What happened
On January 28, 2007, an Airbus A310, registration CS-TKM, operated by SATA Internacional, was performing a scheduled flight from Ponta Delgada to Lisbon. While established in cruise at 38,000 feet, the aircraft experienced the uncommanded extension of spoiler 6R. The spoiler became stuck in its maximum deflection position.
As the crew executed the required "Spoiler Fault" abnormal checklist, they deactivated the hydraulic pressure to the system. However, the spoiler remained extended. This action caused the autopilot to disconnect, leaving the crew to manage the aircraft manually. The resulting aerodynamic asymmetry induced a Dutch-roll oscillation. To compensate for the drag and the rightward yawing tendency, the crew applied differential engine power by reducing power on engine #2 and increasing power on engine #1. This maneuver inadvertently increased the yawing moment, making the aircraft difficult to control at high speeds. The crew subsequently descended to a lower altitude and reduced speed to regain control, eventually diverting to Santa Maria Airport, where the aircraft landed safely without injuries to the 9 crew members and 181 passengers.
The investigation
The GPIAAF investigation focused on the functionality of the spoiler 6R servo-valve and the crew's response to the malfunction. Maintenance teams inspected the aircraft at Santa Maria and replaced the faulty servo-valve. Subsequent testing of the removed valve on the left wing demonstrated that it also caused uncommanded deployment when pressurized, indicating a hardware failure. While preliminary tests suggested an electrical fault (grounded wiring) within the valve, the specific cause could not be definitively confirmed because the component was lost during transit to the manufacturer in the United States.
Data from the Quick Access Recorder (QAR) revealed that the aircraft had experienced sporadic, unannounced failure warnings during the takeoff roll, which were suppressed by the aircraft's warning priority system (ECAM) during the high-power phase of flight.
Findings
- The primary cause of the incident was the uncommanded deployment of spoiler 6R due to a malfunction in the servo-valve (P/N 73020, S/N 2656-A), likely related to an electrical ground fault.
- The crew's decision to use differential engine power (reducing right engine power and increasing left engine power) acted in the same direction as the yawing moment created by the extended spoiler, thereby exacerbating the aircraft's instability.
- The development of the Dutch-roll was contributed to by the crew's manual flight maneuvers and the fact that the rudder travel limits were reached during high-speed flight.
- The aircraft's warning system inhibited the notification of a previous, momentary spoiler failure during the takeoff phase.