What happened
On 1 June 2007, a de Havilland DHC 6-300 Twin Otter, registration PK-YRU, was performing a scheduled flight sector from Mulia to Wamena in Papua, Indonesia. The flight was being conducted as a captaincy training session, with an experienced instructor pilot in the right seat and a pilot under training in the left seat.
As the aircraft accelerated down runway 27, which features a 10% downslope, it began to veer toward the right. The aircraft's path became unstable, swerving left and then back to the right. Despite the instructor's attempts to use differential braking and rudder to correct the deviation and abort the takeoff, the aircraft could not be stopped on the runway. The aircraft exited the right side of the pavement, impacting a ditch and large rocks located on the runway shoulder. The impact caused the nose landing gear to break and the radome to separate from the fuselage. The aircraft eventually came to rest facing perpendicular to the runway. There were no injuries to the two crew members or the single passenger on board.
The investigation
The investigation focused on the loss of directional control and the physical state of the runway environment. Investigators examined the wreckage and found no mechanical defects or system failures that would have contributed to the excursion. The aircraft was confirmed to be airworthy and within weight and balance limits at the time of departure.
Analysis of the cockpit environment revealed that the pilot under training was using the nose-wheel steering handle. The pilot noted that the event occurred so rapidly that he was unaware the power levers remained in the full-on position. While the investigation could not definitively prove the position of the steering lever at the moment of impact, evidence suggested the nose-wheel steering may not have been centered prior to the takeoff roll.
Findings
- The aircraft was mechanically sound and properly loaded for the flight.
- The crew members were properly licensed and qualified for the operation.
- The aircraft experienced an uncommanded veer to the right during the early stages of the takeoff roll.
- The nose-wheel steering may not have been centered before the takeoff roll commenced, leading to an inappropriate steering position.
- The runway shoulder contained hazardous obstacles, specifically a ditch and rocks, which contributed to the severity of the impact.
Safety action
- The NTSC recommended that the Directorate General of Civil Aviation review the safety of the runway shoulder at Mulia Airstrip. The recommendation emphasizes that airport operators should ensure the shoulder area is free of obstacles like ditches and rocks to mitigate risks during runway excursions.