Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Model 747 airplanes. The existing AD currently requires repetitive inspections to detect damage of the sleeving and wire bundles of the boost pumps of the numbers 1 and 4 main fuel tanks, and of the auxiliary tank jettison pumps (if installed); replacement of any damaged sleeving with new sleeving; and repair or replacement of any damaged wires with new wires. For airplanes on which any burned wires are found, the existing AD also requires an inspection to detect damage of the conduit, and replacement of any damaged conduit with a serviceable conduit. This proposed AD would reduce the initial compliance time and repetitive inspection interval in the existing AD. This proposed AD results from fleet information indicating that the repetitive inspection interval in the existing AD is too long because excessive chafing of the sleeving continues to occur much earlier than expected between scheduled inspections. We are proposing this AD to detect and correct abrasion of the Teflon sleeving and wires in the bundles of the fuel boost pumps for the numbers 1 and 4 main fuel tanks and of the auxiliary tank jettison pumps (if installed), which could result in electrical arcing between the wires and aluminum conduit and consequent fire or explosion of the fuel tank.