Which Components Are Involved in Landing Gear Retraction and Extension

Posted on October 8, 2025 Harry Walker Aerospace Parts

To reduce aerodynamic drag, aircraft landing gear is often designed to fold into the fuselage or wings. These systems are highly mechanical, integrating a complex network of actuators, braces, locks, sensors, and more that allow the gear to extend and retract safely and reliably. To understand how all these parts work together, we will explore all of these components in this blog, covering their purposes and how they interact to illustrate how landing gear is able to seamlessly operate.

Core Structural Components

Retractable landing gear systems employ diverse elements that provide strength and stability while on the ground while also accommodating the folding or pivoting of gear in specific ways to fit within stowage bays. Some of the most important structural components include:

Main Fittings: These fittings remain fixed at the junction where the landing gear attaches to the airframe, channeling forces from the gear into the structure and providing the anchor around which other gear components pivot during retraction.
Axles: The axle is a cylindrical shaft that directly supports the wheels and transmits loads into the shock strut. During ground operations, the axle rotates freely with the wheels as they turn, and the entire wheel-and-axle assembly pivots or swings as a single unit into the landing gear bay.
Shock Struts: The shock strut is a telescoping piston-and-cylinder assembly charged with hydraulic fluid and compressed nitrogen to cushion the aircraft structure upon touchdown.
Torque Links: Torque links are hinged arms bridging the upper and lower sections of the shock strut to prevent the inner piston of the shock strut from rotating under load. At the same time, they allow the strut to telescope freely during landing impact absorption and when the landing gear retracts or extends.
Bogie Beams and Trailing Arms: A bogie beam is a horizontal beam that supports two or more axles, usually on heavy transports, while a trailing arm is a curved lever arm seen more often on regional or business jets. Both connect beneath the shock strut and pivot at their main retraction points so the wheels tuck neatly into the gear bay.
Drag and Side Braces: Drag braces are rigid bars positioned diagonally between the landing gear strut and the airframe structure to maintain proper geometry. When extended, they lock to resist fore-and-aft loads generated during braking or acceleration, then disengage and fold at their hinge point during retraction. Side braces operate very similarly but are positioned laterally to resist sideways forces.
Trunnions: The trunnion is a reinforced pivot shaft mounted at the upper end of the landing gear assembly, bearing the full weight of the gear and serving as the main hinge around which the entire gear leg swings during retraction and extension.
Landing Gear Doors: Landing gear doors enclose the retracted gear to completely reduce drag. However, some light aircraft omit doors entirely for simplicity.

Actuation and Locking Components

The movement and secure positioning of landing gear is achieved through a variety of actuation methods and locking or backup systems.

Actuators and Valves

Hydraulic Actuators: These actuators rely on pressurized hydraulic fluid to drive the gear between extended and retracted positions. With great force output, they are the most common method used in larger aircraft.
Electro-Hydraulic Actuators (EHAs): In modern aircraft, EHAs combine hydraulic actuation with integrated electrical control so gear can be moved without reliance on centralized hydraulic lines.
Electric Motor–Driven Screw Jacks: On certain light and small aircraft, gear movement is achieved by pairing a threaded screw jack with an electric motor.

For hydraulic-based actuators, valves are also needed to regulate gear movement at the proper times. This primarily relies on types like:

Selector Valves: Selector valves direct hydraulic pressure to the appropriate side of the actuators, extending or retracting the gear as commanded by cockpit controls.
Sequencing Valve: The sequencing valve enforces the correct order of operations, ensuring that gear doors open before gear movement begins, uplocks disengage at the proper time, and doors close after the gear is secured.

Locking and Backup Systems

Once the landing gear has moved into position, the following components keep it functioning as intended:

Uplock Mechanisms: The uplock consists of a hook or latch that engages with a roller or fitting on the gear assembly when retracted to prevent unwanted deployment. The mechanism is then either hydraulically or mechanically released when retraction is commanded.
Downlock Mechanisms: The downlock employs either a mechanical over-center brace or latch that snaps into position when the gear is fully extended so it resists folding unless a positive unlocking action occurs. On some aircraft, hydraulic pressure or spring-assisted locks provide additional security against heavy landing loads.
Emergency Extension Systems: In the event that the primary system fails, smaller aircraft tend to use a gravity-free-fall system, in which uplocks are released and the gear drops into place by its own weight. Larger commercial and military aircraft may use compressed bottles of nitrogen to force hydraulic fluid into the extension side of the actuators. Other emergency extension designs employ a manual crank or handle so the crew can mechanically drive the gear into position.

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In summary, landing gear is able to retract and extend because of a well-thought out system of structural components, actuation systems, locks, and other supplemental parts. When it comes time for landing gear to be serviced, having a dependable source for replacement components is essential to avoid compromising movement or safety. For these needs, turn to Complete Sourcing Solutions.

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