What happened
An MD-81 arrived at Stockholm from Zurich and remained parked overnight at gate 2. During the night, temperatures fluctuated between +1°C and 0°C, resulting in the formation of clear ice on the upper surfaces of the wings. This ice was not identified by ground personnel during inspections. Following refueling, the aircraft underwent de-icing using 850 liters of Type I fluid, though the mechanic did not re-verify the upper wing surfaces for remaining ice.
The aircraft departed for Copenhagen at 08:47. Approximately 25 seconds into the climb, at an altitude of 1,124 feet, the aircraft experienced vibrations and bangs caused by a surge in the number 2 engine. While the crew attempted to adjust the throttle, the Automatic Thrust Restoration (ATR) system increased the throttle setting, which intensified the surging. Shortly after, the number 1 engine also experienced a surge, which went unnoticed by the crew. At 76 and 78 seconds into the flight, both engines failed due to the structural breakup of the stage 1 stators caused by high loads from the surges.
As the aircraft climbed through 3,206 feet, a fire warning for the number 1 engine prompted the crew to activate the fire extinguishing system. During a gliding left turn, a passenger from another airline attempted to assist the crew in the cockpit. While descending through clouds, the crew extended the flaps. The aircraft eventually descended through 980 feet and targeted a field for an emergency landing. Upon contact with trees at 121 knots, the right wing suffered significant damage. The aircraft struck sloping ground tail-first and slid for 110 meters, resulting in the fuselage breaking into three pieces. There were 0 fatalities reported in the wreckage, though the impact was severe.
Findings
- Clear ice remained on the upper wing surfaces because it was not detected during the initial inspection or the de-icing process.
- High loads from engine surges caused the structural failure of the stage 1 stators in both engines.