Airworthiness Directives; McDonnell Douglas Model DC-9-10, DC-9-20, DC-9-30, DC-9-40, and DC-9-50 Series Airplanes

This amendment supersedes an existing 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 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. This amendment requires new, improved repetitive ultrasonic inspections, and corrective actions if necessary. This amendment also requires, among other items, a terminating action for the repetitive inspection requirements. The actions specified by this AD are intended to detect and correct 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.