Summary
We propose to supersede an existing airworthiness directive (AD) that applies to certain The Boeing Company Model 707 airplanes, and Model 720 and 720B series airplanes. The existing AD currently requires replacing wiring for the fuel boost pumps and override pumps with new wiring, installing Teflon sleeving on the wiring, and doing associated actions; and doing repetitive inspections to detect damage of the wiring or evidence of a fuel leak. Since we issued that AD, we have determined through service experience that the inspection interval was too long. This proposed AD would reduce the repetitive inspection interval. We are proposing this AD to detect and correct damaged wiring for the fuel boost pumps and override pumps, which could cause electrical arcing that could puncture the conduit containing the wire, and result in a fuel tank explosion or a fire adjacent to the fuel tank.