|
An autothrottle (automatic throttle) allows a pilot to control the power setting of an aircraft's engines automatically. This helps conserve fuel and engine life by metering a precise amount of fuel to attain (usually) a specific target indicated air speed. There are two parameters that an A/T (autothrottle) can maintain, or try to attain: Speed and Thrust. In Speed mode, A/T, without going beyond its limitation, moves the throttle to a position to attain the target speed, meanwhile to protect the speed within the aircraft safety margin. For example, if the pilot selects a target speed which is slower than stall speed, or a speed that is faster than maximum speed, the A/T will maintain a speed that is within the safety region though to the most extend to close to the target speed. In another word, when the A/T is in the Speed mode, speed is protected, and maintained to the target speed provided the target speed is a reasonable one. In Thrust mode, A/T, disregarding speed, maintains a fixed power setting according to the different flight phrases. For example, during takeoff, A/T maintains a constant takeoff power till the takeoff mode is finished. During climb, A/T maintains a constant climb power; Descend, A/T retard throttle to IDLE position, etc. When A/T is working in Thrust mode, the speed is controlled by pitch (or control collum), and NOT protected by A/T. On Boeing type aircraft, A/T is able to work the whole flight phrases from takeoff, climb out, cruise, descent, approach, all the way to landing or go around. Mode selection is automatic without the need of any manual selection unless interrupted by pilots.
Origins A primitive autothrottle was first fitted to later versions of the Messerschmitt 262 jet fighter late in World War II. Nowadays it is often linked to a Flight Management System, and FADEC is an extension of the concept to control many other parameters besides fuel flow. | ||||||||
|
| |||||||||
 |
|
| |