What you should know about…Landing-gear
Touchdown. An A380 has just landed safely at FRA. One of the unsung heroes? The landing gear, which had to absorb a landing weight of up to 391 metric tons. Just another day in the life of an indispensable aircraft component.
In addition to the nose landing gear, there’s a huge variety of main landing gear systems with a huge variety of axles out there. So what exactly determines which one needs to be used? The aircraft’s size and, especially, its maximum takeoff weight. In the case of the Airbus A380, the main landing gear is subdivided into the body landing gear (BLG) and wing landing gear (WLG).
By the end of World War II, all aircraft was equipped with conventional landing gear, also known as tailwheel-type landing gear. This system features two landing gear struts near the center of gravity, as well as a tailskid or tailwheel at the back of aircraft. However, conventional landing gear has since lost out to tricycle landing gear in virtually all aircraft, which has resulted in an enormous advantage for pilots: much better visibility during takeoff.
The undercarriage arrangement often makes it possible to determine which aircraft model is involved
Rarities such as the Antonov AN-225 cargo aircraft feature two nose landing gears, but most aircraft feature just one. This is just one example of how an undercarriage arrangement, together with the number of axles, can make it possible to determine which aircraft model is involved without the need for any other information.
6 wheels, [1x2] + [2x2]
10 wheels, [1x2] + [2x4]
12 wheels, [1x2] + [2x4 + 1x2]
14 wheels, [1x2] + [3x4]
22 wheels, [1x2] + [2x4 + 2x6]
18 wheels, [1x2] + [4x4]
14 wheels, [1x2] + [2x6]
8 wheels, [2x2] + [2x2]
32 wheels, [2x2] + [2x14]
Landing gear in detail
Landing gears are a relatively heavy aircraft part, and can actually account for up to 7% of the maximum takeoff weight. So what is its main task? And which parts are involved?
The landing gear not only supports the aircraft on the ground, but also makes it possible for the aircraft to move forward on the ground with wheels, tires, and brakes. Moreover, it’s designed to enable the aircraft to reach the required speed for takeoff. Meanwhile, when it comes to landing, the landing gear absorbs the relatively large impact loads that are produced and keeps them from reaching the airframe. In this case, however, it’s the shock absorbers that do the work. In fact, the shock absorption provided by the struts also helps lessen bounce after a sharp touchdown. A variety of valves are used for maintenance and filling with operating fluids such as gas and hydraulic fluid. Finally, wheel brakes are used to shorten landing runs, abort takeoffs, control speed, and as a parking brake on the ground.
Picture: Entire landing gear set for a B747-8
So what happens if the landing gear fails to extend?
The landing gear is extended somewhere between 15 and 8 kilometers before the runway, with the actual distance depending on the specific aircraft model. If we convert that to time units, we’re talking around two to four minutes before touchdown. So what if things don’t work? Well, if the landing gear still fails to extend after a second attempt, which is referred to as “recycling” the landing gear, there’s still one more option: the “gravity drop emergency extension system.” This system consists of a red lever in the cockpit that the pilot needs to extend and turn. Once this happens, the landing gear will drop from the bay properly and lock into place, ensuring that landing can proceed normally.
Landing gear manufacturers
Three manufacturers dominate the landing gear market. The industry leader is Safran Landing Systems (formerly Messier-Bugatti-Dowty), a landing gear manufacturer that is the world’s largest supplier when it comes to landing gear system design, development, production, and support. Another supplier is UTC Aerospace Systems (formerly the Goodrich Corporation), which supplies, among other things, landing gear for the A380. Finally, a German supplier is e.g. Liebherr Aerospace.
Landing gear maintenance
Before every single takeoff, mechanics and pilots visually inspect all landing gear, including the tires and brakes, in what is referred to as a “pre-flight check.” Moreover, every aircraft needs to undergo a D check after several flight months. During this check, the landing gear is checked inside out and fully overhauled, which in the case of an Airbus A340 can involve up to 10,000 individual parts.
Removing landing gear requires special tools, going from winches and tools typical for the aircraft, through trolleys for holding and positioning the landing gear underneath the aircraft, all the way to dollies. Our equipment for the landing gear change includes all applications, covering removal / installation or transportation of a landing gear as well as for wheel and brake change applications.
It’s worth mentioning that meticulous maintenance and overhauling are not just relevant to safety, but also pay off for themselves: The entire landing gear set for an A340 weighs about six metric tons and costs up to six million euros when new, and that’s without counting the brakes and wheels. Repairs are immensely cheaper.
Here you can find more information on our landing gear change equipment: