Incident Overview
On 5 February 2013, a De Havilland DHC 6-300 Twin Otter, registration PK-YRF, operated by PT. Trigana Air Service as a charter cargo flight, experienced a runway excursion upon landing at Apalapsili aerodrome in Papua, Indonesia. The flight departed from Sentani International Airport at 0010 UTC under Visual Flight Rules. On board were two pilots and one engineer. No injuries occurred, but the aircraft sustained substantial damage.
Flight Details
The Pilot in Command (PIC) had not flown to Apalapsili for two years. Prior to departure, he gathered aerodrome information and received weather reports indicating clear conditions over Apalapsili. The aircraft climbed to 8,000 feet on radial 220 of the JPA VOR. Approximately 25 nautical miles from Apalapsili, the crew began descending to 6,000 feet, planning to use Runway 15. They flew overhead at 4,500 feet and joined a left downwind for Runway 15. A normal approach was executed with a VREF speed of 70 knots.
Landing and Skid
At 0058 UTC, the aircraft touched down on Runway 15. During the landing roll, the aircraft skidded to the left. The PIC applied right rudder pedal, brake, engaged right engine reverse, and turned the nose wheel steering to the right in an attempt to recover alignment. The aircraft came to a stop on the left side of the runway, approximately 500 meters from the runway threshold. The nose wheel and left main wheel became trapped in a drainage line.
Runway Marks and Conditions
Wheel marks on the runway indicated that the touchdown was not aligned with the runway centerline, and the aircraft consistently moved left, with marks not parallel to the runway bearing. The nose wheel mark was closer to the right wheel mark near the end of the roll, indicating the aircraft was facing to the right (skidding) while moving left. The runway surface at Apalapsili consisted of clay and sand base with grass; it was smooth and generally hard but could become soft and rutted during rain. The surface was slippery after rain the previous night. The aerodrome had no ground-based navigation aids or ground-to-air radio communication.
Contributing Factors
The investigation identified three contributing factors: (1) the pilot flying had not been qualified to the aerodrome; (2) the approach was not aligned with the runway centerline; and (3) the recovery technique (cornering technique) applied by the pilot was not appropriate with the technique as per the Aircraft Operating Manual.