Braking is one of the vital functions of an aircraft. In an emergency it should be possible to stop an aircraft of several hundred tons in the shortest minimum time and distance. The maximum take-off weight of an A380 is 575 metric tonnes, that of a Boeing 747-8 is 448 (one metric tonne = 2,204.62262 lb).
This requires that the brakes should be capable of absorbing very high temperatures in excess of, or equal to, 1,000°C (1,800°F ), according to information provided by Messier-Bugatti-Dowty (Safran group). The brakes of a Formula 1 can absorb the same level of temperature. To reduce the brake temperatures before taking-off again, there are brake cooling fans on some aircraft.
Today, carbon is the best material for a high performance brake system necessitating the absorption of a great deal of energy. Whereas two brake pads are sufficient to stop a car, an airplane uses multiple stacked disc assemblies.
Compared with steel brake discs that equipped commercial and military aircraft previously, carbon has several advantages in terms of performance: considerable weight saving ( half that of steel ) and endurance ( the durability of a carbon disc is twice that of a steel one ). Moreover, carbon is not only insensitive to thermal shock, but also mechanical fatigue. As for the price of a carbon disc, it is similar to that in steel.
With aviation’s increasing use of electricity, hydraulic brakes are being replaced progressively by electrical systems.