Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747 series airplanes. The existing AD currently requires repetitive inspections to detect cracks at certain stringer fastener locations; and repair, if necessary. For certain airplanes, the existing AD requires a modification in certain areas where reports indicate that cracking was prevalent. This modification terminates the repetitive inspections only for those areas, and is also an option for other airplanes affected by the existing AD. This proposed AD would require one-time inspections at a reduced inspection threshold of areas that may have Alodine-coated rivets installed, and repair if necessary. This proposed AD results from a report of cracking discovered in a skin lap joint that was previously inspected using the eddy current method. We are proposing this AD to prevent rapid decompression of the airplane due to disbonding and subsequent cracking of the skin panels.