What happened
On July 14, 2010, an Air France Airbus A300-211 (registration F-GMZB) was performing a passenger flight from Ajaccio to Orly. During the approach, while positioned near the OKRIX holding pattern at flight level 180, the aircraft encountered extreme turbulence caused by severe thunderstorm activity in the Paris region.
The turbulence was so intense that the aircraft experienced a vertical wind gradient of 25 knots in approximately two seconds, causing the airspeed to drop from 202 knots to 178 knots. This sudden change caused the aircraft's angle of attack to increase to approximately 13 degrees, triggering the Alpha Prot (angle of attack protection) system and causing the autopilot to disengage. The co-pilot took manual control, applying maximum thrust (TOGA) and managing significant longitudinal and lateral control inputs to stabilize the aircraft. Despite experiencing vertical load factors ranging from -0.03g to +1.89g and significant rolling motions, the aircraft remained within its certified flight envelope and landed safely at Orly without further incident.
The investigation
The BEA investigation utilized flight data recorder analysis, crew reports, and radar-radio data provided by the DSNA. The investigators examined the meteorological conditions, specifically analyzing ASPOC images from Météo France, which confirmed the presence of several cumulonimbus cells moving toward the OKRIX holding pattern at the time of the event.
The investigation also reviewed air traffic control (ATC) communications. During the period in question, landings at both Orly and Rozen (CDG) were suspended due to thunderstorms. The investigation found that the controller was managing a high volume of requests from various crews attempting to avoid convective activity, leading to high frequency occupancy and complex traffic management challenges.
Findings
- The primary cause of the incident was the encounter with severe turbulence within a thunderstorm.
- The aircraft's angle of attack protection activated and the autopilot disengaged due to the extreme vertical wind gradient.
- The air traffic controller faced significant difficulties in managing traffic because the thunderstorm cells were not directly visible on the controller's radar screen.
- While the controller had access to meteorological data (ASPOC), this information was not integrated into the radar display, preventing effective assistance to crews attempting to avoid convective zones.
Safety action
- The BEA recommended that the DGAC establish a high-priority timeline for integrating the visualization of thunderstorm and turbulence zones directly onto the radar screens used by en-route and approach controllers, along with defined procedures for using this information.