Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 777 series airplanes, that currently requires repetitive inspections to detect cracking of the coveskin on the outboard leading edge slats, and corrective actions, if necessary. The existing AD also provides for an optional modification that significantly increases the repetitive inspection interval. This action would expand the applicability of this AD by mandating the currently required inspections, and corrective actions, if necessary, for additional airplanes. Also, for airplanes on which the optional modification has been accomplished, this action would require a new one-time inspection for undersized seal inserts in the spanwise bulb seals on certain slats, and replacement of seal assemblies with new assemblies, if necessary. These actions are necessary to detect and correct cracking or missing pieces of the coveskin, or undersized seal inserts installedin the spanwise bulb seals, on the outboard leading edge slats on the wings, which could result in skin separation or structural damage to the leading edge slats and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.