What happened
On 17 January 2013, a Pilatus Porter PC-6/B2-H4, registration PK-UCJ, was operating a non-scheduled cargo flight from Sentani to Wamena, Papua. The flight crew consisted of an instructor acting as Pilot in Command and a trainee acting as Pilot Flying.
Upon landing on runway 15 at Wamena Airport, the aircraft touched down on the centerline. However, the runway surface was slippery due to water and rubber deposits following recent rain. As the pilot flying applied reverse thrust, the aircraft began to veer toward the right. In an attempt to correct the deviation, the pilot applied left rudder and left braking, but this failed to stabilize the aircraft. As the aircraft moved toward the edge of the runway, the instructor took control and advanced the power to increase rudder effectiveness. Despite these efforts, the aircraft exited the runway at approximately 157 meters from the initial touchdown, striking a taxiway marking. The impact caused the left aileron, left wing tip, and horizontal stabilizer to detach. The aircraft briefly became airborne before re-entering the runway and taxiing to the apron. There were no injuries to the two crew members, though the aircraft sustained major damage.
The investigation
The investigation examined the aircraft's flight path, the runway conditions, and the crew's response to the loss of control. Because the aircraft lacked flight data and cockpit voice recorders, investigators utilized aerodynamic theory and assumptions to reconstruct the event. The inquiry focused on the interaction between reverse thrust, braking, and the slippery runway surface, as well as the effectiveness of the crew's decision-making during the critical landing phase.
Findings
- The runway surface was contaminated with water and rubber, significantly reducing friction.
- The crew had not conducted an approach and landing briefing that specifically addressed the risks of using reverse thrust on a wet runway.
- The pilot flying's attempt to recover the skid using left rudder and left braking actually reduced the tires' ability to maintain directional control by increasing lateral forces on the slippery surface.
- The instructor's decision to take control occurred at a moment when the speed and space were insufficient to effectively counteract the existing side forces.
Safety action
The operator, YAJASI, has since expanded its approach briefings to include surface and wind conditions, planned brake usage, and swerve recovery procedures. Additionally, the operator has implemented swerve recovery training into its proficiency checks and reviewed control exchange procedures. The investigation also highlighted the need for regular runway decontamination at regional airports.