Investigators are recommending that pilots be trained more rigorously to fly with sole reference to standby instruments following a serious incident in which a British Airways Airbus A319 suffered an extensive loss of electrical power.
The UK Air Accidents Investigation Branch has also advised BA to review its reporting procedures after the inquiry team learned about the incident only six days later, the jet having remained in service in the meantime.
After a two-year investigation, the AAIB has been unable to determine the reason for the power loss, which affected the jet's left-hand electrical network, shortly after it departed London Heathrow for Budapest on 22 October 2005. But it suspects one of the generator control units detected a false electrical current differential-protection condition.
Failure of the network caused the loss of both pilots' primary flight and navigation displays, the upper electronic centralised aircraft monitor (ECAM) display, cockpit lighting, the radio and the intercom. The auto-thrust and autopilot also disconnected.
"This and other similar incidents show that there is at least one unforeseen failure mode on A320 family aircraft which can cause the simultaneous loss of the captain's and co-pilot's electronic flight instruments and the upper ECAM display," says the AAIB.
If the primary displays are unavailable, the A319 can be flown on standby instruments - including a horizon, altimeter, airspeed indicator and compass - but the AAIB says: "The flight crew had not received any formal training on how to operate A320-family aircraft by sole reference to the standby instruments."
Technical log entries contained hardly any details of the event and, as a result, failed to trigger any investigation, and mailed and faxed air safety reports did not arrive for days, if at all. "A substantial period of time passed before the significance of this incident was recognised by the airline," says the AAIB.
Most of the systems were recovered about 90s after the failure. The captain incorrectly believed that the fault lay in a transformer rectifier and, despite the alarming nature of the initial failure, opted to continue to Budapest.
The AAIB questions whether particular procedures listed on the lower ECAM could have been prioritised differently to speed recovery, but Airbus rejects this suggestion. It says the ECAM prioritisation was drawn up after analysing many different safety issues and changing them would require complex follow-up verification and approval. However, it has addressed concerns over power supply to standby instruments.
Source: Flight International
