that the aircraft's airspeed, pitch, bank angles, and rates of descent remained within normal parameters during the approach. The pilot made no radio transmissions indicating distress; in fact, an airport employee and a preceding cargo crew noted that the pilot had reported being 7 miles from the runway and intended to land on the active strip. However, radar data revealed that at a distance of 6.5 miles from the airport, the aircraft's mode C altitude report indicated a level of -100 feet mean sea level.
Findings
Investigators concluded that the pilot likely entered a state of spatial disorientation during the descent. Although the weather conditions were visual, the lack of a natural horizon and minimal external visual references during the night approach made the flight particularly hazardous. The pilot was required to manage competing tasks, including maintaining visual separation from the preceding Boeing 737 and aligning with the runway. These duties necessitated looking outside the cockpit, which likely caused shifting visual frames of reference and left the pilot susceptible to vestibular and visual illusions, ultimately reducing awareness of the aircraft's true altitude and trajectory.