Order Will Affect Some 600 Aircraft

The FAA has issued an Emergency AD (2010-06-51) for all Boeing 737-600, -700, -700C, -800, -900, and -900ER series airplanes. The FAA received a report of failure of the aft attach lugs on the left elevator tab control mechanism, which resulted in severe elevator vibration. The flightcrew diverted from the intended route and made an uneventful landing. Subsequent investigation revealed extensive damage to the elevator tab control system. Severe vibration in this attach point is suspected of allowing rapid wear of the joint, and resulted in failure of the attach lugs. The FAA says that his condition, if not corrected, could result in a loss of aircraft control and structural integrity.

In its investigation, the FAA reviewed Boeing Alert Service Bulletin 737-27A1296, dated March 12, 2010. The service bulletin describes procedures for a detailed inspection to detect discrepancies of the inboard and outboard aft attach lugs of the elevator tab control mechanism. Discrepancies include movement or rotation of the spacer, and gaps between the swage ring and the aft attach lug or between the spacer and the aft attach lug. The service bulletin describes procedures for replacing any discrepant elevator tab control mechanism, including performing the detailed inspection on the replacement part before and after installation. For certain airplanes, the compliance time for the inspection is 12 or 30 days, depending on airplane line number, total accumulated flight cycles, and approval for operation under extended twin operations (ETOPS).

As a result, the FAA is issuing the AD to detect and correct a loose bearing in the aft lug of the elevator tab control mechanism, which could result in unwanted elevator and tab vibration. The consequent structural failure of the elevator or horizontal stabilizer could result in loss of aircraft control and structural integrity. The AD requires accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between this AD and the Service Bulletin,” and also requires reporting the inspection results to Boeing.

FMI: www.faa.gov, www.boeing.com