Final answer:
The #3 hydraulic system powers the ailerons and spoilers, which are control surfaces on an aircraft.
Step-by-step explanation:
The #3 hydraulic system powers the ailerons and spoilers, which are control surfaces on an aircraft.
Control surfaces determine the direction and movement of an aircraft. The ailerons control the roll or banking motion of the aircraft, while the spoilers help in reducing the lift and increasing the drag during landing and reducing speed.
The other options listed, such as landing gear and retraction, inboard brakes, thrust reversers, and elevators, are powered by different hydraulic systems or other mechanisms.