What happened
On 26 December 2014, an Airbus A3/A330 operated by XL Airways France, registration F-GRSQ, was conducting a commercial passenger flight from Saint-Denis de la Réunion to Marseilles. During the cruise phase over the Mediterranean Sea, the aircraft experienced a progressive degradation of its navigation systems.
At approximately 10:34 UTC, IRS 3 transitioned from NAV mode to ATT mode. While the crew was monitoring a known drift in IRS 2, the automated flight systems eventually rejected the remaining inertial references due to a lack of consistency between the units. At 13:36, the autopilot, autothrust, and flight director disconnected, and the flight management system lost position and flight plan data.
Following this, a series of actions led to the aircraft entering a state where the crew had to manage the flight without primary navigation displays. During the period of instability, a sequence of events resulted in the aircraft's inertial reference systems undergoing a re-alignment process. The crew eventually managed to divert the aircraft to a safe landing.
Investigation Findings
The investigation focused on the sequence of events that led to the loss of situational awareness. The investigation found that the aircraft's inertial reference systems underwent an in-flight alignment, which was likely triggered by manual interventions or system responses to the loss of data.
Crucially, the investigation noted that the aircraft's hardware and software were functioning, but the crew was faced with a complex, rapidly evolving situation. The investigation also identified that the physical layout of the cockpit controls and the way information was presented contributed to the difficulty in managing the emergency. The investigation highlighted that the lack of clear, actionable information during the transition to manual flight made it difficult for the crew to maintain the flight path.
Safety Recommendations
The investigation concluded that the primary cause was the complex interaction between the crew's attempts to troubleshoot the system and the automated responses of the aircraft. The investigation noted that the lack of clear, unambiguous information during the failure made it difficult for the crew to maintain situational awareness.
While no specific safety recommendations were made regarding the aircraft's design, the investigation emphasized the importance of human factors in the design of cockpit interfaces and the clarity of automated system responses during critical flight phases.