What happened
On 25 July 2021, a Boeing 737-800, registered SE-RPE, operated by Norwegian Air Sweden, was en route from Copenhagen-Kastrup to Nice Côte d’Azur. While navigating the Italian-Swiss Alps, the crew was actively performing avoidance maneuvers to bypass several thunderstorm cells.
After successfully circumnavigating one storm cell, the crew requested to return to their original route toward the BORDI waypoint. However, as the aircraft turned, the crew suddenly encountered developing storm clouds embedded within the cloud mass that had been positioned immediately behind the cell they had just bypassed. The crew activated the "Fasten seat belt" sign and prepared for expected turbulence.
Shortly after, the aircraft entered a zone of intense meteorological activity. The flight experienced rapid fluctuations in airspeed and significant vertical and lateral accelerations, including a maximum roll angle of 35.5°. The turbulence was accompanied by heavy precipitation and hail striking the windshield. During this period, a cabin crew member in the aft galley was thrown to the floor, resulting in a broken leg and a dislocated ankle. A second cabin crew member also sustained an ankle injury. The aircraft subsequently exited the cloud cell and landed safely in Nice, where medical personnel were waiting.
The investigation
The BEA examined flight data from the CVR and FDR, radar data from Météo-France, and statements from the flight and cabin crew. The investigation focused on the meteorological conditions in the region, specifically the presence of convective clouds and the effectiveness of the onboard weather radar. Investigators also reviewed the communication between the crew and Milan Air Traffic Control (ACC) and examined the visibility of storm zones on air traffic controller screens.
Findings
- The aircraft encountered severe turbulence and windshear caused by strong convective updrafts within a powerful southwesterly airflow.
- The onboard weather radar may have been unable to detect the developing storm cells earlier due to the presence of a preceding large storm cell, which can mask or "hide" subsequent convective activity.
- Air traffic controllers in the Milan ACC were unable to see storm zones or meteorological phenomena on their radar screens, which limited their ability to provide proactive guidance to the crew.
- The cabin crew injuries occurred while the crew members were performing tasks in the aft galley, having not yet been able to secure themselves or equipment before the sudden onset of the turbulence.