The International Air Transport Association or IATA (2024) states in its 2023 Annual Safety Report that the largest proportion of aviation accidents in North America and Europe were caused by landing gear collapses. This shows that the aircraft landing gear, a seemingly simple yet important component, is essential for safe aircraft landing, takeoff, and maneuvering. From its role in supporting the aircraft's weight to its shock-absorbing capabilities, the landing gear is a testament to engineering ingenuity.
Key Takeaways
- The landing gear system is crucial for aircraft stability, control, and safety in takeoff, landing, and ground operations, making it an indispensable part of aviation.
- Different types of landing gear configurations, such as conventional, multi-wheel, and ski landing gear, serve specific purposes and are tailored to various aircraft and operational needs.
- Key parts, including shock absorbers, brakes, and actuators, each play unique roles in managing impact forces, ensuring stability, and allowing controlled maneuvering on the ground.
- Landing gear failures stem from various factors, including mechanical issues, human error, and environmental conditions.
- Routine inspections, component upgrades, and predictive maintenance technology are essential for minimizing risks, extending the lifespan of aircraft landing gear, and enhancing overall safety.
What Is Landing Gear?
Aircraft landing gear is a complex system composed of structural parts, hydraulics, energy-absorbing components, brakes, wheels, and tires. Additional components such as steering devices and retraction mechanisms may also be integrated. The primary function of landing gear is to mitigate the impact of landing by absorbing and dissipating kinetic energy.
Types of Landing Gear
The different types of landing gear vary by design and configuration. Each serves a specific purpose depending on the aircraft and its function in the industry.
Types of Landing Gear by Design
The design of an aircraft's landing gear significantly impacts its performance and operational capabilities. Let us look at the two primary types of landing gear, fixed and retractable, highlighting their unique features and suitability for different aircraft types.
Fixed Landing Gear
Fixed Landing Gear is a type of landing gear that remains extended at all times such as the one shown in image (a) above.
- Applications: This gear is primarily found on lighter aircraft, trainers, and some utility planes.
- Advantages: The design provides a straightforward and durable option for supporting the aircraft during takeoff, landing, and taxiing. It involves fewer moving parts, making it less complex and often less costly to maintain.
- Disadvantages: Because the gear stays extended throughout the flight, it creates significant aerodynamic drag. This forces the aircraft to consume more fuel to maintain speed and altitude.
Retractable Landing Gear
Retractable systems allow the landing gear to be drawn into the aircraft’s fuselage or wings once the plane is airborne. The image (b) above shows a retractable landing gear in a commercial airplane.
- Applications: Retractable Landing Gear has become the standard in most modern commercial and military aircraft.
- Advantages: By retracting the gear, the aircraft experiences less air resistance directly, boosting fuel efficiency and allowing for higher speeds.
- Disadvantages: Retractable landing gear systems are more complex and heavier than fixed landing gear, reducing payload capacity. The mechanical and hydraulic systems involved in retracting and extending this type can be prone to failures requiring more maintenance. Pilots must also follow flying protocols operating retractable landing gears increasing potential errors.
Types of Landing Gear by Configuration
Landing gear configurations differ with each aircraft’s needs. Each arrangement is designed to support specific types of landings and operations.
Conventional Landing Gear (Tailwheel Configuration)
Often referred to as “taildragger” gear, this configuration features two larger main wheels positioned at the front of the aircraft and a smaller wheel or skid near the tail. Note the landing gear near the plane’s tail in the image (a) above.
- Applications: This setup was common in older aircraft and is still found on smaller planes and bush aircraft.
- Advantages: Tailwheel gear enables the aircraft to handle uneven or rugged runways better than other configurations.
- Disadvantages: However, it requires careful handling as it tends to “ground loop,” where the plane pivots uncontrollably around the main wheels if not managed properly.
Multi-Wheel Landing Gear
Multi-wheel landing gear includes multiple wheels arranged in sets or bogies, allowing the load to spread across several contact points. The image (b) above demonstrates this type of gear. Examples are the tricycle and quadricycle landing gears. The image above shows a multi-wheel landing gear arranged in bogies.
- Applications: This configuration is designed for heavy, large aircraft, such as commercial airliners and cargo planes.
- Advantages: This distribution reduces stress on individual tires extending their lifespan and reducing maintenance costs. It also improves stability during taxiing and takeoff, especially on wide-body jets or aircraft carrying heavy loads. Multi-wheel setups can also better handle emergencies or uneven runway surfaces.
- Disadvantages: The additional weight of the extra wheels and supporting structures can reduce payload capacity and fuel efficiency. The complexity and weight of multi-wheel landing gear systems increase manufacturing and maintenance costs. In some cases, the increased number of wheels can reduce ground clearance, limiting the aircraft's ability to operate on rough terrain or soft ground.
Tandem Landing Gear
This type has its wheels aligned along the aircraft’s centerline, typically in pairs running from the front to the rear. Note the outliers or landing gears near the aircraft's wings in the image (c) above.
- Applications: Tandem landing gear is mostly used in certain military aircraft and specialized planes that need the capability to land on unprepared or improvised runways.
- Advantages: The tandem alignment reduces the gear’s footprint on the ground.
- Disadvantages: It requires careful balancing since the aircraft relies on additional wing-mounted stabilizers or auxiliary wheels to prevent it from tipping over. This configuration demands a high level of piloting.
Ski Landing Gear
Ski landing gear is designed for aircraft with skis instead of wheels as shown in the image (d) of the plane above. This setup features skis that allow the aircraft to land smoothly on frozen or snow-covered surfaces as seen in the image above.
- Applications: Ski gear is essential for scientific missions, emergency services, and other operations.
- Advantages: The skis are often retractable or interchangeable with wheels, giving pilots the flexibility to operate on both snow and regular runways. It is useful in extreme environments where traditional wheeled gears would sink into soft snow or become bogged down.
- Disadvantages: Ski landing gear restricts aircraft operations to snow-covered surfaces, limiting their versatility. Landing on icy surfaces with ski gear also requires careful control, as reduced friction can affect braking and steering.
Landing Gear System Components
An effective landing gear system is far more complex than a set of wheels. This system supports the aircraft and its load at a Factor of Safety (FoS) of 4.0 to 6.0 and above. Each component has a specific purpose that contributes to the overall safety of aircraft operations.
Main Landing Gear
- Strut: The primary shock-absorbing component, usually a hydraulic or pneumatic system, which absorbs the impact of landing and provides support during taxiing.
- Wheels: These are typically made of high-strength materials like titanium or steel and are designed to withstand high forces during landing and taxiing.
- Tires: Specialized tires can handle aircraft weight and the forces during landing and takeoff. These are typically inflatable, with strong treads for better runway grip.
- Brakes: Hydraulic or electric systems connected to the wheels provide stopping power during landing or taxiing.
Nose Landing Gear
- Strut: Similar to the main gear strut, it absorbs the impact during landing and supports the aircraft on the ground.
- Wheel(s): Generally smaller than the main gear wheels, these support the nose of the aircraft.
- Steering Mechanism: The nose gear often includes a steering mechanism typically controlled by the pilot through the rudder pedals or tiller during taxiing.
Other Components
- Shock Absorbers: These are designed to absorb the impact forces generated during landing, preventing excessive stress on the aircraft's structure. This system typically consists of hydraulic or pneumatic components that work in tandem to dampen the shock.
- Leg (Gear Leg): The leg, or gear leg, is the vertical structure that connects the wheel and tire assembly to the aircraft's fuselage or wing. This houses the shock absorber system, withstands aircraft weight, and provides stability during taxiing and takeoff.
- Retract/Extend Mechanism: The retract/extend mechanism moves the landing gear in and out of the retracted position. They consist of hydraulic actuators or electric motors.
- Fairings and Doors: When the landing gear is retracted, these components cover and protect the gear from environmental factors such as rain, snow, and debris. Fairings and doors also contribute to the aircraft's aerodynamic efficiency by reducing drag.
- Anti-Skid System: An anti-skid system is a safety feature designed to prevent wheel lockup during braking, which can lead to loss of control and skidding. This system continuously monitors wheel rotation speed and automatically adjusts brake pressure to maintain optimal braking performance.
How a Landing Gear Works
Landing gear systems operate and require careful control to handle the forces involved in takeoff, landing, and ground movement.
Aircraft Takeoff
During takeoff, the landing gear supports the aircraft and ensures a smooth departure. Here's how it works:
- Ground Roll: The landing gear supports the aircraft's weight on the ground and provides traction for takeoff. The tires grip the runway surface, allowing the aircraft to gain speed.
- Retraction: Once the aircraft reaches a safe takeoff speed and lifts off the ground, the landing gear retracts within the wings or fuselage using hydraulic systems.
- Reduced Drag: Retracting the landing gear significantly reduces aerodynamic drag, allowing the aircraft to climb more efficiently and reach its cruising altitude faster.
- Improved Aerodynamics: With the landing gear retracted, the aircraft's streamlined shape reduces air resistance, improving its overall performance and fuel efficiency.
Aircraft Landing
During landing, the landing gear absorbs the shock upon impact preventing any structural damage to the aircraft. Here's a breakdown of how it works:
- Deployment: As the aircraft approaches the runway, the pilot deploys the aircraft landing gear. This is typically done by hydraulic systems, which extend the gear from its retracted position within the wings or fuselage.
- Impact Absorption: Upon touchdown, the landing gear's shock absorption system absorbs the impact of the landing, preventing excessive forces from being transferred to the aircraft's structure.
Aircraft Ground Maneuvering
The landing gear is crucial for an aircraft's ground maneuvering. It provides the necessary support and control for taxiing. Here's a breakdown of its role:
- Support: The landing gear bears the aircraft’s weight allowing it to move on the ground.
- Steering: The nose wheel or tail wheel (depending on the aircraft type) is steerable, enabling the pilot to direct the aircraft's movement.
- Braking: The wheel brakes provide the necessary braking force to slow down or stop the aircraft.
Common Landing Gear Failures and Safety Concerns
Despite advances in technology, landing gear failures can still occur. Each potential failure type brings unique risks and understanding them is essential for anyone in aviation safety.
- Mechanical Failures: Mechanical failures in landing gear systems can stem from malfunctions in actuators, locking mechanisms, or shock absorbers. Any weakness in the structure, whether from prolonged wear and tear or lack of maintenance and repair, can lead to landing gear failure at critical moments.
- Environmental Factors: Extreme temperatures can cause thermal stress and affect hydraulic fluid performance. Moisture and corrosion can also degrade components and reduce system efficiency. Additionally, foreign object debris and extreme weather conditions can increase the risk of landing gear failure.
- Human Error: A simple oversight, such as forgetting to extend the landing gear before descent, can lead to catastrophic outcomes, including forced emergency landings.
Real-world incidents involving landing gear failures underscore the critical nature of this system and the severe consequences when issues arise.
A case of landing gear malfunction is the United Airlines Boeing Jet 757-200 last June 2024. This plane lost its main landing gear wheel while flying 174 passengers from Los Angeles International Airport to Denver International Airport. While no passenger was injured, this incident triggered a federal safety review after another similar incident of United Airline landing gear wheel malfunction last March 2024.
Preventive Measures for Landing Gear Safety
Safety around landing gear isn’t just about technology. It’s about proactive measures and regular training. Here are some of my recommendations on how to reduce the risk of incidents.
- Routine Inspections: Frequent checks on tires, hydraulic fluid levels, actuators, and other components are crucial to identify wear or potential issues early. A consistent inspection routine can catch small issues before they become major problems.
- Component Upgrades: Landing gear technology is always advancing. Upgrading components to ensure they meet the Code of Federal Regulations on design and construction for Aircraft Airworthiness Standards improves durability and reduces the risk of failure.
- Predictive Maintenance Technology: With data-driven insights, predictive maintenance helps identify issues before they happen. By analyzing real-time data from landing gear components, maintenance teams can forecast potential problems, minimizing unscheduled repairs.
- Training for Aircraft Personnel: For aviation personnel, understanding the Federal Aviation Administration (FAA) landing gear functions and procedures is essential. Regular training on emergency protocols and operations helps staff prepare for unexpected issues and ensures they know how to respond if things go wrong.
Recent years have seen a renewed focus on landing gear safety, with several advancements and best practices emerging. Airlines are increasingly investing in advanced inspection techniques like smart sensors and predictive maintenance to proactively identify and address potential issues.
Frequently Asked Questions
How does an aircraft landing gear work?
The aircraft landing gear provides essential support for the plane during ground operations, absorbs the force of impact during landing, and enables precise steering for taxiing. Hydraulic or electric actuators manage the extension and retraction of the landing gear, allowing it to be deployed during takeoff and landing and stowed away during flight. Shock absorbers within the gear system cushion landings, reducing stress on the airframe and enhancing passenger comfort.
Can a plane fly with its landing gear out?
Yes, a plane can technically fly with its landing gear extended, but it’s not ideal. Flying with the gear out increases drag significantly, causing the plane to use more fuel and reducing its overall speed and efficiency. For this reason, the retractable landing gear is standard in most modern aircraft, allowing the gear to be tucked away once the plane is airborne.
Can pilots land without landing gear?
In emergencies, pilots may execute a “belly landing” if the landing gear fails to deploy. This technique, though risky, involves landing the aircraft on its fuselage to bring it to a stop as safely as possible. Pilots are trained in these emergency procedures, which prioritize passenger safety and minimize potential damage.
What happens if a plane's landing gear doesn't work?
If the gear malfunctions, pilots may attempt alternative methods to deploy it, such as using a backup hydraulic system or manual release mechanisms. If these options fail, pilots will prepare for an emergency landing, which could involve landing with the aircraft landing partially or fully retracted.
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