What happened
On 25 June 2005, an Airbus A3HD-200, registration I-BIKE, was conducting a scheduled passenger flight from Milan to London Heathrow. During the initial approach to Runway 09L in Instrument Meteorological Conditions, the aircraft experienced a failure of the Inertial Reference part of the No 1 ADIRU. This occurred while the aircraft was already operating with an unserviceable No 3 ADIRU.
During the approach, the aircraft deviated from the glideslope, triggering EGPWS warnings. The crew, attempting to manage the technical issues, decided to perform a go-around. During this phase, the crew elected to turn the No 1 ADIRU rotary switch to the OFF position. This action, which was not required by the ECAM instructions, caused further degradation of the aircraft's systems, including the loss of autopilot, autothrust, and the transition of flight control laws to DIRECT law.
As the aircraft prepared for a second approach, the loss of air data from the No 1 and 3 ADIRUs rendered the normal landing gear extension system inoperative. The crew successfully deployed the landing gear using the emergency gravity extension system. Upon landing, the loss of air data also caused the nosewheel steering to become unavailable. The aircraft eventually came to a stop on an adjacent taxiway after a right turn using asymmetrical braking.
The investigation
The AAIB examined data from the Flight Data Recorder and Cockpit Voice Recorder, alongside a review of the aircraft's maintenance history. The investigation established that the aircraft had been dispatched with a known defect in the No 3 ADIRU, which was permitted under the operator's Minimum Equipment List.
Investigators also reviewed the crew's communication with Air Traffic Control. It was noted that while the commander transmitted a PAN call, the specific nature of the emergency was not clearly understood by controllers, partly due to the commander's heavy accent and a double transmission that masked the message. This resulted in the airport Rescue and Fire Fighting Service not being placed on Local Standby.
Findings
- The crew's decision to switch off the No 1 ADIRU instead of following the ECAM checklist led to the loss of additional critical aircraft systems.
- The loss of both No 1 and No 3 ADIRU air data caused the landing gear extension system to become inoperative, necessitating a gravity extension.
- The loss of air data also caused the flight control laws to revert to DIRECT law and rendered the nosewheel steering inoperative.
- The commander's failure to use standard MAYDAY protocol contributed to ATC not being fully aware of the severity of the situation.