CC138804 Twin Otter - Epilogue

Report / August 23, 2012 / Project number: CC138804-D-Cat

Location: Near Inuvik, Northwest Territories (NT)
Date: 23 August 2012
Status: Investigation Complete

While conducting austere airfield training, during the takeoff from the tundra near Horn Lake, southwest of Inuvik, NT, the Twin Otter aircraft’s nose landing gear collapsed.  There were no injuries among the four crew and two passengers.

After arriving at the austere landing site, the crew evaluated it for suitability of use.  Following several recconnaisance passes and a cautious light weight-on-wheels drag manoeuvre, the crew determined the terrain to be rough but suitable and so they conducted a full stop landing.  An inspection of the landing area then indicated that the surface was covered with water-saturated tundra hummocks between which the wheels had sunk into.  Tundra hummocks are small mounds of soil and vegetation related to the permafrost.

During the takeoff attempt, the aircraft stuck fast even with the application of full power.  The crew then shut the aircraft down, dug out the hummocks in front of each wheel and inserted plywood ramps to facilitate rolling the aircraft over their tops.  Although this proved to be effective, during the takeoff roll just as the aircraft was approaching flying speed the nose wheel sunk into soft ground, shearing the nose landing gear strut above the wheel yoke.  The nose then dropped to the ground and the aircraft skidded forward, sustaining serious damage, as the crew aborted the takeoff.

Although following procedure, the crew was unable to detect the presence of the saturated hummocks prior to landing.  The investigation’s recommendations, therefore, focussed on improving the evaluation criteria during the arial reconnaissance and drag manoeuvre.

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