ANSWERS: 5
  • With the brake pedal as on an auto. The engines on most jets have a device to move and cause the engine thrust to be diverted back toward the front of the jet causing the jet to slow down.
  • There are two different types of braking systems on a typical commercial jetand both are controlled hydraulically. One being the toe brakes. These are activated by pressing on the top part of the rudder pedals together and the other are the thrust reversers on the aft end of the engines. Think of an opened clamshell. The engine's thrust hits the base of the clam shell and is deflected forawrd in the direction the aircraft is travelling when it touches down. Both are used on landing. First the thrust reversers, then when ground speed has been bled off enough, the toe brakes are used.
  • In addition to what scubabob said there are also flaps on top of the wings called spoilers. Spoilers extend on touchdown and increase wind resistance. They also decrease lift to give the toe brakes better traction.
  • Many airliners are also equipped with computer-controlled auto-brakes. The system can be selected to apply brakes with different levels of force depending on the landing weight of the aircraft and the length of the runway.
  • Jet airliners have multiple systems of braking, often used in coordination with one another. Jets typically have three basic types of brakes. Hydraulic brakes are only used on the ground, whether applied by toe pedals or an automatic setting. The second type of brakes are the thrust reversers (abreviated TR), used in the air on some jet models but normally on the ground. The third type of brake are those that add drag to the plane by airflow disturbance. These are called spoilers or speed brakes. (if you prefer Boeing's name for it) All planes also have parking brakes, but a discussion of these is for a different question. You may be wondering why I am elaborating so much here, but this is actually quite interesting. These braking systems don't just take place on the ground, they are often used while airborne, with the exception of the hydraulic wheel brakes which would do no good in the air. The spoilers are rectangular panels located on the top of the wing which spring up to disturb the airflow, killing airspeed and lift while adding drag. These can be used for fast descents while in flight. Smaller movements of the spoilers are coordinated with the flight control systems on many commercial airliners. When you apply aileron inputs, spoilers assist in the roll. During the pre-landing checks, the spoilers are set to the "armed" position. This means that the moment the rear wheels touch the runway the spoilers will spring up to kill lift and assist in the completion of the landing. Also note that wing flap settings also serve as brakes in this same way. They add drag to the plane by trailing behind the wings. In coordination with spoiler settings, pilots also analyze braking conditions at the destination airport. This is how they determine the level of hydraulic pressure to set for the autobraking system. If conditions are slick and braking is expected to be bad, a lighter pressure setting is used. If the plane is landing on a 15,000 foot runway, no setting is needed. This autobrake setting can also be turned to manual or "auto," which will enable either the pilot or computer to determine how much to apply. Should the pilot apply the brakes with his feet, this is done by pushing on the top of both rudder pedals at the same time, known as toe braking. Lastly, I will make a short mention of the thrust reverse. This is used in coordination with an autobrake setting and an armed speed brake during landing. Imagine that the rear of the engine is hinged and can open up to deflect the thrust into a different direction. In a commercial jet's landing procedure it usually states that these should be deployed after all wheels are on the ground. They are usually disengaged when airspeed drops to 80 knots. Some aircraft have a type of TR that can be deployed in flight. It produces a similar result to the spoilers, adding drag and reducing lift. Some four engine jets are only equipped with two TR's instead of four. A great example of this is the new Airbus A380.

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