What happened
On July 6, 2001, an Air Transat Canada Lockheed 1011 Tristar, registration C-FTNA, departed Lyon Saint Exupéry for Berlin with 197 passengers and 14 crew members. During the climb, while passing flight level 190, the aircraft encountered severe weather conditions.
While maneuvering to avoid an active storm cell identified on the onboard weather radar, the aircraft was struck by two successive bursts of heavy hail. The first burst lasted approximately two seconds, followed by a brief lull, and then a second, more intense period of hail lasting between 10 and 15 seconds. In response to the impact, the commander executed a steep 60-degree bank to exit the cell, during which the aircraft lost 500 feet of altitude.
Upon assessing the visible damage to the airframe, the crew decided to abort the flight and return to Lyon. The aircraft landed safely at Lyon Saint Exupéry at 17:16. There were no injuries among the passengers or crew.
The investigation
The investigation focused on the aircraft's encounter with the storm and the effectiveness of the onboard weather radar. Investigators examined the cockpit radar displays, which showed varying scales (from 80 NM to 20 NM) and color coding. The investigation also reviewed the meteorological conditions in the region, noting a low-pressure system over France and a convergence line capable of producing violent thunderstorms and hail.
Technical analysis of the aircraft revealed significant structural damage. The hail impacts were widespread across the fuselage, wings, and leading edges. Specific damage included the destruction of position lights, the loss of various components such as antennas and inspection covers, and heavy denting of the engine air intakes. Notably, the cockpit windshields were fractured on their outer layers.
Findings
- The aircraft passed through a highly active cloud cell where the onboard weather radar's color coding did not accurately represent the actual severity of the weather.
- While the radar could detect water droplets (indicating rain), it could not detect dry ice, meaning the presence of hail was not visually apparent on the radar displays.
- The flight path, as cleared by Air Traffic Control, was inherently conflicted with the moving storm cells, which were traveling from east to west.
- The crew's attempt to avoid the most intense part of the storm led them into a zone that appeared less active on the radar but contained intense hailstorms.