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

This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-9-10, -20, -30, and - 40 series airplanes and C-9 airplanes. This amendment requires modification of the spoiler control system, and installation of protective interlock box assemblies in the spoiler circuit. This amendment is necessary to prevent smoke/fire in the flight compartment in the event that the automatic spoiler actuator overheats, and/or loss of the spoiler control system, which could significantly reduce the braking effectiveness of the airplane. This action is intended to address the identified unsafe condition.