Which of the following is NOT a part of the aileron control system?

The correct answer is based on understanding the components of the aileron control system. The aileron control system is designed to manage the aircraft's roll and is primarily composed of elements that directly influence the ailerons' movement on the wings.

The left and right ailerons are the primary control surfaces responsible for rolling the aircraft. Bellcranks serve as mechanical linkages that transmit the driver input from the control columns or sticks to the ailerons themselves, translating movements into effective control surface deflections. Control sticks provide the pilot's input for directing the ailerons, completing the system of control for roll movements.

TAD, which stands for Trim Aid Device, is associated with pitch control and does not have any direct connection to the aileron system. It adjusts the elevator trim to maintain level flight without requiring constant control inputs from the pilot. Since TAD is focused on a different aspect of control—pitch rather than roll—it does not belong to the aileron control system. Thus, identifying TAD as not part of the aileron control system is accurate.