What happened
On 10 June 2006, an Airbus A320, registration EC-JHJ, was preparing for a scheduled public transport flight from Dublin Airport. During pre-departure checks, the flight crew identified that the No 5 left-hand wing spoiler had deployed to the fully open position. The crew managed to reset the system, successfully returning the spoiler to its closed position before takeoff.
Shortly after departing, while climbing through 1,500 ft, a system warning alerted the crew that the same No 5 left-hand spoiler had once again deployed fully. The crew observed that the autopilot was unable to maintain the assigned heading. Transitioning to manual flight, the crew found the aircraft's handling characteristics had changed from normal operations, though they maintained control without difficulty. The crew notified Dublin Air Traffic Control of a flight control issue and elected to return to the airport. The aircraft landed at Dublin without further incident and with no injuries or damage reported.
The investigation
Investigators examined the aircraft's systems and found that the No 5 spoiler would automatically move to the fully open position as soon as hydraulic pressure was applied to the actuator. This deployment occurred even when all electrical connections to the actuator had been severed.
To identify the root cause, the spoiler actuator was removed and sent to the manufacturer for supervised testing. Subsequent analysis at a specialized facility in the UK focused on the electro-hydraulic servo valve within the unit. The investigation established that a seal failure within the spool valve had released debris, which subsequently blocked a port in the servo valve, triggering the unintended movement.