Runway excursion Accident de Havilland Canada DHC-6 Vista Liner 300 P2-ASM,

ASN Wikibase Occurrence # 319076

Date:	Tuesday 1 December 2020
Time:	09:13
Type:	de Havilland Canada DHC-6 Vista Liner 300
Owner/operator:	Air Sanga
Registration:	P2-ASM
MSN:	389
Year of manufacture:	1973
Total airframe hrs:	48082 hours
Cycles:	83877 flights
Engine model:	Pratt & Whitney Canada PT6A-27
Fatalities:	Fatalities: 0 / Occupants: 9
Aircraft damage:	Substantial
Category:	Accident
Location:	Wobagen Airstrip - Papua New Guinea
Phase:	Take off
Nature:	Passenger - Scheduled
Departure airport:	Wobagen Airstrip
Destination airport:	Bak Airstrip (AYBB)
Investigating agency:	AIC PNG
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
A de Havilland Canada DHC-6 suffered an airstrip excursion during takeoff from Wobagen Airstrip, Papua New Guinea.
That morning, the crew had flown to Wobagen on a passenger and cargo charter flight, landing at 08:47. Once on ground, the crew took passengers on board the aircraft and loaded cargo, to conduct a VFR charter flight to Bak Airstrip, located 3.8 nm north-east of Wobagen.

At about 09:13, upon reaching the threshold of strip 12, the captain, who was Pilot Flying, conducted a 180° turn and applied maximum power, transitioning from taxi into take-off roll.
The crew stated that after applying maximum power, the aircraft had a tendency to veer to the right. The captain tried to maintain the aircraft on centreline by using asymmetric thrust, however, as the aircraft accelerated down the strip, the tendency to veer right increased. About 154m down the strip, the aircraft began veering towards the right and tracked away from the centreline. As the aircraft passed the strip boundary (cone markers), with a recorded groundspeed of 40kt the crew aborted the take-off; power to idle and applied full brakes. The aircraft continued forward and veering right. Four seconds later, the aircraft impacted a drain.
The nosewheel subsequently separated from the fork causing the nose to drop and the nose gear subsequently collapsed. The momentum of the aircraft caused it to continue another 8m with the nose dragging across the ground before it impacted the right edge drain.

Wobagen Airstrip is a 600 m long airstrip (12/30) with a slope of 8° to the southeast. Landings are only permitted on runway 30, takeoffs only on runway 12.

Contributing Factors:
The crew did not action the appropriate take-off checklist which caused them to miss crucial checks and actions. This caused the engine abnormalities to go unnoticed after take-off power was applied. The abnormal parameters engine parameters remained unnoticed until impact.
The parameters of right engine indicate that it was performing at considerably lower power than the left engine, which was operating to the manufacturers specifications. The power difference between the right and left engine created the tendency of the aircraft to veer right.
The right engine T5 Turbine temperature exceeded the limit which shows that the overtemperature condition was sustained by the right engine. The wet deteriorated clay/silt surface did not allow aircrafts tires to gain sufficient traction to follow the control inputs of the PIC as he attempted to steer the aircraft back towards the centreline. As the aircraft accelerated towards the right, it ran over undulated surface. The aircraft continued veering right because the power was not reduced, and the asymmetric effect
continued. With the asymmetric thrust, the undulated slippery surface, the aircraft swerved right. This prompted the PIC to pull power into idle and apply full brakes. After pulling power to idle, and applying full brakes, the aircraft continued with momentum over the significantly slippery surface and impacted the drainage ditch at the edge.

Accident investigation: