Summary
This document revises an earlier proposed airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-10, DC-9-20, DC-9-30, DC-9-40, and DC-9-50 series airplanes, and C-9 (military) airplanes, that would have superseded an existing AD that currently requires repetitive ultrasonic or magnetic particle inspections to detect cracking of the engine pylon aft upper spar straps (caps); and if necessary, replacement of the strap with a new strap, or modification of the engine pylon rear spar straps, which constitutes terminating action for the repetitive inspections. The proposed AD also would have required new, improved repetitive ultrasonic inspections, and corrective actions if necessary. The proposed AD also would have required, among other items, a terminating action for the repetitive inspection requirements. This new action revises the proposed rule by adding airplanes to the applicability. The actions specified by this new proposed AD are intended to detect and correct such fatigue cracking, which could result in major damage to the adjacent structure of the pylon aft upper spar cap, and consequent reduced structural integrity of the airplane. This action is intended to address the identified unsafe condition.