Oceania

The cause of this accident was a loss of control of the aircraft, and although the evidence available does not permit the reason for the loss of control to be determined, the possibility can not be eliminated that the pilot suffered an impairment of ability and, coincidentally, was deprived temporarily of aileron control.

The probable cause of the accident was that the means of securing the oil metering unit to the No. 2 cabin blower became ineffective and this led to the initiation of a fire within the blower, which propagated to the w$ng fuel tank and substantially reduced the strength of the main spar upper boom. It is probable that the separation of the oil metering unit arose from an out-of-balance condition induced by rotor break-up but the source of the rotor break-up could not be determined.
The following findings were reported:
- The crash of the aircraft followed the failure in an upward direction of the port wing between No. 1 and No. 2 engines at approximately 1302:30 hours Eastern Standard Time when the aircraft was at a height of 3 500 ft to 4 000 ft above ground level,
- The port wing failed as a result of a weakening of the main spar due to a fire in No. 2 cell of No. 2 fuel tank,
- The fire originated in the No. 2 cabin blower and travelled through the rear of No. 2 engine nacelle and port wheel bay to the fuel tank,
- The fire in No. 2 cabin blower was initiated as a result of a rotor break-up, the blower subsequently being driven in an out-of-balance condition by the quill shaft long enough for the metering unit to become separated from the rear end cover by the resulting vibration,
- The metering unit continued to be driven after separation and lubricating oil continued to be supplied. The driven rotor lost its rear stub shaft radial location and caused metal-to-metal contact which generated a temperature sufficiently high to ignite the oil in that area,
- It is not possible on the evidence to determine what was the cause of the rotor break-up.

The primary cause of this accident was,the incurrence of reverse thrust during simulated failure of No. 4 engine on take-off. That condition arose when very rapid rearward movement of the power lever (customary only on crew training flights involving simulated engine failure) generated an inertia force which caused the associated thrust brake lever to rise and enter the reverse idle detent. After lift-off, the minimum control speed essentially required to overcome the prevailing state of thrust imbalance was never attained and an uncontrollable roll, accompanied by some degree of yaw and side-slip in the same direction, ensued. When the condition of reverse thrust was recognized and eliminated,insufficient time and height were available to allow the aircraft to recover from its precarious attitude before it struck the ground.

The in-flight opening and separation from the structure of the air-stair door which struck the aircraft's tail and so damaged it that uncontrollable pitch-down of the nose resulted in the aircraft diving into the sea.

Loss of control during takeoff following the tailwheel failure.

Loss of control during takeoff due to quartering wind.

Apparently due to the lack of visibility, the crew started the descent prematurely, causing the aircraft to be too low and to struck the mountain.