What happened
On the evening of 24 November 2011, a SAAB 340B, registration SE-KXJ, was performing a scheduled commercial flight from Hemavan Tärnaby Airport to Vilhelmuina. The takeoff occurred in darkness and challenging winter weather, characterized by heavy snow showers and gusting winds.
As the aircraft accelerated down the runway, a sudden increase in wind and a heavy snow shower moved over the airfield. During the takeoff roll, the aircraft began to drift toward the left edge of the runway. At approximately 800 meters into the roll, the left main wheel and nose wheel left the paved surface and entered a snow bank. The pilot attempted to abort the takeoff using thrust reversal and braking, but the aircraft continued to travel parallel to the runway for about 350 meters. During this sequence, the right engine failed after slush was ingested into the air intake. The aircraft then veered sharply to the left, completely departing the runway and coming to a stop near the runway edge. There were no injuries to the 11 persons on board.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the flight data recorder, cockpit voice recorder, and the aircraft's mechanical systems. The investigation focused on the impact of the weather conditions on the crew's ability to maintain directional control. Investigators also reviewed the aircraft's maintenance history and the crew's preparations, noting that the aircraft was airworthy and the crew had followed standard procedures. The investigation specifically looked into the possibility of mechanical failure in the rudder system, but no malfunctions were found.
Findings
- The takeoff was performed in demanding winter conditions involving darkness and visibility reductions due to snow.
- The aircraft's left gear made contact with a snow bank, which prevented effective directional correction despite rudder input.
- The loss of the right engine was caused by slush entering the engine intake during the excursion.
- A perceptual illusion caused by large, blowing snowflakes and the glare from illuminated landing lights led the pilots to fail to notice the aircraft's lateral drift in time.
Safety action
Following the incident, the operator updated its manual to include specific guidance regarding takeoff illusions associated with blowing snow, addressing a previous gap where such information was only documented for landing procedures.