What happened
On 7 November 2003, a De Havilland DHC-6 Twin Otter, registration VP-FBB, was returning to Rothera Airfield in the British Antarctic Territory after a flight from Fossil Bluff. During the landing sequence, the pilot encountered challenging wind conditions caused by local topography. After an initial unsuccessful landing attempt due to turbulence, the pilot opted for a second approach using Runway 18.
Upon touchdown approximately 200 metres from the threshold, the pilot applied braking and rudder inputs to maintain the aircraft's path. However, as the aircraft progressed down the runway, it began to veer significantly to the left. In an attempt to correct the deviation, the pilot utilized nosewheel steering. The aircraft's trajectory became increasingly unstable, leading to the detachment of the nosewheel. The aircraft then tipped onto its right wing and performed a forward somersault, coming to rest inverted approximately 520 metres from the runway threshold. The two occupants, including one minor, escaped the wreckage with only minor injuries.
The investigation
Investigators examined the runway surface and ground marks, which indicated that the aircraft began veering about 300 metres from the threshold. The marks showed that the left mainwheel was carrying very little weight and that the nosewheel was traveling sideways, with the nose ski contacting the surface just before the gear failed. The investigation also looked into the pilot's recent flying history and the specific aerodynamic configuration of the aircraft during the landing.
Findings
Several contributing factors were identified in the loss of control:
- The pilot's decision to use a flap setting beyond 20 degrees reduced aileron effectiveness and delayed the aircraft's weight from settling onto the wheels.
- To prepare for a potential go-around, the pilot used little to no reverse thrust, which resulted in a longer landing roll and slower deceleration.
- The extended landing roll moved the aircraft into a zone where the wind direction and strength changed abruptly.
- The pilot's recent flying experience had been on a different aircraft type, and a lack of recent currency on the Twin Otter was noted.
- The use of nosewheel steering was inappropriate at the speed of the aircraft, as the flight manual cautions against its use until taxi speeds are reached.
- The runway surface was softer than usual due to a recent thaw, which allowed the landing gear to dig into the ground.
The failure to use full reverse thrust to decelerate the aircraft quickly was identified as a primary factor in the accident.