What you should know about…aircraft brakes
All modern commercial aircraft have automatic brake systems. Just like a car, these systems also have an anti-lock braking system (ABS) that prevents the tires from sliding down a wet runway. The advantage of the automatic brake system is that the aircraft brakes comfortably at a constant deceleration. Passengers experience a constant force that presses them into their seats. The brake system automatically applies the wheel brakes just enough to create a constant deceleration independent of the air resistance, spoilers and reversers. It is only in the last phase of braking, known as the rollout, that the pilot takes over the wheel brakes by pressing on both brake pedals. This deactivates the automatic brake system. Immediately after landing, the aircraft is still moving fast enough that aerodynamic devices are much more efficient than the brakes.
The Airbus A320 while landing: from 155 mph (250 km/h) to a complete stop
The effective weight of an Airbus A320 upon landing is about 58 metric tons. The aircraft lands on the runway at a speed of about 155 mph (250 km/h). To extend brake flaps, the pilot must first activate the system. The brake flaps are extended as soon as a weight of at least 6,300 kg is placed on the two rear landing gears. This is followed by thrust reversal. The actual wheel brakes are used as the third brake system. Only the main landing gears brake as a rule. The wheel brakes are activated once the rear wheels reach a speed of about 85 mph (140 km/h). A brake must be warmed up to operate well. To reach a temperature of about 200°C (392°F), the aircraft first rolls with the brakes applied slightly and only then are they applied fully.
Steel or carbon brakes: What is the difference?
Steel brakes were used for years as standard in the aviation sector. Since the 1980s, they are being replaced more and more with carbon brakes. Steel brakes are relatively heavy and can only withstand temperatures up to 2,000°C (3,600°F). They must be replaced after an average of 1,000 landings.
Carbon brakes have become the standard on newer aircraft in the meantime. They are considerably lighter than steel brakes. For a B737, this translates into 320 kg less weight and thus less kerosene is needed. Carbon brakes are much more sturdy, having the ability to withstand temperatures of up to 3,000°C (5,400°F). Even the service life is longer. Carbon brakes can handle 2,000 landings on average. This results in longer service intervals and lower maintenance costs. But, carbon brakes are more expensive than steel brakes.
| Aircraft type | Steel brake [kg/lbs] |
Carbon brake [kg/lbs] |
Weight savings per aircraft [kg/lbs] |
|---|---|---|---|
| B747 - 400 | - | 107 / 236 | - |
| B757 | 101/223 | 60/132 | 328/723 |
| B767 | 141/311 | 89/196 | 416/917 |
| B777 | - | 103/227 | - |
| A300 | 145/320 | 75/165 | 560/1230 |
| A310 | 132/291 | 74/163 | 464/1023 |
| A320 | - | 66/146 | - |
| A380 | - | 110/243 | - |
Table: Difference in weight between steel brakes and carbon brakes for different aircraft models
The next generation of brakes: activated electromechanically instead of pneumatically
The Boeing B787 Dreamliner is the first commercial passenger aircraft to use electrically activated brakes instead of hydraulically activated ones. A system used in military aircraft since 1998 moved into the first airliner in 2011. Depending on the aircraft model, the electromechanically activated brakes replace several kilometers of hydraulic lines with cables. As a result, hydraulic fluid is no longer used anywhere in the entire brake system. This is considerably easier to maintain and compatible with the environment. Possible leaks are completely eliminated.
What do brakes cost?
After roughly 1,000 – 2,000 landings, the brakes need to go to the brake shop for a check. A pin located inside the brakes serves as an indicator of brake wear. The price for one brake differs depending on the aircraft model. For example, the list price for a Boeing 777 is approximately 100,000 USD for a complete 12-piece brake set. Four large brake manufacturers share of the market. These are Messier-Bugatti-Dowty, Goodrich, Meggitt Aircraft Braking Systems and Honeywell Aerospace.
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