Airworthiness Directives; Boeing Model 757 Airplanes
We are adopting a new airworthiness directive (AD) for all Boeing Model 757 airplanes. This AD requires installation of an automatic shutoff system for the center tank fuel boost pumps, and installation of a placard in the airplane flight deck if necessary. This AD also requires revisions to the Limitations and Normal Procedures sections of the airplane flight manual to advise the flightcrew of certain operating restrictions for airplanes equipped with an automated center tank fuel pump shutoff control. This AD also requires a revision to the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWLs No. 28-AWL-20 and No. 28-AWL-26. This AD also requires replacement of the fuel control panel assembly with a modified part, installation of two secondary pump control relays for the center tank fuel pumps, other specified actions, and concurrent modification of the fuel control panel assembly. This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent center tank fuel pump operation with continuous low pressure, which could lead to friction sparks or overheating in the fuel pump inlet that could create a potential ignition source inside the center fuel tank; these conditions, in combination with flammable fuel vapors, could result in a center fuel tank explosion and consequent loss of the airplane.