Autobrake

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An autobrake is a type of automatic wheel-based hydraulic brake system for advanced airplanes. The autobrake is normally enabled during takeoff and landing procedures, when the aircraft's brake system can be handled by the automated systems of the aircraft itself in order to keep the pilot free to perform other tasks.

[edit] Landing

When in a landing scenario, the autobrake can aid in freeing up the pilot to allow him or her to monitor other systems (such as the execution of the landing flare). There are usually several settings for the "intensity," or hydraulic pressure of the brake mechanism. These settings are numbered, with "1" referring to braking for a light speed reduction, and subsequent numbers referring to more abrupt speed reductions.

When the landing feature of the autobrake is engaged, the aircraft automatically engages pressurized wheel braking upon touchdown to the landing surface (usually a runway).

One of the main advantages of engaging the autobrake as opposed to manually pressing on brake pedals is the uniform deceleration mechanism of the autobrake. The aircraft automatically decelerates at the selected level regardless of other factors, such as aircraft drag and other deceleration methods (such as deployment of thrust reversers or spoilers).

[edit] Rejected Takeoff

When taking off, the aircraft's autobrake can be set to the rejected takeoff mode, commonly indicated on an aircraft panel as RTO. In RTO setting, the aircraft monitors certain variables, depending on the autobrake model. Most autobrakes engage RTO braking if the pilot returns the throttle to the "idle" position, or if reverse thrust is engaged. Other autobrake systems may monitor critical flight controls for failures.

The autobrake is designed to only trigger RTO braking if it is traveling at speeds less than V₁, the maximum speed at which it is possible to stop the aircraft on the ground in the event of a critical failure.