Which components are involved in a typical gear retraction/extension system?

• A. Only hydraulic actuators.
• B. Hydraulic actuators, gear doors, door actuators, linkages, control valves, limit switches, and interlocks.
• C. Only gear doors and wheels.
• D. Electrical wiring and lights.

Answer: (B)

Retraction and extension of landing gear is a coordinated hydraulic–mechanical system. The hydraulic actuators provide the actual force to move the gear between the down and up positions. Gear doors, with their own door actuators, open to clear the path for gear during extension and then close to enclose the wheels when retracted. Linkages translate the motion from the actuators to both the gear and the doors, ensuring the whole mechanism moves in a synchronized way. Control valves regulate the flow and pressure of hydraulic fluid, directing movement and controlling speed and sequencing. Limit switches sense the end positions of the gear and doors so the system stops accurately and can signal other components to complete the cycle. Interlocks enforce correct sequencing and prevent hazardous combinations, such as retracting with doors not properly closed or the gear not fully locked. Electrical wiring and lights are part of the aircraft’s electrical system, but they don’t perform the mechanical retraction/extension function, so they aren’t sufficient on their own without the mechanical and hydraulic components listed.