Summary
We are revising an earlier proposed airworthiness directive (AD) for the products listed above. That NPRM proposed to require installing new panel assemblies in the main equipment center or on the forward cargo compartment sidewall and removing certain relays from some panels in the main equipment center. That NPRM also proposed to require revising the maintenance program to incorporate Airworthiness Limitations (AWLs) No. 28-AWL-27 and No. 28-AWL-28. That NPRM was prompted by fuel system reviews conducted by the manufacturer. For certain airplanes, this action revises that NPRM by proposing to require prior or concurrent installation of a second fuel crossfeed valve. This action also revises that NPRM by proposing an alternative location for the installation of the new panel assemblies for airplanes that have the optional water system drain plumbing and changing the interconnecting wiring between the P141 panel and the P36 and P37 panels. For airplanes with a deactivated center fuel tank, this action revises that NPRM by proposing an alternative functional test for the left and right override/jettison pumps. We are proposing this supplemental NPRM to prevent possible sources of ignition in a fuel tank caused by electrical fault or uncommanded dry operation of the main tank boost pumps and center auxiliary tank override and jettison pumps. An ignition source in the fuel tank could result in a fire or an 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.