Incident Overview
On 25 February 2015, at approximately 18:50 UTC, a Boeing 737-800 registered EI-DAC operated by Ryanair experienced severe clear air turbulence while en route at flight level 380 over Bordeaux, France. The aircraft was on a scheduled passenger flight from Reus Airport (Spain) to Charleroi Airport (Belgium). Two cabin crew members sustained serious injuries as a result of the turbulence. The flight diverted to Bordeaux, landing about 35 minutes after the event.
Flight History
According to the flight data recorder (FDR), cockpit voice recorder (CVR), and crew statements, the aircraft took off at 18:30. During climb through FL 100, standard procedures allowed cabin crew to release their seatbelts for onboard service. Shortly before reaching FL 380, the crew contacted Bordeaux air traffic control and asked if turbulence had been reported. The controller indicated no turbulence reports. At 18:48:57, upon reaching FL 380, the aircraft entered severe turbulence. The crew observed variations in pitch, roll, and speed, disengaging the autopilot and auto-thrust at 18:49:07. The stick shaker and overspeed warning activated. The crew descended to FL 360 and informed the controller. After stabilizing, they re-engaged the autopilot and auto-thrust. Upon learning that two cabin crew were injured, they diverted to Bordeaux.
Meteorological Conditions
Météo-France estimated conditions near the incident included wind from 360° at 100 kt at FL 340 and 90 kt at FL 380, clear sky above FL 300, temperatures around -58°C at FL 340 and -64°C at FL 380, and severe turbulence. Pre-flight weather information included SIGMETs for the Bordeaux FIR forecasting severe turbulence between FL 350 and 430. The crew modified their flight plan due to a shear rate of 12 kt/1,000 ft, flying approximately 3 NM west of the SIGMET area. However, the turbulence occurred about 15 NM from the forecast air mass.
Recorded Data
From 18:48:57 for 12 seconds, recorded parameters showed vertical accelerations between -0.38 g and +1.52 g, pitch variations from +8.4° to -2.5°, angle of attack from -9° to +10°, bank up to 19°, and indicated airspeed between 217 kt and 256 kt.
Contributing Factors
The investigation identified that the crew’s flight path modification, absence of turbulence during climb, and controller’s report of no pilot reports may have led to an underestimation of the risk. Consequently, cabin crew were authorized to start and continue service until encountering severe turbulence near a SIGMET-identified risk zone.
Safety Lessons
This event highlights the difficulty in accurately predicting clear air turbulence zones. Boundaries of risk areas in SIGMETs should be considered imprecise. When operational constraints bring an aircraft close to such an area, crews should take precautions to prevent injuries. Pilot reports are encouraged, but absence of reports does not guarantee absence of risk.
Subsequent Actions
The operator introduced electronic flight plans with improved weather display and a function to insert geographic coordinates showing SIGMET zones on charts.