A serious turbulence incident over Icelandic airspace caused a Turkish Airlines Boeing 777 to descend suddenly from cruising altitude. However, the French Civil Aviation Safety Investigation Authority (BEA) stated that turbulence alone could not account for the dramatic descent, suggesting more complex causes behind the event.
No Meteorological Warning, but Danger Was Present
The flight, which departed from Toronto on 13 February 2023 and was bound for Istanbul, had two captains and a second officer undergoing line training on board. Although the SIGMET meteorological warning system issued no alerts before the incident, satellite imagery and other data revealed the presence of high-altitude mountain waves over Iceland.
Inexperienced Pilot and Resting Captain
At the time of the incident, the second officer—who had only 38 hours of type rating training—was in control of the aircraft. The captain was off-duty and resting outside the cockpit. While the cockpit voice recorder was unavailable, the flight data recorder showed increasing tailwinds, rising engine power, and a drop in airflow.
Chain Reaction Triggered by Turbulence
As the airspeed increased from 281 knots to 300 knots, nearing the aircraft’s maximum Mach limit, the crew retarded the thrust levers to idle. The autothrottle attempted to compensate by increasing power again. At this point, the crew deployed the speed brakes, which were apparently left extended. This caused engine thrust to drop once more, leading to an uncontrolled descent.
Stick-Shaker Warnings and Lack of Coordination Between Pilots
A loss of speed and a sudden increase in angle of attack activated the stick-shaker system. When the second officer pushed the control column forward, the autopilot disengaged, and the aircraft entered a nose-down “porpoising” motion. Although the captain intervened, he failed to announce that he was taking control, creating a critical situation where both pilots were attempting to control the aircraft without coordinating with each other.
Descent Rate of 16,000 Feet per Minute
Simultaneous control inputs in opposite directions caused physical strain on the flight controls. At one point, the aircraft pitched down to 18.3°, and the descent rate exceeded 16,000 feet per minute. As opposing forces cancelled each other out, the pitch value returned to neutral around 27,500 feet. From that point, airspeed decreased, overspeed warnings ceased, and the jet began to climb again.
Autopilot Re-engaged, Turbulence Persisted
After the aircraft stabilised, the autopilot was re-engaged, and the speed brakes were retracted. Reykjavik Air Traffic Control attempted to contact the crew several times. Eventually, one of the pilots breathlessly reported severe turbulence. After climbing to 31,500 feet, the aircraft encountered further turbulence and descended again to 28,000 feet.
Captain Returned to Cockpit, Route Change Recommended
The captain returned to the cockpit and resumed control. Reykjavik control then issued a SIGMET for the area and recommended the flight transition into another airspace. The crew accepted the proposal.
Seven Injured, Voice Recording Overwritten Shortly After
Five cabin crew members and two passengers sustained minor injuries. The seatbelt signs had been turned on roughly ten minutes before the turbulence began. Although diversion options such as Glasgow and Copenhagen were discussed, the crew chose to proceed to Istanbul for urgent medical attention. However, this decision resulted in the cockpit voice recorder—which only stores two hours of data—overwriting the crucial audio from the time of the incident.
© AeroHaber.com / Mevlüt Zor – mevlutzorr@gmail.com
