What happened
On 25 February 2015, a Ryanair Boeing 737-800, registered EI-DAC, was operating a scheduled commercial flight from Reus, Spain, to Charleroi, Belgium. During the climb through FL 100, the flight crew permitted the cabin crew to begin service duties. Shortly before reaching the planned en-route altitude of FL 380, the pilots queried the Bordeaux air navigation controller regarding reported turbulence; the controller reported no known turbulence in the sector.
Upon reaching FL 380, the aircraft entered a zone of severe clear air turbulence. The sudden impact caused significant variations in pitch, roll, and airspeed, prompting the crew to disengage the autopilot and auto-thrust. The crew experienced an overspeed warning and the activation of the stick shaker while struggling to stabilize the aircraft. Following a descent to FL 360, the crew re-engaged the automated flight systems. Due to the two cabin crew members sustaining serious injuries during the event, the flight diverted to Bordeaux, landing approximately 35 minutes after the turbulence encounter.
The investigation
The BEA examined flight data recorder (FDR) and cockpit voice recorder (CVR) data, alongside meteorological reports. The investigation analyzed the aircraft's flight path relative to a known jet stream and active SIGMET warnings. Investigators reviewed the crew's flight planning process, specifically their decision to request a track modification to avoid high shear rates, which placed them alongside a known area of turbulence risk.
Findings
- The aircraft encountered severe turbulence despite the crew's efforts to modify the flight path to avoid high-risk areas.
- The crew may have underestimated the risk because the new flight path placed them near a SIGMET-identified air mass, but the controller had reported no recent pilot reports (PIREPs) of turbulence.
- The absence of reported turbulence in the sector likely contributed to the crew's decision to allow cabin service to continue.
- The boundaries of air masses identified in SIGMET warnings are inherently imprecise, and the aircraft entered a turbulent zone approximately 15 NM from the primary area of concern.