What happened
On 15 August 2003, an EasyJet Boeing 737-33V, registration HB-III, was operating flight EZS 903 departing from Geneva. During the flight, the aircraft encountered a severe thunderstorm cell in the region of Oyonnax, France, approximately 35 km west of Geneva. The aircraft flew directly into a shower of heavy hail, with some hailstones reported to be as large as 40 to 50 mm in diameter. The crew subsequently declared a distress situation due to the intense weather. While the aircraft survived the encounter, the event caused significant operational disruption.
The investigation
The investigation, based on findings from the Air Accident Investigation Bureau, examined the meteorological conditions, technical functionality of the aircraft, and the operational performance of both the flight crew and air traffic control (ATC). Investigators analyzed weather radar images from MeteoSwiss and the aircraft's onboard Honeywell RDR-4B radar, as well as cockpit voice recorder data. The inquiry also reviewed the communication between the flight crew and ATC, and the dissemination of meteorological warnings such as SIGMET messages.
Findings
- The primary cause of the accident was the aircraft flying into a hail shower embedded in a thunderstorm cell because of the inadequate use of onboard weather radar information.
- The flight crew failed to prioritize avoiding thunderstorm cells over other tasks, such as operating the Flight Management System (FMS).
- Although the storm cell should have been visible on the aircraft's electronic horizon situation indicators at least two minutes prior to the encounter, the crew continued on a heading that led into the hail.
- There were notable shortcomings in Crew Resource Management (CRM), as the copilot did not sufficiently alert the commander to the need to prioritize weather avoidance.
- Air traffic controllers did not transmit specific meteorological hazards to the crew, and no SIGMET message regarding the hail was issued for the region that morning.
- No technical faults were found with the aircraft's airworthiness, though the localizer for runway 05 ILS was out of order at the time.
Safety action
Following the investigation, safety recommendations were issued to the Federal Office for Civil Aviation. These include requirements for air traffic personnel to systematically use available weather radar information when dangerous situations arise. Additionally, recommendations were made to ensure that specific weather information received from flight crews is immediately disseminated to relevant air traffic sectors and forwarded to meteorological services to facilitate the timely issuance of SIGMET messages.