Summary
We are revising an earlier proposed airworthiness directive (AD) for all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The NPRM proposed to require installing an automatic shutoff system for the center and auxiliary tank fuel boost pumps, as applicable; installing a placard in the airplane flight deck if necessary; replacing the P5-2 fuel system module assembly; installing the ''uncommanded ON'' (UCO) protection system for the fuel boost pumps; revising the airplane flight manual to advise the flightcrew of certain operating restrictions for airplanes equipped with an automatic shutoff system; and revising the maintenance program by incorporating new airworthiness limitations for fuel tank systems to satisfy Special Federal Aviation Regulation No. 88 requirements. The NPRM was prompted by fuel system reviews conducted by the manufacturer. This action revises the NPRM by proposing to require updated or additional actions that are necessary for certain airplane configurations. We are proposing this supplemental NPRM (SNPRM) to prevent operation of the center and auxiliary tank fuel boost pumps 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 and auxiliary fuel tanks. These conditions, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.