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.
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.
Attempts by the flight crew to reconfigure the electrical system proved ineffective and the aircraft systems remained in a significantly degraded condition for the remainder of the flight, making operation of the aircraft considerably more difficult. The flight crew were unable to contact air traffic control for the rest of the flight. The aircraft landed uneventfully at Bristol, with the radios and several other systems still inoperative.
The incident was reported to the Air Accidents Investigation Branch (AAIB) by the operator at 1452 hrs local on 15 September 2006. An investigation was commenced shortly thereafter. France, as the state of aircraft manufacture and design, appointed an Accredited Representative from the BEA1. Assistance was also given by the aircraft manufacturer, Airbus.
The reasons why the electrical system could not be reconfigured by the flight crew could not be established.
The investigation identified the following causal factors in this incident:
An intermittent fault in the No 1 Generator Control Unit, which caused the loss of the left electrical network
An aircraft electrical system design which required manual reconfiguration of the electrical feed to the AC Essential busbar in the event of de-energisation of the No 1 AC busbar, leading to the loss or degradation of multiple aircraft systems, until the electrical system is reconfigured
The inability of the flight crew to reconfigure the electrical system, for reasons which could not be established
Master Minimum Equipment List provisions which allowed dispatch with a main generator inoperative without consideration of any previous history of electrical system faults on the aircraft
Inadequate measures for identifying Generator Control Units repeatedly rejected from service due to repetition of the same intermittent fault
Preliminary information on the progress of the investigation was published in AAIB Special Bulletin S9/2006 on 13 December 2006 and four Safety Recommendations were made. Ten additional Safety Recommendations are made in this report.
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