Airworthiness Directives; Airbus Model A319, A320, and A321 Series Airplanes Equipped With Certain Litton Air Data Inertial Reference Units

This amendment adopts a new airworthiness directive (AD), applicable to certain Airbus Model A319, A320, and A321 series airplanes equipped with certain Litton air data inertial reference units (ADIRU). This AD requires modifying the shelf (floor panel) above ADIRU 3, and, for certain airplanes, modifying the polycarbonate guard that covers the ADIRUs, and the ladder located in the avionics compartment, as applicable. This action is necessary to prevent failure of ADIRU 3 during flight, which could result in loss of one source of critical attitude and airspeed data and reduce the ability of the flightcrew to control the airplane. This action is intended to address the identified unsafe condition.