Airworthiness Directives; The Boeing Company Model 747-400, -400D, and -400F Series Airplanes

The FAA is revising an existing airworthiness directive (AD), which applies to certain Model 747-400, -400D, and -400F series airplanes. That AD currently requires revising the FAA-approved maintenance program by incorporating new airworthiness limitations (AWLs) for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. That AD also requires phasing in certain repetitive AWL inspections, and repair if necessary. This AD clarifies the intended effect of the AD on spare and on-airplane fuel tank system components. This AD results from a design review of the fuel tank systems. We are issuing this AD to prevent the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.