Flight History
On 13 February 2023, a Boeing 777-300ER (registration TC-JJJ) operating as Turkish Airlines flight TK0018 from Toronto (CYYZ) to Istanbul (LTFM) encountered severe turbulence north of the Langjökull glacier, Iceland. The aircraft, carrying 280 persons, was cruising at FL350 when the upset occurred. The flight crew comprised three pilots; the Captain (Pilot Monitoring) and First Officer (Pilot Flying) were on the flight deck, while the Commander was resting. The turbulence, caused by high-altitude mountain waves, resulted in an upset condition with extreme pitch angles and a high rate of descent. The aircraft lost approximately 8,000 feet of altitude in one minute, reaching a maximum descent rate of 17,100 feet per minute, and briefly descended to FL273. Airspeed exceeded limits, and multiple stick shaker activations occurred.
Crew Response and Control Issues
The autopilot and autothrottle were engaged before the turbulence. Large control column inputs disengaged the autopilot. Subsequently, the pilots exerted opposite forces on their control columns—the First Officer pushed forward while the Captain pulled back—causing the columns to break out from each other. Without deactivating the autothrottle, the pilots and the autothrottle competed for control. The upset lasted approximately 80 seconds.
Weather Information
Satellite and weather data indicated that high-altitude mountain waves had existed over Iceland for hours before the incident. No SIGMET warning for severe mountain waves was in effect prior to the encounter. Four minutes after the upset, SIGMET M01 was issued but did not cover the incident area. About 40 minutes later, SIGMET M02 expanded the warning area to include severe mountain waves.
Injuries and Damage
Seven persons (two passengers and five crew members) sustained injuries. The aircraft sustained minor damage to interior parts.
Cause
The investigation determined that the incident was caused by a loss of situational awareness and a breakdown in crew resource management in response to the initial turbulence encounter.