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

We are adopting a new airworthiness directive (AD) for certain Boeing Model 747-400, -400D, and -400F series airplanes. This AD 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. This AD also requires the initial inspection of certain repetitive AWL inspections to phase in those inspections, and repair if necessary. 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.