Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Boeing Model 747 series airplanes. The existing AD currently requires repetitive detailed inspections of the aft pressure bulkhead for indications of "oil cans'' and previous oil can repairs, and corrective actions, if necessary. An oil can is an area on a pressure dome web that moves when pushed from the forward side. This proposed AD would reduce the compliance time for the initial detailed inspection and clarify the applicability. This proposed AD results from a report that cracks in oil-canned areas were found during an inspection of the aft pressure bulkhead. We are proposing this AD to detect and correct the propagation of fatigue cracks in the vicinity of oil cans on the web of the aft pressure bulkhead, which could result in rapid decompression of the airplane and overpressurization of the tail section, and consequent loss of control of the airplane.