Airworthiness Directives; Aerospatiale Model ATR42 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Aerospatiale Model ATR42 series airplanes, that requires modification of the electrical power supply for the standby horizon indicator. This amendment is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified by this AD are intended to prevent loss of the standby horizon indicator in the event of failure of emergency direct current (DC) power, which could result in reduced controllability of the airplane during instrument flight rules conditions.