FAA Monday will publish a straight-to-final-rule airworthiness directive (AD) ordering Boeing 737 NG operators to double-check elevator aft attach lugs for loose bearings--the same components that were the subject of an emergency AD
The new directive (AD 2010-09-05, available here in .pdf
), which supersedes the March AD, is a result of an in-flight incident in which the aft attach lugs on the left elevator tab control mechanism failed, FAA said. The problem: the jet in the incident had been through the March emergency AD inspections aimed at preventing such failures.
Boeing issued an alert service bulletin on April 16 recommending the new inspections, and FAA based the pending AD on the bulletin, with one notable difference: While Boeing says either new or repaired elevator control mechanisms can be used to replace in-service components and eliminate the need for repetitive checks, FAA will not allow repaired mechanisms to be used. The agency's reasoning, per the AD:
We have not received sufficient data to demonstrate that repaired elevator control tab mechanisms were repaired using procedures that will adequately address the identified unsafe condition. We find that only allowing new Boeing elevator control tab mechanisms as terminating action, as specified by this AD, will adequately address the unsafe condition. We have coordinated this issue with Boeing.
The inspection deadlines vary per specific model based on several factors, but all checks must be done by May 30.