What happened
On 18 October 1998, an A320-231, registration EI-TLI, was operating a public transport flight from Rome to Dublin. While the aircraft was 23 NM southeast of Dublin Airport, the crew observed a low-pressure warning for the blue hydraulic system on the ECAM. During the execution of emergency checklists, the aircraft was struck by lightning, which left scorch marks on the radome.
As the aircraft prepared for landing, the crew noted that the number 3 starboard spoiler was stuck in the upward position. The flight crew found it increasingly difficult to maintain directional control, particularly as the aircraft slowed to approach speeds. The captain eventually disconnected the autopilot to manually manage the aircraft. Upon touchdown, a severe roll to the right occurred, necessitating the use of full left aileron to prevent the engine pod or winglet from contacting the runway. Following the landing roll, a hydraulic oil leak was identified at the starboard spoiler actuator.
The investigation
The investigation focused on the mechanical failure of the spoiler system and the timing of the manufacturer's retrofit programs. It was established that the starboard spoiler actuator was leaking hydraulic fluid due to a failure in the servocontrol.
Technical analysis revealed that the failure was caused by a fatigue break in the piston rod bearing, a result of improper machining in the actuator housing. This specific defect had been identified by the manufacturer as early as 1993. The investigation also examined the maintenance and supply chain logistics, noting that the aircraft's servocontrols had not yet been replaced under the recommended Service Bulletins, despite the known risks of the component failure.
Findings
- The primary cause of the handling difficulties was the failure of the starboard spoiler actuator, which left the spoiler stuck in the up position.
- The aircraft's control characteristics were further compromised by a lightning strike during the emergency procedure.
- The retrofit program for the defective servocontrols was insufficient; the manufacturer's supply of exchange units was inadequate, leading to delays in implementation.
- The existing Service Bulletin timelines were too lenient, as they allowed unmodified components to remain in service for extended periods based on flight cycles rather than time.
- The use of an external maintenance organization for 'C' checks contributed to the delay in performing the necessary component replacements.