What happened
On 15 September 2021, a DHC-6-300 Twin Otter, registered PK-OTW, was performing an unscheduled cargo flight from Nabire to Bilorai in Papua, Indonesia. The flight was operated by a crew consisting of two pilots and one engineer.
While approaching Bilorai Airport, the crew monitored weather reports from preceding aircraft. After observing that other traffic had landed using Runway 27, the crew decided to attempt a landing on the same runway. However, during the approach, the aircraft encountered clouds. A stall warning was recorded, prompting the crew to initiate a go-around maneuver.
During the subsequent left turn to reposition for a landing on Runway 09, the aircraft descended into mountainous terrain. The aircraft struck a ridge at an elevation of approximately 8,10 and was destroyed. There were 3 fatalities among the crew members.
The investigation
The KNKT investigation examined the flight trajectory using flight following data and reviewed cockpit voice recorder (CVR) audio. The investigation focused on the aircraft's compliance with Visual Flight Rules (VFR) and the effectiveness of the onboard Terrain Awareness and Warning System (TAWS).
Investigators noted that while the aircraft was equipped with a Sandel ST3400 TAWS, the CVR did not record any aural alerts from the system during the descent. Additionally, the investigation reviewed the operator's manual and the specific go-around procedures documented for Bilorai Airport compared to the actual maneuvers performed by the crew.