Summary
We are revising an earlier proposed airworthiness directive (AD) for certain transport category airplanes identified above. The original NPRM would have required modifying the fuel boost pumps. The original NPRM resulted from a fuel boost pump found with blown thermal fuses and a fractured thrust washer. This action revises the original NPRM by referring to new service information, which would require more work. We are proposing this supplemental NPRM to prevent failure of the fuel boost pumps, which could lead to the potential of ignition sources inside fuel tanks. This condition, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.