A Turkish Airlines Boeing 777-300ER flying from Toronto experienced a sudden and steep altitude loss of nearly 8,000 feet during a severe turbulence encounter due to a pilot error over Iceland on February 13, 2023. The incident occurred as the aircraft was cruising at 35,000 feet. According to the Icelandic Transportation Safety Board (RNSA), the descent happened rapidly, reaching rates of up to 17,100 feet per minute.
According to FlightGlobal, the situation unfolded when the crew, surprised by the turbulence, responded with sharp and conflicting control inputs. Both pilots engaged their control columns at the same time, each making opposite and abrupt movements. The crew also adjusted engine thrust aggressively, only to be counteracted by the autothrottle system.
The aircraft, in response to the inputs and turbulence, entered an overspeed state. It reached 368 knots, which is 18 knots over its maximum operating speed, and climbed to Mach 0.92. The stick-shaker activated several times, warning of a possible stall, as the aircraft’s descent intensified.
Mixed actions and delayed coordination
Flight data shows that the pilots deployed speedbrakes to slow the aircraft, but possibly forgot to retract them. With speedbrakes extended and thrust briefly reduced to idle, the aircraft began to descend. During this time, the autothrottle attempted to restore engine power.
The situation worsened when the first officer pushed the control column forward in response to a stick-shaker warning, which caused the autopilot to disengage. The jet pitched nose-down and descended at 1,360 feet per minute. The captain then added a nose-up input, but he did not announce that he was taking control. This caused confusion as both pilots were handling the controls without coordination.
The RNSA noted, “Both pilots were simultaneously acting as pilot flying, while neither pilot was monitoring the flight, suggesting a breakdown of crew resource management.” The flight’s data recorder indicated that opposing forces were applied to the controls, peaking at around 440 newtons (100 pounds) each. This led to multiple breakouts of the control columns, in which the system averaged out their inputs.
The aircraft’s descent continued and it reached a steep 18.3° nose-down attitude with a descent rate over 9,000 feet per minute. It exceeded maximum operating speed again just below 30,700 feet. Only as the rate reached nearly 17,100 feet per minute did the captain apply a stronger pull, and the pitch angle began to increase.
As the aircraft approached 27,500 feet, opposing inputs from the pilots neutralized each other, reducing pitch to zero. The airspeed also dropped, stopping the overspeed warnings. After that, the aircraft began to climb again. The crew re-engaged the autopilot and retracted the speedbrakes.
Missed warnings and post-event actions
Reykjavik air traffic control attempted to contact the crew several times during the descent but received no response until the aircraft had recovered. One of the pilots finally replied, sounding “out of breath,” and stated that the flight had experienced severe turbulence.
Once the flight stabilized, the Boeing 777 climbed back to 31,500 feet, where it encountered more turbulence. The crew then descended to 28,000 feet. When conditions improved, the commanding captain returned to the cockpit and resumed control of the flight. The crew also received a SIGMET warning for the area and accepted rerouting from air traffic control.
During the turbulence event, five cabin crew members and two passengers sustained minor injuries. Investigators noted that the seatbelt signs had been switched on 10 minutes before the encounter due to earlier light turbulence.
Although satellite data showed signs of high-altitude mountain waves over Iceland before the event, there were no meteorological warnings in place at the time. The cockpit voice recorder was unavailable for review as it had been overwritten. The recording system stores only two hours of data, and the crew did not secure it in time. They had discussed diverting to either Glasgow or Copenhagen but chose to continue to Istanbul, where medical support was requested upon arrival.
The RNSA also noted that the flight was operating with two captains and a first officer undergoing line training. The first officer, who had only 38 hours on the 777, was flying the aircraft when the turbulence began. At that time, the captain was not in the cockpit and was taking a rest break.
