Accident de Havilland Canada DHC-6 Twin Otter 100 C-FCCE,

Date:	Wednesday 4 February 2009
Time:	09:15
Type:	de Havilland Canada DHC-6 Twin Otter 100
Owner/operator:	Transwest Air
Registration:	C-FCCE
MSN:	8
Year of manufacture:	1966
Engine model:	Pratt & Whitney Canada PT6A-20
Fatalities:	Fatalities: 0 / Occupants: 7
Aircraft damage:	Substantial
Category:	Accident
Location:	La Ronge Airport, SK (YVC) - Canada
Phase:	Take off
Nature:	Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:	La Ronge Airport, SK (YVC/CYVC)
Destination airport:	Deschambeault Lake, SK
Investigating agency:	TSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
The Transwest Air spring ski-equipped de Havilland DHC-6-100 (registration C-FCCE) was taking off from a ski strip east of and parallel to runway 36 at La Ronge Airport, SK (YVC). After the nose ski cleared the snow, the left wing rose and the aircraft veered to the right and the captain, who was the pilot flying, continued the takeoff. The right ski, however, was still in contact with the snow. The aircraft became airborne briefly as it cleared a deep gully to the right of the runway. The aircraft remained in a steep right bank and the right wing contacted the snow-covered ground. The aircraft flew through a chain link fence and crashed into trees surrounding the airport. The five passengers and two crewmembers evacuated the aircraft with minor injuries. There was a small fire near the right engine exhaust that was immediately extinguished by the crew.

FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS:
1. Contamination on the wings of the aircraft was not fully removed before take-off. It is likely that asymmetric contamination of the wings created a lift differential and a loss of lateral control.
2. Although the operator was not authorized for short take-off and landing (STOL) take-off on this aircraft, the crew conducted a STOL take-off, which reduced the aircraft's safety margin relative to its stalling speed and minimum control speed.
3. As a result of the loss of lateral control, the slow STOL take-off speed, and the manipulation of the flaps, the aircraft did not remain airborne and veered right, colliding with obstacles beside the ski strip.

FINDINGS AS TO RISK
1. The out of phase task requirements regarding the engine vibration isolator assembly, as listed in the operator's maintenance schedule approval, results in a less than thorough inspection requirement, increasing the likelihood of fatigue cracks remaining undetected.
2. The right engine inboard and top engine mounts had pre-existing fatigue cracks, increasing the risk of catastrophic failure.

OTHER FINDINGS
1. The cockpit voice recorder (CVR) contained audio of a previous flight and was not in operation during the occurrence flight. Minimum equipment list (MEL) procedures for logbook entries and placarding were not followed.
2. The Transwest Air Limited safety management system (SMS) did not identify deviations from standard operating procedures.

Accident investigation: