Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 767-400ER series airplanes. This proposal would require repetitive high frequency eddy current inspections of the aft lower lugs of the deflection control track of the outboard flap for cracks, and replacement of any cracked deflection control track with a new track assembly. This action is necessary to prevent fatigue cracking in the aft lower lug run-out region of the deflection control track. Fatigue cracking of the deflection control track, if not detected and corrected in a timely manner, could result in the loss of the secondary load path for the outboard flap, resulting in the loss of the outboard flap and consequent reduced controllability of the airplane in the event that the primary load path also fails. This action is intended to address the identified unsafe condition.