Sticky Spoilers On SFP-Equipped Aircraft To Blame

The FAA has issued Emergency airworthiness directive (AD) 2007-06-51 to all owners and operators of Boeing Model 737-800 series airplanes. The agency states it has received a report of seven flight spoiler actuator jams on Model 737-800 Short Field Performance (SFP) airplanes.

"Two reports involved in-service airplanes that were discovered during a routine maintenance walk-around and were believed to have occurred on the previous landing during auto speedbrake extension," the AD states. "Five other reports occurred during spoiler system testing at Boeing prior to delivery. An additional two reports of spoiler actuator input lever binding were identified during bench testing after Boeing began to investigate this issue."

The agency adds two in-service failures of flight spoilers resulted in the spoilers not retracting after the speedbrake handle was moved to the DOWN position after landing, on a Boeing Model 737-800 airplane equipped with an SFP package. In both of those cases, the spoiler was discovered in the full-extended position during a routine maintenance walk-around. The spoiler remained in the full-extended position after cycling of the speedbrake handle.

"Further investigation revealed that the spoiler actuator failure is most likely to occur when the speedbrakes are deployed on the ground (automatically or manually) for either a rejected takeoff or normal landing. The takeoff configuration warning will not sound if any flight spoiler remains extended with the speedbrake handle in the DOWN position."

The FAA states the cause of the failure has been identified as interference within the actuator main control valve. This condition, if not corrected, could result in a spoiler actuator hardover, which could cause the spoiler surface to jam in the fully extended position. Two or more hardover failures of the spoiler surfaces in the up direction on the same wing, if undetected prior to takeoff, can cause significant roll and consequent loss of control of the airplane.

FMI: Read The Complete AD Here (.pdf)