Background
The flight was part of Exercise Highland Pursuit 2/97 conducted by No. 173 Surveillance Squadron, 1st Aviation Regiment, operating a de Havilland Canada DHC-6 (Twin Otter) aircraft. The exercise aimed to provide training for three No. 173 Squadron pilots in tropical mountainous operations in Papua New Guinea (PNG). All trainees were qualified on the aircraft type. The training pilot, who was the pilot in command, had extensive experience flying Twin Otter and other aircraft in PNG, including military service with the DHC-4 Caribou. Passengers were not carried.
Flight Plan and Departure
On 9 November 1997, the plan was to fly from Madang and return via a number of airstrips for landing and take-off exercises. A flight plan was submitted to Madang Flight Service. At 0915 PNG time, the aircraft arrived at Koinambe, where each trainee conducted landing and take-off practice. The training pilot occupied the right cockpit seat while trainees flew from the left seat. The crew had planned to track direct from Koinambe to Simbai but, before departing, assessed that this was not possible due to haze and cloud on track. The training pilot suggested following the Jimi River north-west and then a tributary towards Simbai. The navigating pilot proposed a shorter route: from about 17 km north-west of Koinambe, follow a valley extending north-east off the Jimi River. The training pilot agreed. During this discussion, no reference was made to the elevation of the Bismarck Range. The crew used an Operational Navigation Chart (ONC) at 1:1,000,000 scale.
En-Route and Loss of Position Awareness
After departing Koinambe, the crew followed the Jimi River at about 1,000 ft above ground level (AGL). The training pilot vacated the right seat for a trainee, who became the flying pilot for the sector. The navigating pilot made radio calls to report departure. Shortly after, the navigating pilot became unsure of the aircraft's position. The flying pilot conducted several left orbits while the navigating pilot obtained a Global Positioning System (GPS) fix and plotted it on the chart. The training pilot, in the cabin with a headset, agreed with the identified position. The flying pilot resumed tracking along the river.
Accident Sequence
The navigating pilot indicated a valley he believed led towards Simbai, and the flying pilot turned into it, estimating 500 ft above the treetops. No heading check was conducted. When well into the valley, the training pilot heard the flying and navigating pilots discussing the flight with unease. He moved forward and saw the aircraft at an excessive nose-high pitch angle, unable to outclimb the terrain or turn. The cockpit crew set engine controls to full power, maximum RPM, and selected 10 degrees flap. The training pilot ensured the trainee in the cabin was strapped in and positioned himself on the floor aft of the cabin bulkhead. The stall warning activated, and the aircraft crashed through trees to the ground.
Search and Location
When the crew had not reported by 1004, communication checks were initiated. An uncertainty phase was declared at 1023, upgraded to a distress phase at 1045 after a helicopter pilot reported the aircraft was not at Simbai. The helicopter pilot tracked from Simbai to Koinambe and, at 1127, received a strong emergency locator transmitter signal. The accident site was located in a valley about 9 km south of Simbai.