Airworthiness Directives; Boeing Model 747 Series Airplanes

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) T98-25-52 that was sent previously to all known U. S. owners and operators of all Boeing Model 747 series airplanes by individual telegrams. This AD requires revising the Airplane Flight Manual to include procedures to prevent dry operation of the center wing fuel tank override/jettison pumps and, for certain airplanes, to prohibit operation of the horizontal stabilizer tank transfer pumps in flight. This action is prompted by a report indicating that several override/jettison fuel pumps from the center wing tanks and main tanks had been removed because circuit breakers for the override/jettison fuel pumps were tripped, or low pump output pressure was indicated. The actions specified by this AD are intended to prevent contact between the rotating paddle wheel and the stationary end plates within the center wing tank override/jettison fuel pumps or horizontal stabilizer tank transfer pumps due to excessive wear of the pump shaft carbon thrust bearing, which could cause sparks and/or a hot surface condition and consequent ignition of fuel vapor in the center wing tank or horizontal stabilizer tank during dry pump operation (no fuel flowing).