Summary
We are revising an earlier proposed airworthiness directive (AD) for all Airbus Model A330-200, A330-200 Freighter, A330-300, A340- 200, and A340-300 series airplanes. The NPRM proposed to require inspecting certain trimmable horizontal stabilizer actuators (THSAs) to determine the number of total flight cycles the THSA has accumulated, and replacing the THSA if necessary. The NPRM was prompted by the results of endurance qualification tests on the THSA, which revealed a partial loss of the no-back brake (NBB) efficiency in specific load conditions. This action revises the NPRM by adding airplanes to the proposed applicability, reducing the proposed compliance times for replacing affected THSAs, and revising the definition of a serviceable THSA. We are proposing this supplemental NPRM (SNPRM) to detect and correct premature wear of the carbon friction disks on the NBB of the THSA, which could lead to reduced braking efficiency in certain load conditions, and, in conjunction with the inability of the power gear train to keep the ball screw in its last commanded position, could result in uncommanded movements of the trimmable horizontal stabilizer and loss of control of the airplane. Since these actions impose an additional burden over those proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.