Definition

On modern sophisticated aircraft, autobrake systems provide braking action automatically upon landing or in the event of a rejected takeoff.

Description

Autobrake systems are integrated with wheel spin-up sensors, thrust levers, and other aircraft components. When armed, the system can detect either a rejected takeoff or a landing touchdown. Settings for the Embraer 170/190 provide a typical example: Switch positions are labeled RTO, OFF, HI, MED, LO. The HI, MED, and LO positions represent selectable deceleration rates. RTO arms the system to decelerate the aircraft in the event of a rejected takeoff.

In most systems, autobrakes will engage upon landing if:

• The system is armed.
• The main wheels spin up.
• The thrust levers are at idle.

Typically, once armed, the autobrakes can be disarmed by pressing the toe brakes or by advancing the throttles for a rejected landing.

Depending on the aircraft and on operator policy, autobrake usage can be mandatory or optional. Some emergency procedures in a given aircraft's Quick Reference Handbook (QRH) may require maximum manual braking rather than autobrake usage.