Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Aerospatiale Model ATR42-500 and ATR72-212A series airplanes. This proposal would require repetitive inspections for cracking of the upper closing rib of the vertical fin, related investigative actions, and corrective actions if necessary. This action is necessary to prevent interference between the upper closing rib and the rudder, which could result in a rudder jam and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.