More problems for Airbus systems
A serious in-flight electrical system failure in an Easyjet Airbus A319-111 has prompted a concerning final report from the United Kingdom Air Accidents Investigation Branch. Following four recommendations from the preliminary report in December 2006, the AAIB has now issued a further ten separate recommendations to Airbus and the European Aviation Safety Agency (EASA) on identified safety issues.
The failure in September 2006 deprived the crew of some of its normal flight instruments, autopilot, autothrottle and air traffic control communications, also disabling traffic collision avoidance systems (TCAS) and ATC transponder emissions, according to the report:
The serious incident occurred to an Airbus A319-111 aircraft operating a scheduled passenger flight between Alicante, Spain and Bristol, UK. The aircraft had experienced a fault affecting the No 1 (left) electrical generator on the previous flight and was dispatched on the incident flight with this generator selected off and the Auxiliary Power Unit generator supplying power to the left electrical network.
On the day before the incident a faulty engine driven generator was replaced. The replacement generator tripped off line during a ground run but was satisfactorily reset and declared serviceable. However on the subsequent flight from London Stansted to Alicanti, Spain, the generator tripped again. Checklist procedures having failed to resolve the problem, the auxiliary power unit (APU) was started, and its generator supplied the left electrical network.
The crew consulted the company’s maintenance controllers and were told the flight should continue under minimum equipment list (MEL) provisions and restrictions. When the two flight crews changed over aircraft at Alicante the captains discussed the fault, and an “acceptable deferred defect” (ADD) document was raised, allowing the aircraft to continue in service with the defect, in accordance with the MEL, says the report:
While in the cruise at Flight Level (FL) 320 in day Visual Meteorological Conditions (VMC), with the autopilot and autothrust systems engaged, a failure of the electrical system occurred which caused numerous aircraft systems to become degraded or inoperative. Some of the more significant effects were that the aircraft could only be flown manually, all the aircraft’s radios became inoperative and the Captain’s electronic flight instrument displays blanked.
As the flight proceeded in busy European airspace, the crew was thus denied air traffic control communications, means of position and situation reporting, the ability to transmit data to ATC for traffic separation, and the operation of the cockpit voice recorder. At that point the APU was also not functioning and the flight was reliant on one engine-driven generator.
Faced with those restrictions the crew was left with two alternatives: to divert un-notified from controlled airspace with the risk of engagement by military aircraft because of inability to communicate with an interceptor or to continue as flight planned without ATC communication. Although they had no way of knowing the No 2 transponder was working, they selected the 7700 emergency code. However the co-pilot’s flight instruments were working and the flight was successfully continued to Bristol, following the standard flight profile for the descent, approach and landing, with normal instrument landing systems (ILS) indications displayed on the co-pilot’s primary flight display.
Normal undercarriage selection was unsuccessful but the emergency extension system was used and the landing was normal; however because of the electrical system status the captain had to use the engine fire switches to shut down the engines.
The 14 UKAIB recommendations affecting all Airbus A320 family aircraft – A318, 319, 320 and 321, now include comprehensive and detailed EASA requirements for changes to systems logic, electrics/avionics automation and prioritisation, radiotelephony systems protection, crew/systems interaction, minimum equipment list requirements, and systems inspection/overhaul practices.
