Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Model 757 airplanes. The existing AD currently requires sealing the fasteners on the front and rear spars inside the left and right main fuel tanks and on the rear spar and lower panel of the center fuel tank. That AD also requires inspections of the wire bundle support installations to verify if certain clamps are installed and if Teflon sleeving covers the wire bundles inside the left and right equipment cooling system bays, on the left and right rear spars, and on the left and right front spars; and corrective actions if necessary. This proposed AD would also require sealing the additional fasteners on the rear spar inside the left and right main fuel tanks. This proposed AD results from a fuel system review conducted by the manufacturer. We have received reports from the manufacturer that additional fasteners in the main fuel tanks must be sealed for lightning strike protection. We are proposing this AD to detect and correct improper wire bundle support installation and sleeving and to prevent improperly sealed fasteners in the main and center fuel tanks from becoming an ignition source, in the event of a fault current or lightning strike, which could result in a fuel tank explosion and consequent loss of the airplane.