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Throttle Actuator

Technical Information

Catalogue No: PC00065
Picture Type: Rochester Photo Negative
Topic: Flight Control
Title: Throttle Actuator
Date: 16 Jun 1964
Width (mm): 127
Height (mm): 102
Copies: 1
Location: Negatives Cabinet PC ("C" Negs) [RAA Office]

An autothrottle (automatic throttle, also known as autothrust, A/T) is a system that allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling the fuel flow. The autothrottle can greatly reduce the pilots' workload and help conserve fuel and extend engine life by metering the precise amount of fuel required to attain a specific target indicated air speed, or the assigned power for different phases of flight. Autothrottle and AFDS (Auto Flight Director Systems) can work together to fulfill the whole flight plan.

There are two parameters that an Autothrottle can maintain or try to attain: speed and thrust.

In speed mode the throttle is positioned to attain a set target speed. This mode controls aircraft speed within safe operating margins. For example, if the pilot selects a target speed which is slower than stall speed, or a speed faster than maximum speed, the autothrottle system will maintain a speed closest to the target speed that is within the range of safe speeds.

In the thrust mode the engine is maintained at a fixed power setting according to the different flight phases. For example, during takeoff, the Autothrottle maintains constant takeoff power until takeoff mode is finished. During climb, the Autothrottle maintains constant climb power; in descent, the A/T reduces the setting to the idle position, and so on. When the Autothrottle is working in thrust mode, speed is controlled by pitch (or the control column), and not by the Autothrottle. A radar altimeter feeds data to the Autothrottle mostly in this mode.

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