With two pilots and six passengers, a Viking DHC-6-300, was to operate a charter flight, under Visual Flight Rules, from Wobagen Airstrip to Bak Airstrip (both in Sandaun Province, Papua New Guinea). It would be the second flight of the day for this crew.
The aircraft in its final position (Source: https://twinotterworld.com © Unknown)
On their arrival at the Wobagen Airstrip, the pilots observed the grass runway and the parking area to be wet. To avoid having to stop to complete the ‘before take-off checklist’ the crew elected to complete this checklist while parked. This procedure (completing the before-take-off checklist) was developed by the experienced pilots for take-offs on slippery and muddy airstrips.
At 09:11 local time, the crew called the Moresby Flight Information Service. They informed them that their destination for this flight would be the Bak Airstrip, this instead of their initial destination, Kiunga (as previously planned). As planned the ‘before take-off checklist’ was completed at the parking area and the aircraft was taxied towards the take-off end of airstrip 11.
The Pilot In Command (PIC) was the pilot flying for the flight, when they arrived at the beginning of the airstrip he started a left turn to line op with the centreline, this was done by means of the tiller and asymmetric thrust. During the turn, power was added to both engines. As they came on the centreline a little correction to the right was made after which the throttles were moved forward for the take-off, and the aircraft started to accelerate down the strip.
The aircraft in its final position (Source: https://twinotterworld.com © Unknown)
When the aircraft reached a speed of approximately 33 knots it started to deviate to the righthand side of the airstrip. The PIC attempted to correct the deviation using asymmetric thrust, however this was not successful. Approximately 200 meters into the take-off roll, at a speed of 42 knots the deviation became so great that the PIC decided to abort the take-off by bringing the throttles to idle and applying full wheel brakes. The aircraft had now started sliding sideways, in the direction of its momentum forward past and ran into a soft patchy undulated surface. The aircraft subsequently impacted a drainage ditch along the southwestern edge of the airstrip. After coming to a stop the crew shut the engines down, the passengers opened the cabin door and evacuated the aircraft through that door. The cockpit crew evacuated the aircraft via their respective cockpit doors. One of the passengers received minor injuries.
Damage to the aircraft was substantial, however repairable.
The take-off path (Source & © PNG AIC)
The runway excursion was investigated by the Accident Investigation Commission of Papua New Guinea (PNG AIC). On the 13th of May 2022, the PNG AIC published their final report pursuant to ICAO Annex 13. Several findings were recorded, among others;
An unapproved take-off procedure was used for the take-off and did not follow the OEM-approved AFM normal take-off procedures.
The take-off procedure used by the Operator does not cater for certain actions and/or considerations from the approved Manufacturers AFM.
The crew did not identify or recognize the right engine parameter abnormalities during the take-off. (The T5 Turbine temperature exceeded the limit which shows that the overtemperature condition was sustained by the right engine)
The engine parameters for the right engine indicate that the right engine was operating abnormally (below specifications).
The PNG AIC report on the accident, which served as the source for this blog, can be accessed by clicking on the .pdf file below. It contains detailed data on the investigation.
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