Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 777-200, -200LR, -300, and -300ER series airplanes. The original NPRM would have required revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness by incorporating new limitations for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. The original NPRM would also have required the initial performance of certain repetitive inspections specified in the AWLs to phase in those inspections, and repair if necessary. The original NPRM resulted from a design review of the fuel tank systems. This action revises the original NPRM by reducing the initial compliance time of certain repetitive inspections, adding more airplanes, and referring to new service information. We are proposing this supplemental NPRM to prevent the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, ormaintenance actions, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.