2000 Australia Beechcraft King Air Crash - Investigation

Investigation

The accident was investigated by the Australian Transport Safety Bureau (ATSB), a federal body responsible for investigating transportation accidents in Australia. The final accident report was published in March 2001. The report was unable to make a definitive conclusion as to the cause of the crash.

The report found all those aboard the aircraft, including the pilot, had likely become incapacitated and begun suffering from hypoxia.

The accident report stated, "After the aircraft climbed above the assigned altitude of FL250, the speech and breathing patterns of the pilot, evidenced during the radio transmissions, displayed changes consistent with hypoxia." Investigators were, however, unable to conclusively dismiss toxic fumes as the cause. "The incapacitation of the pilot and passengers was probably due to hypobaric hypoxia because of the high cabin altitude and their not receiving supplemental oxygen" the report said, adding, "The reasons for the pilot and passengers not receiving supplemental oxygen could not be determined."

The ATSB found it likely that the autopilot was engaged, and this caused the aircraft to fly on a straight heading; the vertical path of the aircraft indicated climb power had been set before the occupants of the aircraft were incapacitated. "The design of the aircraft systems were such that, with the autopilot engaged, the engines would continue to operate and the aircraft would continue to fly without human input until it was disrupted by other events, such as collision or fuel exhaustion," according to the accident report. It was suggested that, towards to the end of the flight, the fuel tank for the left engine on the aircraft was almost empty. "The near exhaustion of fuel in the left wing tanks may have produced at least one, and probably several, momentary losses of left engine power shortly before all power was lost" the report said. "The aircraft yawed and rolled towards the left engine, as was observed shortly before the aircraft collided with the ground."

The accident report said due to the damage to the aircraft upon impact with the ground, investigators were unable to conclude if any of the eight aboard used the oxygen system. However, the report stated "The absence of a distress radio call, or an attempt to descend the aircraft, and the likelihood that the pilot did not don his oxygen mask, suggested that the pilot was unaware that the aircraft was unpressurised or depressurising." The passengers, the report added, were also likely not wearing their oxygen masks, as there was no noise recorded on the ATC transmissions indicating they were attempting to assist the pilot.

Investigators were not able to determine what caused the depressurisation of the aircraft, but stated likely causes included either an incorrect switch selection due to pilot error or a mechanical failure in the aircraft pressurisation system. The air traffic control recordings suggested it was unlikely a rapid decompression had occurred. "During an explosive or rapid depressurisation of a pressurised aircraft, however, the noise, pressure changes, temperature changes and draughts within the cabin would have alerted the occupants that a substantial failure had occurred," the report added. The document listed the two main factors in the accident as,

1. The aircraft was probably unpressurised for a significant part of its climb and cruise for undetermined reasons.
2. The pilot and passengers were incapacitated, probably due to hypobaric hypoxia, because of the high cabin altitude and their not receiving supplemental oxygen.