Which of the following is considered a primary flight control?

The primary flight controls are essential for the basic maneuverability of an aircraft, allowing it to perform critical functions during flight. In this context, outboard ailerons are a type of primary control surface located on the wings that manage the roll of the aircraft. They work by creating differential lift across the wings when one aileron moves up and the other moves down, which enables the pilot to control the bank angle and execute turns.

The other options, while important for the control and stability of the aircraft, do not fall under the category of primary flight controls. Flaps, for instance, enhance lift during takeoff and landing but are not used for basic maneuvering in flight. Rudder tabs and trim tabs serve to aid in the adjustment and fine-tuning of control surfaces, but they are secondary to the main control surfaces needed for essential flight operations. Thus, outboard ailerons are recognized as primary flight controls vital for the aircraft's roll control and overall flight command.