Wednesday, March 14, 2007

FAA: Emergency Airworthiness Directive issued for B737-800

FAAThe U.S. Federal Aviation Administration (FAA) has issued an emergency airworthiness directive (AD) for Boeing Model 737-800 series aircraft. The AD identifies "an unsafe condition that is likely to exist or develop" on airplanes of this type design.

The agency says that it has received a report of seven flight spoiler actuator jams on in-service Model 737-800 Short Field Performance (SFP) airplanes. These were discovered during a routine maintenance walk-around and were believed to have occurred on the previous landing during auto speedbrake extension. Five other instances occurred during spoiler system testing at Boeing prior to delivery. The cause of the failure has been identified as interference within the actuator main control valve.

Here are some details:
The 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 these 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 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. [FAA AD 2007-06-51]
The AD notes that the Boeing 737 Flight Crew Operations Manual Bulletin No. TBC-67, dated March 5, 2007, describes procedures for inspecting spoilers to determine spoiler position after landing and after any rejected takeoff maneuvers. For airplanes on which any spoiler is found in the up position with the speedbrake handle in the down position, the bulletin specifies to contact maintenance. The AD adds additional requirements to those in the aircraft maintenance manual (AMM) for this type.

Click here to read the entire FAA Emergency Airworthiness Directive, AD 2007-06-51.

Click here for a printable ('pdf') version of AD 2007-06-51.