What happened
On 23 January 2023, a DHC-6-300 Twin Otter, registration PK-SMS, was performing an unscheduled cargo and passenger flight from Timika to Beoga, Papua. The flight, operated by PT Semuwa Aviasi Mandiri, was conducted under Visual Flight Rules (VFR) in daylight conditions. The aircraft was carrying two pilots, an engineer, and eleven passengers.
During the approach to Beoga Airstrip, the pilot in command (PIC) reduced engine power to manage separation from two other aircraft in the area. As the aircraft descended toward the final approach, the vertical descent rate increased significantly, reaching 1,20 and the airspeed dropped to approximately 74 knots. This high-sink rate triggered the aircraft's stall warning.
The aircraft touched down on Runway 16 approximately 240 meters from the threshold. Upon landing, the aircraft veered to the right. Despite the pilot's attempts to regain directional control using left rudder and asymmetric engine power, the aircraft continued off the runway onto the shoulder. During the excursion, the right wing struck trees, causing substantial damage to the wingtip and leading edge. The aircraft eventually came to a stop on the right shoulder. All occupants evacuated the aircraft safely, and no injuries were reported.
The investigation
The KNKT investigation focused on the flight sequence, aircraft condition, and cockpit recording functionality. Investigators found that the aircraft was within its weight and balance limits and possessed valid airworthiness and registration certificates.
A significant technical finding involved the Cockpit Voice Recorder (CVR). While the CVR was functional, it had failed to record the flight in question or several preceding flights. This failure was attributed to the activation of an inertial switch, likely triggered by a hard landing during a previous flight that had not been reported or reset. The investigation also noted that the aircraft sustained damage to the propeller blades and the right wing structure due to the impact with vegetation.
Findings
- The aircraft experienced a high vertical descent rate of 1,200 feet per minute during the final approach, leading to a stall warning.
- The aircraft veered right upon touchdown, resulting in a runway excursion and contact with trees.
- The CVR failed to capture the occurrence due to an unaddressed inertial switch activation following a previous hard landing.
- The pilot did not report the previous hard landing event to the operator, which prevented the necessary reset of the recording system.
Safety action
Following the incident, the operator issued a safety notice to reinforce pilot ground training, emphasize Crew Resource Management (CRM), and improve adherence to standard operating procedures. The KNKT has specifically recommended that the operator ensure all significant handling events, such as hard landings, are reported to the company in a timely manner to ensure flight equipment, such as the CVR, remains operational.