Landing gear is the system of components that supports the weight of an aircraft and its load while giving it mobility on ground or water. It is the principal support of the airplane when parked, taxiing, taking off, or landing, and it provides structural aircraft load during taxi, takeoff, and landing operations.
This system includes wheels, brakes, shock absorbers, and steering linkages. Wheeled landing gear on small aircraft typically consists of three wheels: two main wheels and a nose wheel or tail wheel. The main components are the main landing gear and the nose gear, or in some configurations, a tail gear. Depending on the design, landing gear incorporates spring struts, oleo struts, or bungee struts to absorb impact forces. It includes aircraft brakes to control movement and steering linkages for directional control on the ground.
Landing gear falls into four main categories, including retractable types that retract into the wings or fuselage during flight. Proper tire servicing and maintenance are vital to guarantee safe and reliable operation.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is an aircraft landing gear?
The landing gear is the principal support of the airplane when parked, taxiing, taking off, or landing, and it consists of three wheels on small aircraft. Airplanes with conventional landing gear are sometimes referred to as tailwheel airplanes, which have a rear mounted wheel and two main wheels located on each side of the fuselage.
Landing gear is the undercarriage of an aircraft that supports the airplane when parked and when taxiing, and it gives the craft mobility on ground. The system takes the form of main undercarriage units that carry most of the load and an auxiliary undercarriage unit located at the nose or tail that carries only a small proportion of the total load and is used for steering purposes.
How important is landing gear to an aircraft?
Landing gear is one of the most important aircraft components. It forms the foundation that enables safe aviation operations from takeoff to touchdown. The structure supports the weight of the craft when the plane is not in flight, during ground operations, and maintains structural integrity throughout thousands of operational cycles covering decades of service. The landing gear system absorbs tremendous impact forces during high speed landings, preventing structural damage to the aircraft, and must be robust enough to handle the stress of both the aircraft's weight and the touchdown shock during landing while providing substantial safety margins. Certification requirements mandate that landing gear structures survive ultimate loads (1.5 times limit load) without failure, guaranteeing safe aircraft landing, takeoff, and taxiing.
Choice of landing gear configuration directly influences aircraft handling characteristics, structural design, maintenance accessibility, weight, reliability, and operational flexibility. Inward-retracting gear impacts weight and maneuverability of the aircraft, whereas retractable undercarriages allow faster airspeeds and smoother flight control, reduce drag, and refine fuel efficiency. A wide stance makes for a more stable take off and landing, yet heavier landing gear reduces payload capacity, illustrating the compromise between ground handling and sky performance. The International Air Transport Association states that the largest proportion of aviation accidents in North America and Europe were caused by landing gear collapses, underscoring why landing gear must be high-quality, reliable, properly inspected and maintained, and operate safely in diverse weather conditions.
I understand the importance of the landing gear in aircraft. Without it, the aircraft cannot takeoff or land safely. Proper functioning of the landing gear is thus crucial to air travel.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
How does a landing gear work?
The landing gear is used for engaging the surface when taxiing, landing, and parking. Retractable landing gear functions with either electrical or hydraulic power. A switch in the cockpit, designed like a wheel, controls the landing gear position.
When the pilot places the gear selector switch in the GEAR DOWN position, the electric motor reverses or hydraulic fluid is directed into the gear-down line. Hydraulic fluid flows through sequenced valves and down-locks to the gear-actuating cylinders. The gear moves down and locks. The lock stay moves to its unfolded position, and mechanical down-locks are operated automatically by the gear retraction system. The whole process of retracting and extending the landing gear is controlled by a computer called LGCIUs, and the cycle completes in about seven seconds.
For retraction, moving the switch to the UP position causes the electric motor to operate or directs hydraulic fluid into the gear-up line. The gear doors open first, the landing gear retracts via hydraulic actuators, and the doors close. The gear retracts and locks, and limit switches de-energize the hydraulic pump after the gear cycle is completed.
Hydraulic landing gear retraction system utilizes pressurized hydraulic fluid to actuate linkages to raise and lower the gear. The pump that pressurizes the fluid is engine-driven or electrically-powered. When an electrically-powered pump is used, the system is called an electro-hydraulic system. Hydraulic pressure holds the gear up, so there are no uplocks on some aircraft.
In an emergency, operating the emergency release handle releases the up-locks and allows the gears to free-fall or extend under their weight. Gravity drop systems release gear uplocks, allowing landing gear to fall into place under its own weight and lock through mechanical downlocks. If the design makes gravity extension impractical, forceful gear extension is required using hydraulic fluid, compressed gas, or a manual hand crank. Hydraulic pressure for emergency operation comes from an auxiliary hand pump, an accumulator, or an electrically powered hydraulic pump.
The landing gear downlock mechanism works like a folding table leg with a 45-degree angled brace and a sliding metal bit that covers its hinge. Electronically operated safety switches prevent accidental operation of the down-locks and inadvertent landing gear retraction while the airplane is on the ground. When the weight of the airplane compresses the strut, the squat switch opens the electrical circuit to the motor or mechanism that powers retraction. Ground locks are pins installed in aligned holes drilled in two or more units of the landing gear support structure to prevent collapse of the gear when the airplane is on the ground.
Pilot confirms that the landing gear has extension and locking by the normal sound and feel of the system operation as well as by the gear position indicators. Landing gear position indicators use a group of three green lights to indicate gear is down and locked, a red or amber light to indicate gear is in transit or unsafe for landing, and silhouette indicators to show when each gear locks in the DOWN position.
Where is the landing gear on an airplane?
The main landing gear is located beneath the aircraft's wings or fuselage. Two main wheels are located on each side of the fuselage. The squat switch is usually mounted in a bracket on one of the main gear shock struts. A squat switch is in either one of the main gears or in the nose.
What are the types of aircraft landing gear?
The types of aircraft landing gear are detailed below.
- Tricycle Landing Gear: The tricycle landing gear configuration features two main wheels situated towards the rear of the aircraft and a single nose wheel at the front. It is used on a wide range of aircraft, from small trainers like the Cessna 172 to large airliners such as the Airbus A320.
- Taildragger Landing Gear: The taildragger configuration features two main wheels towards the front of the aircraft and a smaller wheel at the tail. This gives the aircraft a nose-up stance on the ground, hence the name “taildragger.”
- Tandem Landing Gear: In a tandem landing gear configuration, two sets of wheels are aligned along the centerline of the aircraft, one behind the other. It is found on aircraft like the U-2 spy plane and many gliders.
- Floatplane Landing Gear: Floatplanes feature large floats, or pontoons, in place of traditional wheels. These floats allow the aircraft to take off from and land on water. Floatplanes can be found on the de Havilland Beaver and the Cessna 208 Caravan.
- Ski Landing Gear: Ski-equipped aircraft swap out traditional wheels for skis, enabling them to take off from and land on snow and ice. Most ski-equipped aircraft feature retractable skis around a set of traditional wheels, allowing the aircraft to operate from traditional runways as well.
What is tandem landing gear?
Tandem landing gear is the undercarriage of an aircraft or spacecraft that is used typically on land, but may also be the surface of a water body when parking, taxiing, takeoff or landing. This landing gear configuration is designed for aircraft with a narrow body or fuselage, and it is best suited for aircraft that require a slim profile for aerodynamic efficiency or for fitting into narrow spaces.
In tandem landing gear, known as bicycle landing gear, two sets of wheels are aligned along the centreline of the aircraft, one behind the other. The main wheels are aligned with the aircraft's centreline, and the assemblies are typically retractable. Because the gear is concentrated under the fuselage, the alignment reduces the gear's footprint on the ground and minimizes drag when deployed. Outrigger wheels near the wing tips provide lateral stability, and additional supports include skids. The configuration looks a bit like a unicycle with an extra wheel.
The primary advantage of the tandem landing gear design is its reduced drag when deployed. It is suited for aircraft that require fitting into narrow spaces like a glider. It is mostly used in certain military aircraft and specialized planes that need the capability to land on unprepared or improvised runways. Well-known examples include the Lockheed U-2 spy plane, the Boeing B-52 Stratofortress, the Hawker Siddeley Harrier, and many gliders.
A disadvantage is that it requires careful balancing since the aircraft relies on additional wing-mounted stabilizers or auxiliary wheels to prevent it from tipping over. Tandem aircraft cannot rotate for takeoff, so the forward gear must be long enough to give the wings the correct angle of attack during takeoff. During landing, the forward gear must not touch the runway first, or the rear gear will slam down.
What are the components of landing gear in an aircraft?
The components of landing gear in an aircraft are detailed below.
- Shock Absorbers (Struts): Shock absorbers, or struts, cushion the landing. When the plane touches down, the struts absorb landing impacts, softening the blow. These parts need to be reliable to prevent any harsh jolts for passengers and the aircraft itself.
- Wheels and Tires: They are built to take on high speeds and heavy weight on the runway. Good tires make sure there is a safe landing grip and help reduce any extra drag.
- Brakes: Brakes slow down the plane once it lands. The brakes work best when they are paired with the reverse thrust from the engines to bring the plane to a complete stop.
- Retraction Mechanism: The retraction mechanism is what lets the landing gear move from an extended to a retracted position. When the wheels tuck up after takeoff, it helps the plane fly smoother and faster. During landing, the gear extends, so the wheels are down and locked for touchdown.Steering System: The steering system keeps the plane under control when it is on the ground. It mostly works with the nose gear, which helps direct the plane on runways and taxiways.
