What happened
On January 19, 2010, an Air France Airbus A320-211, registration F-GHQH, was climbing to FL150 from Paris-Orly to Toulouse-Blagnac when the crew encountered a series of electrical malfunctions. The flight crew first observed a DMC alarm, followed by an amber "LOW PRESS" alarm on the blue hydraulic circuit. Shortly thereafter, the cockpit screens on the captain's side went dark, and a continuous stream of amber alarms began to populate the flight deck. The frequency of these alarms increased rapidly, making them difficult to process.
To manage the workload, the captain transferred pilot flying duties to the first officer. The crew decided to limit the cruise altitude to FL230. As the alarms continued for approximately fifteen minutes, the crew noted that the alerts were specifically related to equipment powered by the left engine generator (IDG1). To stabilize the situation, the captain declared a state of distress (MAYDAY) to prioritize airspace and reduce radio communications. After identifying the generator 1 alarm, the crew followed the checklist to switch the generator to the OFF position, which stopped the cascade of messages. The crew then started the APU to ensure electrical redundancy and continued the flight to Toulouse.
The investigation
The investigation focused on the electrical system and the sequence of failures. While the crew's primary concern was a potential short circuit or fire, the investigation found that the aircraft's monitoring systems did not register a formal undervoltage because the voltage drops were too brief to trigger the standard thresholds.
Subsequent maintenance performed on the following flight revealed that the electrical harness connector linking the IDG to engine 1 showed signs of carbonization on one of the phases. Further inspection of the connector showed that contact corrosion on phase B had increased local resistance, creating a hot spot that damaged the connector. This damage caused intermittent power interruptions to all systems on AC BUS 1.
Findings
- The primary cause of the multiple intermittent alarms was a faulty connection in the engine generator harness.
- The electrical instability was caused by insufficient tightening of the harness connector, which led to contact corrosion and subsequent carbonization.
- The voltage drops were too short in duration to trigger the aircraft's automatic undervoltage protection thresholds, preventing the crew and the ECAM from identifying the specific source of the failure immediately.
- The crew's decision to declare a MAYDAY helped manage the high workload and noise levels in the cockpit caused by the continuous alarms.
Safety action
- It was noted that while newer Souriau-brand connectors are less susceptible to this issue, older Cannon-brand connectors remain a potential risk.
- Following similar occurrences, Airbus issued an information bulletin and updated the Quick Reference Handbook (QRH) with a "DISPLAY UNIT FAILURE" procedure.
- EASA subsequently issued Airworthiness Directive (AD) 2011-0142.