What happened
On 22 October 2005, an Airbus A319-131, registration G-EUOB, was operating a scheduled passenger flight from London Heathrow to Budapest. While climbing through FL200 in dark, clear weather conditions near Clact and Essex, the crew experienced a sudden audible 'clunk' followed by a significant electrical failure.
The incident resulted in the immediate loss of both the commander’s and co-pilot’s primary flight and navigation displays, as well as the ECAM upper display. Additionally, the autopilot and autothrust disconnected, accompanied by Master Warning and Master Caution tones. The flight deck lighting was also severely impacted, with the loss of most integral lights on the overhead, glareshield, and pedestal panels. The crew also lost the intercom system, and the radio became unpowered, preventing a 'MAYDAY' call to Air Traffic Control.
The investigation
The AAIB investigation focused on the sequence of electrical failures and the crew's ability to manage the emergency. The investigators found that the crew maintained aircraft attitude by using the external night horizon and the standby horizon, though the latter was not illuminated due to low ambient light in the cockpit.
To restore the affected systems, the co-pilot performed ECAM procedures. The investigation established that the primary flight instruments and most systems were restored after approximately 90 seconds once the crew selected the AC ESS FEED push button switch to the 'ALTN' position. However, the crew's ability to execute these steps was hindered because the necessary corrective action was buried deep within the list of warning messages and was not initially visible on the remaining display.
Findings
- The simultaneous loss of both primary flight and navigation displays, along with the ECAM upper display, occurred during a critical phase of flight.
- The crew's ability to manage the failure was delayed because the required corrective action was not immediately visible on the ECAM lower display.
- The lack of cockpit lighting made it difficult for the crew to identify and action the necessary ECAM procedures.
- The investigation noted that the aircraft's standby horizon remained powered due to specific wiring (ISIS), though it was not lit.
Safety action
The AAIB issued several safety recommendations to the manufacturer, Airbus:
- A recommendation to review ECAM actions for the A320 series to ensure displays can be recovered more quickly during simultaneous failures.
- A recommendation to identify aircraft with single power supplies to the standby artificial horizon and advise operators of the implications.
- A recommendation to revise the Flight Crew Operating Manuals to accurately reflect the power source configurations for the standby horizon.
- A recommendation to reconsider the permissibility of operating with an inoperative ECAM lower display unit under the Master Minimum Equipment List (MMEL).