Airworthiness Directives; Boeing Model 777 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to all Boeing Model 777 series airplanes. The existing AD requires repetitive detailed visual inspections to detect cracking of the coveskin on the outboard leading edge slats; a slat adjustment check; and corrective actions, if necessary. This amendment reduces the repetitive inspection interval, but also provides for an optional modification that would significantly increase the repetitive inspection interval. This amendment also revises the applicability of the existing AD to remove certain airplanes. This amendment is prompted by findings of increased vibration of the coveskins due to air leaking and resonating within the cavity between the fixed leading edge and the coveskin; the vibration can result in fatigue cracking and high fatigue loads. The actions specified in this AD are intended to detect and correct cracking and/or missing pieces of the coveskin 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.