What happened
On 15 October 2019, a scheduled passenger flight operated by a Boeing 737-8AS, registration EI-EMA, was descending toward Malta-Luqa (LMML) from Birmingham. While maneuvering to avoid identified cumulonimbus clouds, the aircraft encountered a period of intense atmospheric instability.
Prior to the encounter, the pilot had observed significant weather on the radar and proactively instructed the cabin crew to secure the cabin early. The fasten seat belt sign was active, and passengers were seated. However, as the aircraft descended through approximately 18,000 feet, it experienced a sudden and severe upset. At the time of the turbulence, three cabin crew members were positioned at the rear of the aircraft securing galley equipment and lavatories. The force of the movement caused all three crew members to be thrown to the floor, resulting in one serious injury to a crew member who suffered fractures to both bones in the lower left leg.
The investigation
The investigation analyzed flight data monitoring (FDM) records provided by the operator. The data confirmed that the aircraft was performing various heading changes to navigate around weather cells. As the aircraft passed through 16,500 feet, the speed brake was stowed, and immediately following this, turbulence intensified.
Flight data recorded a momentary vertical acceleration of 2.02 g. This spike in acceleration coincided with a rapid drop in the Static Air Temperature (SAT), indicating the aircraft had entered a highly unstable atmospheric layer. For approximately 26 seconds, the aircraft experienced continuous vertical accelerations of +/- 1.3 g. The autopilot remained engaged throughout the duration of the turbulence encounter.
Findings
- The pilot was aware of the high probability of turbulence due to visual observations and radar detection of cumulonimbus clouds.
- The flight crew had taken preemptive measures to mitigate risk by reducing speed, limiting bank angles, and notifying the cabin crew to secure the cabin.
- The sudden and severe aircraft upset occurred while the crew were in the process of securing the rear galley.
- The rapid fluctuations in Static Air Temperature (SAT) confirmed the presence of highly variable and unstable local atmospheric conditions.