Wed, Mar 14, 2007
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)
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