Airworthiness Directives; Aerospatiale Model ATR42 Series Airplanes and Model ATR72 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Aerospatiale Model ATR42-200, -300, -320, and - 500 series airplanes; and Model ATR72 series airplanes; that requires replacement of a certain Automatic Takeoff Power Control System (ATPCS) test selector switch with a different test selector switch. This action is necessary to prevent shorting of a contact in the ATPCS test selector switch due to abnormal wear of contact surfaces, which could result in dual engine power drop with associated loss of both alternating current wild and main hydraulic power during ground maneuvers, and consequent reduced controllability of the airplane and increased flightcrew workload. This action is intended to address the identified unsafe condition.