What happened
On 13 February 2023, flight TK0018, a Boeing 777-300ER registered as TC-JJJ, was en route from Toronto to Istanbul when it encountered severe turbulence at FL350 north of the Langjökull glacier in Iceland. The encounter triggered an aircraft upset characterized by an extreme nose-down pitch and a rapid descent. During the approximately 80-second event, the aircraft lost nearly 8,000 feet of altitude, reaching a maximum descent rate of 17,100 feet per minute. The aircraft's airspeed exceeded its maximum operating limits, and the stick shaker activated four times.
During the turbulence, the flight crew struggled to maintain control of the aircraft's lateral and vertical path. The initial turbulence caused the autopilot to disconnect. A significant conflict occurred between the flight crew members: the First Officer applied forward pressure on the control column while the Captain applied rearward pressure. This opposing force was so great that the control columns momentarily broke out from each other on two separate occasions. Additionally, the crew failed to deactivate the autothrottle, leading to a secondary struggle between the pilots' manual inputs and the automated systems. The incident resulted in seven injuries among the passengers and crew.
The investigation
The RNSA investigation examined flight data recorder (FDR) parameters, meteorological data, and crew interviews. Analysis of weather charts and satellite imagery confirmed that high-altitude mountain waves had been present over Iceland for several hours prior to the incident. While a low-level SIGMET was in effect, it did not cover the specific area of the encounter. The investigation also reviewed the crew's response to the turbulence and their management of the aircraft's automated systems during the upset.
Findings
- The primary cause of the flight upset was a loss of situational awareness and a breakdown in Crew Resource Management (CRM) during the initial encounter with severe turbulence.
- High-altitude mountain waves caused the severe turbulence and subsequent aircraft upset.
- The flight crew's reactive inputs to the turbulence exacerbated the upset condition.
- Conflicting control inputs between the Captain and First Officer led to the physical breakout of the control columns.
- The failure to deactivate the autothrottle during the upset led to a conflict between the flight crew and the automated flight systems.
- There was a lack of coordination in reviewing significant weather charts during the cruise briefing prior to entering the North Atlantic area.