What is aircraft landing gear, and how does it work?
Learn what aircraft landing gear means, its parts and functions, how fixed and retractable systems work, and what common faults indicate.
Aircraft landing gear is the undercarriage that supports an aeroplane on the ground and enables it to taxi, take off and land. The system includes wheels, tyres, shock struts, brakes and steering, plus retraction, locking and indication equipment where fitted. It carries weight, absorbs touchdown loads and preserves control.
What does landing gear mean on an aircraft?
Landing gear means the complete ground-support and ground-control installation, not merely the wheels. In aviation, and throughout our Aviation & Real-World Flying coverage, landing gear and undercarriage are commonly used for the same system.
Most aeroplanes use wheeled gear attached to the fuselage, wings or both. Specialised aircraft may use floats, skis or skids, while amphibious aircraft can combine floats with retractable wheels. Landing gear is a collective term: a three-legged aeroplane has one landing gear system, not three separate landing gears. The standard spelling is two words; landinggear is not standard aviation usage.
Aircraft landing gear parts and functions
The parts of aircraft landing gear divide the work between supporting the airframe, absorbing energy, controlling direction and stopping the aircraft.
| Part | Function |
|---|---|
| Legs, trunnions, axles and braces | Carry vertical, fore-and-aft and sideways loads between the wheels and airframe. Drag and side braces also keep retractable gear correctly aligned. |
| Shock strut or spring | Absorbs touchdown and taxi loads. An oleo-pneumatic strut uses compressed gas as the spring and metered hydraulic fluid to damp the movement; lighter aircraft may use spring steel, composites, rubber bungees or other arrangements. |
| Wheels and tyres | Provide the runway contact patch and carry the load. Tyre size and pressure are type-specific: transport aircraft use high-pressure tyres, while bush aircraft may use large, low-pressure tyres on soft surfaces. |
| Main-wheel brakes | Convert the aircraft's motion into heat. Anti-skid systems detect excessive wheel slip or deceleration and reduce brake pressure before a tyre remains locked. |
| Steering and shimmy damping | Turn the nose wheel or tailwheel and suppress rapid wheel oscillation. Steering may use rudder pedals, a separate tiller, differential braking or a combination. |
| Actuators, doors and locks | Extend and retract movable gear, streamline the openings and hold each leg securely in the selected position. |
| Position and weight-on-wheels sensors | Report whether the gear is down, locked or moving. Weight-on-wheels switches also change other systems between flight and ground logic. |
The tyres and shock absorbers deal mainly with vertical energy, but the structure must also withstand braking loads and crosswind side loads. Flaps, ground spoilers and reverse thrust help an aircraft land and stop, but they are not parts of the landing gear.
How does an aircraft landing gear system work?
A fixed landing gear remains permanently extended, while a retractable system moves the gear between reinforced bays and the landing position. Hydraulic actuation is common on larger aircraft; electric motors are found on many lighter types, and some installations use pneumatic power or a combination of systems.
How retractable landing gear extends and retracts
Retractable gear follows a controlled sequence so that doors, legs and locks do not interfere with one another.
- The pilot selects the gear: a cockpit lever or switch sends an electrical, hydraulic or mechanical command. Many aircraft have a weight-on-wheels interlock intended to prevent accidental retraction on the ground.
- Doors and uplocks release: gear doors open where required, and an uplock releases each leg from its retracted position. Some designs leave certain doors open whenever the gear is down.
- Actuators move the gear: hydraulic rams, electric motors or gravity and airflow move the legs through their travel.
- Downlocks engage: mechanical hooks or over-centre braces secure the extended gear. On most designs, hydraulic pressure alone is not what keeps the gear safely down.
- Sensors confirm the position: cockpit indications change only when the relevant locks and position switches agree. An intermediate or disagreeing state produces an in-transit or unsafe indication.
- The sequence reverses after take-off: once safely airborne, the gear unlocks, retracts and is held by uplocks. Doors then close if the design uses fully enclosed bays.
An alternate extension system may release the uplocks and let gravity and airflow lower the gear, or it may use a hand pump, backup pressure source or electric motor. There is no universal emergency method. For a specific transport-aircraft example, our explanation of how the Airbus A320 hydraulic systems power the landing gear and other services shows how gear operation fits into a larger aircraft system.
What happens to the landing gear at touchdown?
On most tricycle-gear aeroplanes, the main wheels touch first, spin from zero to runway speed and transfer the impact into the tyres, struts and airframe attachments. The shock struts compress in a controlled stroke rather than letting the aircraft bounce freely.
As lift reduces and the aeroplane's weight settles onto the wheels, braking becomes more effective. Weight-on-wheels logic may then permit or command ground functions involving anti-skid, spoilers, thrust reversers and other systems, depending on the aircraft. The pilot lowers the nose wheel gently because it is not designed to receive the primary touchdown load.
During take-off, the gear supports and steers the aeroplane until lift unloads the wheels. Retractable gear is raised after a positive climb is established, reducing drag for the rest of the flight.
When should pilots lower the landing gear?
Pilots lower the gear at the point specified by the aircraft procedure and early enough to confirm a down-and-locked indication before landing. Extension adds substantial drag, so it also helps control speed and establish a stable descent, but extending too early wastes energy and extending too late risks an unstable approach.
Gear movement and flight with the gear extended are limited by published speeds. VLO is the maximum landing-gear operating speed, sometimes with different limits for extension and retraction; VLE is the maximum speed with the gear extended. The aircraft checklist and flight manual remain controlling. Our guide to configuring a visual approach in a flight simulator places the gear selection in the wider approach sequence.
What is the difference between main gear, nose gear and tailwheel gear?
The main gear carries most of the aircraft's weight and landing load, while the nose gear or tailwheel supports the other end and assists with directional control.
On tricycle-gear aircraft, the main legs sit near the centre of gravity and normally contain the wheel brakes. The nose gear supports the forward fuselage and provides low-speed steering, but nose wheels are generally not braked. Rudder control becomes more effective as airflow increases, while nose-wheel steering is most useful at taxi speeds.
A tailwheel aircraft places the centre of gravity behind the main wheels. That arrangement provides good propeller clearance but is less directionally stable on the ground and more prone to a ground loop if a swing is not corrected promptly. It can be landed on the main wheels first or in a three-point attitude; our taildragger take-off and landing techniques for Microsoft Flight Simulator cover those methods in practical detail.
Crosswind drift matters with either arrangement. Touching down while the aircraft is still moving sideways imposes a side load on the tyres and gear; the crab angle itself becomes a problem when it remains at wheel contact. The correct alignment and rollout inputs are explained in our guide to crosswind touchdown and rollout control in a flight simulator.
What are the main types of aeroplane landing gear?
The principal landing gear layouts are tricycle, conventional tailwheel and tandem gear, with floats, skis and skids used for specialised surfaces.
| Type | Arrangement | Typical use and trade-off |
|---|---|---|
| Tricycle | Main gear behind the centre of gravity with a nose wheel | Used by most trainers and airliners. It offers good forward visibility, stable braking and comparatively easy ground handling. |
| Conventional or tailwheel | Main gear ahead of the centre of gravity with a small wheel at the tail | Common on older, aerobatic and bush designs. It provides propeller clearance and can suit rough fields, but demands stronger directional-control technique. |
| Tandem or bicycle | Main units arranged along the fuselage centreline, usually with wingtip outriggers | Suited to certain slender military and specialist aircraft, although the outriggers are needed to prevent the aircraft tipping sideways. |
| Floats, skis or skids | Surface-specific supports replacing or supplementing wheels | Used for water, snow or helicopter operations. They suit a particular operating surface but can restrict ordinary ground handling. |
A bogie or truck is a beam carrying several wheels on one landing-gear leg; it is not a separate whole-aircraft layout. Large aeroplanes use bogies and multiple main legs to spread high loads across more tyres and a greater runway area. Fixed versus retractable is another separate classification: either description concerns movement, not the position of the wheels.
Why are some landing gears fixed and others retractable?
Fixed gear is chosen when simplicity, low weight, durability and easier maintenance matter more than aerodynamic drag; retractable gear is chosen when the performance gain justifies extra complexity.
- Choose fixed gear for simplicity: it suits many trainers, utility aircraft and rough-field machines because there are fewer actuators, doors, locks and warning systems to inspect or fail. Wheel fairings can reduce drag, although mud, snow and surface damage may make fairings undesirable.
- Choose retractable gear for performance: folding the wheels into the wing or fuselage reduces drag, improving climb, cruise speed and fuel efficiency. The penalties are additional weight, maintenance, cost and the possibility of an extension fault or gear-up landing.
At the modest speeds of a basic trainer, permanent gear may be the better engineering trade. On a fast piston aircraft, turboprop or jet, exposed wheels would impose a much larger performance penalty.
How do pilots know the landing gear is down and locked?
Pilots confirm landing gear position through dedicated cockpit indications, warnings and the aircraft's landing checklist. A green indication commonly means down and locked, but colours, symbols and logic differ by type and must never be assumed from another aircraft.
On an aeroplane with three independently indicated legs, three greens means that all three downlock switches report a safe position. Other aircraft use a gear synoptic, text messages or mechanical indicators. An unlit display after electrical power has been removed proves nothing about the physical gear position.
A horn or electronic warning may sound when the aircraft is configured for landing with the gear still up or unsafe. The trigger can involve thrust setting, flap position, radio altitude or other inputs. A faulty switch, wiring problem or mis-rigged sensor can create an unsafe indication even when the leg appears extended, but the gear must still be treated as unsafe until the approved procedure establishes otherwise.
Gear-position switches and weight-on-wheels sensors have different jobs. A leg can be down and locked while the aircraft is flying, while a failed weight-on-wheels sensor can make other systems behave as if the aircraft were still airborne.
What happens if the landing gear will not come down?
If the gear will not extend normally, pilots use the aircraft-specific abnormal checklist and alternate extension system rather than improvising. The general logic is consistent even though the controls and limitations are not.
- Maintain control and observe limits: the crew stabilises the aircraft, remains within the permitted gear speed and identifies which indications disagree.
- Use the approved checklist: this checks the required electrical, hydraulic and control configuration. Randomly cycling the gear can waste remaining hydraulic fluid or move a partly locked leg.
- Operate alternate extension: the checklist may call for an uplock release, free-fall extension, hand pump or backup pressure source.
- Assess the result: cockpit indicators, mechanical tell-tales and system messages are used where fitted. An external observation or tower fly-past can show gross position but cannot necessarily prove that an internal downlock is engaged.
- Prepare for the indicated condition: if the gear remains unsafe, the crew plans the landing, aircraft evacuation considerations and emergency response using the flight manual.
This is an overview of system logic, not a substitute for an aircraft's approved flight manual, pilot's operating handbook or quick-reference handbook.
What can go wrong with an aircraft landing gear system?
Landing gear faults usually involve extension, locking, indication, tyres, brakes, steering or structural overload.
| Problem | Likely causes and effects |
|---|---|
| Unsafe or disagree indication | A leg may be between positions or not fully locked, but a position switch, wiring fault or incorrect rigging can produce the same warning. |
| Failure to extend or retract | Possible causes include lost hydraulic pressure, an electrical fault, failed actuator, jammed door, damaged lock or mechanical obstruction. Shared hydraulic failures may also affect brakes or steering. |
| Tyre damage or blowout | Low pressure, foreign-object damage, excessive heat, a locked-wheel skid or a hard landing can damage a tyre. A skid commonly produces a flat spot before complete failure. |
| Brake fade or overheating | Repeated heavy braking and high-energy stops can reduce performance and damage wheels or tyres. Some transport-aircraft wheels use fusible plugs that release tyre pressure if temperatures become dangerous. |
| Nose-wheel or tailwheel shimmy | Rapid oscillation can result from poor damping, wear, incorrect tyre pressure or alignment problems. Severe shimmy can damage steering and attachment components. |
| Hard-landing or side-load damage | A high sink rate, nose-first touchdown or excessive sideways drift can bend links, overstress attachments or collapse a leg. Damage may exist even when the gear remains standing. |
How do you fix landing gear problems in a flight simulator?
Most apparent simulator landing gear failures come from aircraft state, speed limits, missing system power or conflicting control assignments before they come from a genuine simulated mechanical fault.
- Check what the aircraft should do: fixed gear cannot retract, and many retractable aircraft correctly inhibit retraction while weight-on-wheels logic says they are on the ground.
- Compare the lever, lights and external model: establish whether the command was received, whether the gear is moving and whether only the animation disagrees. A visual model is not reliable proof of a downlock on a detailed add-on.
- Remove conflicting assignments: inspect every connected controller for gear toggle, gear-up and gear-down commands. A latched switch or duplicate binding can immediately reverse a keyboard or cockpit selection.
- Disable unwanted assistance: automated checklists, AI piloting or landing assistance may operate the gear without an obvious manual input.
- Restore the required systems: confirm that electrical power, hydraulic pumps and relevant controls are configured for the aircraft. Do not reset simulated circuit breakers at random if the aircraft documentation models a specific procedure.
- Respect gear speed limits: slow below the published operating limit before trying the checklist action. Some detailed aircraft simulate overspeed damage or prevent an unrealistic gear movement.
- Isolate the fault: if every retractable aircraft is affected, suspect a global control or assistance setting. If only one aircraft is affected, check that model's procedure, saved failure state and system simulation.
A mistake we see constantly is blaming the undercarriage for a poor rollout when the real cause is excessive touchdown drift, an uncalibrated rudder axis, incorrect nose-wheel steering or uneven brake input. Diagnose the cockpit indications and control assignments before treating an external animation or sudden swerve as a mechanical failure.