What happened
On 24 August 2010, an Airbus A321-231, registration G-MEDJ, was operating a scheduled night passenger flight from Khartoum, Sudan, to Beirut, Lebanon. While cruising at Flight Level 360 over northern Sudan, the aircraft encountered a series of significant electrical malfunctions.
The flight crew first observed the intermittent failure of the captain's electronic displays, including the Primary Flight Display and Navigation Display, alongside the uncommanded application of left rudder trim. This caused the aircraft to adopt a left-wing-low attitude and deviate from its planned track. During this period, the crew heard a continuous chattering sound from the circuit breaker panels, which was suspected to be relay operation.
As the incident progressed, the co-pilot's displays also began to flicker and go blank. The crew noted that the cockpit lights were intermittently turning off and that the flight control system had reconfigured to Alternate Law. The aircraft exhibited unusual behavior, including shuddering and jolting, and the autothrust system entered a thrust lock mode.
To address the symptoms, the crew followed an ECAM message regarding a fault in the No 1 generator by selecting it to the OFF position. This action temporarily restored normal operations and stopped the chattering noise. However, when the generator was re-engaged, the electrical symptoms returned, prompting the crew to deselect the generator again. The crew subsequently started the APU to power the affected systems. After resetting the rudder trim to neutral, the aircraft returned to a wings-level attitude, and the flight continued manually to Beirut, where it landed safely.
The investigation
An investigation was launched to determine the source of the electrical failure and why both pilots' displays were affected. While the flight recorders (CVR and FDR) had been overwritten due to the delay in reporting, data was recovered from the operator's Flight Data Monitoring programme.
Initial reviews of the flight data confirmed the unusual yaw behavior reported by the crew. The aircraft manufacturer indicated that a reset of the Flight Augmentation Computer (FAC) caused by electrical power interruptions could lead to incremental rudder trim offsets. Multiple interruptions can cumulatively result in significant trim changes.
Findings
- The incident was driven by an electrical power generation system fault.
- The flight crew faced significant challenges because the ECAM did not clearly identify the root cause of the malfunction.
- The aircraft experienced uncommanded rudder trim and intermittent loss of primary flight displays.
- The aircraft's flight control system entered Alternate Law due to the electrical instability.
Safety action
- Safety Recommendation 2010-092: It is recommended that Airbus alert all A320-series operators to the possibility that an electrical power generation system fault may not be clearly annunciated on the ECAM and could lead to uncommanded rudder trim operation.