Elevator tab control mechanism inspection info 737-6/7/8/900

The aircraft manufacturer has recently received a report from an operator where the failure of the aft attach lugs on the left elevator tab control mechanism resulted in unwanted elevator freeplay vibration during flight. Investigation revealed that the fractured aft attach lugs on the elevator tab control mechanism allowed freeplay of the aft end of the uncontrolled motion of the tab control
mechanism, which allowed freeplay of the forward end of the elevator tab control rods.

This message shows photos of the location of the tab control mechanism attach lugs and also shows the parts to inspect. The inspection should be accomplished per the ref Maintenance Task Cards. One addition to the inspection procedure is to add a step to include a „finger feel check“ of the lug bearing spacer.

The first SB 737-27A1296 states to perform detailed inspections of the bearings in the elevator control tab mechanism aft attach lugs. Look for gaps and loose parts. If there are gaps or loose parts, replace the elevator control tab mechanism.
The second SB 737-27A1296 does a more enhanced inspection than the inspection in SB 737-27A1296 and continues with repeat inspections until the elevator tab control mechanism is replaced. The more enhanced inspection includes using a feeler gage at specific locations to check for gaps. The inspections in this SB will detect a loose bearing in the aft attach lugs of the elevator tab control mechanism. The pictures below are for information and extra awareness of this inspection. Also a failed mechanism is shown on one of the pictures.


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