What happened
On 5 February 2013, a De Havilland DHC 6-300 (registration PK-YRF) was operating a VFR cargo charter flight from Sentani International Airport to Apalapsili Aerodrome in Papua, Indonesia. The flight crew, consisting of two pilots and one engineer, approached runway 15 with the intention of observing runway conditions upon arrival.
Upon touchdown at approximately 0058 UTC, the aircraft began to skid to the left during the landing roll. In an attempt to regain control and center the aircraft, the pilot applied the right rudder, brakes, and engaged the right engine's reverse thrust. However, these actions failed to stabilize the aircraft, which continued to drift leftward. The aircraft eventually exited the runway at approximately 500 meters from the threshold, where the nose and left main landing gear became trapped in a drainage line. While there were no injuries, the aircraft sustained substantial damage.
The investigation
The investigation focused on the aerodrome conditions, the aircraft's alignment during approach, and the pilot's recovery maneuvers. Investigators noted that the runway surface at Apalapsili consisted of a clay and sandy base with grass, which becomes notably slippery following rain. The pilot in command had not flown to this specific aerodrome in two years.
Analysis of the cockpit voice recorder revealed a discrepancy in perception between the crew; while the pilot in command believed the aircraft was centered, the second in command noted the aircraft was slightly left of the centerline. Furthermore, the investigation compared the pilot's recovery actions against the Aircraft Operation Manual (AOM). The AOM specifies that to correct a skid on a slippery surface, pilots should release brakes and reduce reverse thrust to regain directional control, whereas the pilot in this instance applied brakes and reverse thrust, which worsened the skid.
Findings
- The pilot in command had not operated at Apalapsili Aerodrome for over two years.
- There was an unresolved discrepancy between the pilots regarding the aircraft's position on the runway centerline during final approach.
- The aircraft was not properly aligned with the runway bearing at the moment of touchdown.
- The pilot's recovery technique contradicted the procedures outlined in the AOM, specifically regarding the use of braking and reverse thrust during a skid.
- The runway surface was slippery due to recent weather conditions.
Safety action
Following the incident, PT. Trigana Air Service implemented several measures, including a temporary suspension of operations to Apalapsili Aerodrome for risk assessment and the issuance of safety notices regarding weather data accuracy and runway conditions. The NTSC issued recommendations for the Directorate General of Civil Aviation to provide updated safety information for light aircraft aerodromes and urged the operator to implement procedures for managing flights to aerodromes that have not been visited for extended periods.