Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 757 series airplanes, that currently requires repetitive inspections for excessive wear of the internal and external splines of the torque tube couplings of the trailing edge flaps, and replacement of the couplings, if necessary. That AD also provides an optional modification that, if installed, constitutes terminating action for the inspection requirements. This action would expand the applicability of the existing AD and require new inspections of the torque tube assemblies and certain gearbox assemblies and universal joints in the drive system for the inboard trailing edge flaps, and follow-on actions, if necessary. For certain airplanes, this action also would require the previously optional modification and/or a new modification, which would terminate certain inspections. The actions specified by the proposed AD are intended to prevent separations in thedrive system for the inboard trailing edge flaps, which could cause a flap skew condition that could result in damage to the flaps or fuselage, and consequent reduced controllability of the airplane.