What happened
On the night of April 6, 2014, a SAS Boeing 737-600, registration LN-RRY, was performing a commercial landing at Ängelholm airport in Sweden. The flight, arriving from Stockholm/Arlanda, was conducting an automated ILS approach to runway 14 under instrument conditions. At an altitude of approximately 200 feet, the First Officer, acting as the pilot flying, disconnected the autopilot.
During the final stages of the approach, the aircraft began to drift toward the left side of the runway. While the crew could see the runway edge lights, the wet surface and darkness made it difficult to discern the runway markings or the pavement itself. As the aircraft crossed the threshold, it was positioned roughly ten meters to the right of the centerline and began traveling diagonally toward the left edge. The Captain intervened to assist with maneuvering, attempting to bring the aircraft back toward the center. However, during the touchdown, the left main gear struck two runway edge light fixtures. There were no injuries to the 36 passengers or 5 crew members, and the aircraft sustained no damage.
The investigation
The Swedish Accident Investigation Authority (SHK) examined flight data from the Quick Access Recorder (QAR) and interviewed the flight crew. The investigation focused on the transition from instrument flight to visual references and the environmental conditions at the time of the incident. Investigators analyzed the wind conditions, which included a crosswind from the right, and the visibility, which was approximately 1,300 meters in moderate drizzle with a low cloud base.
Findings
- The aircraft's drift was influenced by the fact that the aircraft's crab angle was not reduced in proportion to the decreasing crosswind strength.
- The crew likely experienced a Black-hole approach illusion, a perceptual error where the lack of visual references—such as the inability to see runway markings—makes it difficult to detect lateral drift in a timely manner.
- The transition from instrument flight to visual references was compromised by the lack of distinct visual cues on the wet runway.
Safety action
Following the incident, the operator indicated that they would review training manuals regarding flare and touchdown procedures. The airline also considered revising operational manuals concerning illusions, disorientation, and misperceptions, and planned to present the findings to flight instructors to improve simulator training for similar conditions.