Flight History
On 1 June 2007, a de Havilland DHC-6-300 Twin Otter operated by Trigana Air Service, registration PK-YRU, was conducting a take-off from Mulia Airstrip in Papua, Indonesia. The aircraft was on a training flight, with the handling pilot undergoing captaincy training under the supervision of an instructor pilot. During the early acceleration phase of the take-off roll, the aircraft began veering to the right. The pilots continued the take-off, but directional control was lost. The aircraft departed the runway and struck a ditch and rocks on the right shoulder of the runway. Witnesses observed the aircraft turning right, then left, and back to the right before leaving the runway. Main-wheel tire marks extending more than 65 meters indicated heavy braking on the left brake.
Injuries and Damage
The aircraft was substantially damaged. None of the occupants—the instructor pilot, the pilot under training, and any other persons on board—were injured.
Personnel Information
The instructor pilot held the position of Pilot in Command for the flight and was supervising the captaincy training of the other pilot. The pilot under training was in the process of obtaining captaincy qualification. The investigation did not identify any medical or pathological factors that contributed to the event.
Aircraft Information
The aircraft, a de Havilland DHC-6-300 Twin Otter (registration PK-YRU), was equipped with two turboprop engines. The weight and balance were within the prescribed limits for the flight. No aircraft or system defects were found that could have contributed to the loss of directional control.
Wreckage and Impact Information
The aircraft's forward fuselage, right wing, and nose landing gear area were substantially damaged. The right main landing gear wheel was also damaged. The wreckage came to rest after impacting the ditch and rocks on the right shoulder of the runway.
Investigation Findings
The National Transportation Safety Committee (NTSC) investigated the accident. Despite analyzing the evidence, the investigation was unable to determine why the aircraft commenced veering to the right during the initial take-off roll. The pilot under training stated that he was unaware that the power levers were still in the full position and that he did not immediately respond to the instructor's shout to avoid using the steering handle. The investigation considered the possibility that the nose-wheel steering was not centered before the take-off roll and that the pilot under training may have unknowingly held an inappropriate nose-wheel steering position. No technical defects were found that could explain the loss of directional control.