Airworthiness Directives; Airbus Airplanes

We are adopting a new airworthiness directive (AD) for all Airbus Model A300 series airplanes; Model A300 B4-600, B4-600R, F4-600R series airplanes, and Model A300 C4-605R Variant F airplanes (collectively called Model A300-600 series airplanes); and Model A310 series airplanes. This AD was prompted by reports of partial loss of no-back brake (NBB) efficiency on the trimmable horizontal stabilizer actuator (THSA). This AD requires an inspection to determine THSA part numbers, serial numbers, and flight cycles on certain THSAs; and repetitive replacement of certain THSAs. We are issuing this AD to prevent loss of THSA NBB efficiency, which, in conjunction with the inability of the power gear to keep the ball screw in its last commanded position, could lead to an uncommanded movement of the horizontal stabilizer, possibly resulting in loss of control of the airplane.