Airworthiness Directives; The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP Series Airplanes
We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires adding two new indicator lights on a certain panel to inform the captain and first officer of a low pressure condition in the left and right override/jettison pumps of the center wing tanks. This AD also requires replacing the left and right override/jettison switches on the M154 fuel control module on the P4 panel with improved switches and doing the associated wiring changes. This AD also requires, for certain airplanes, installation of a mounting bracket for the new indicator lights. This AD also requires a revision to the maintenance program to incorporate airworthiness limitation No. 28-AWL-22. This AD also requires a revision to the airplane flight manual to advise the flightcrew what to do in the event that the pump low pressure light on the flight engineer's panel does not illuminate when the pump is selected off. This AD was prompted by fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent uncommanded operation of the override/jettison pumps of the center wing tanks, and failure to manually shut off the override/ jettison pumps at the correct time, either of which could lead to an ignition source inside the center wing tank. This condition, in combination with flammable fuel vapors, could result in a center fuel tank explosion and consequent loss of the airplane.