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Auto Thrust vs Auto Throttle

If you’re seeking to understand the distinction between auto thrust and auto throttle, your initial query might be incomplete. You may be interested in whether it pertains to the movement of throttle or thrust levers.

Understanding the word Throttle First!

Starting with “throttle,” technically, it refers to a device that regulates airflow by constraining an air intake passage. This method of managing engine output is typical in piston engines. Whether employing a carburetor or a fuel control unit, the primary mechanism involves controlling air intake to regulate output in piston engines.

Power/Thrust for Turboprop and Turbojet engines.

In turbine engines, output is managed by modulating the fuel supply since the geometric exposure to air intake remains relatively constant. Therefore, the term “throttle” is inappropriate in this context and is only applicable to piston engines. For turbine engines, including turboprop engines, the correct terminology is “thrust lever” or “power lever” respectively.

A system that automatically regulates engine output based on the demand generated by any type of flight automation system is referred to as either auto throttle or auto thrust, depending on the specific context and terminology used.

Boeing – Auto throttle/ Airbus – Auto thrust

Boeing and several other aircraft manufacturers commonly use the term “auto throttle,” while Airbus more precisely refers to their system as “auto thrust” since it directly controls the thrust output.

Concept of thrust/power lever movement (Auto throttle or Auto thrust – Which is better?)

The movement of thrust/power levers isn’t determined by nomenclature; rather, it reflects the design philosophy of the manufacturer. This aspect is subject to debate, as each approach carries its own set of advantages and disadvantages.

Airbus Pilot’s point of view:

From an Airbus pilot’s perspective, monitoring the Primary Flight Display (PFD) is crucial. If the speed trend indicator drops toward the lower end of the speed bug, the expectation is for thrust to increase. A quick glance at the N1 or EPR gauges confirms the engines are winding up. This visual cue is preferred over tactile feedback since the movement of thrust levers on a Boeing doesn’t necessarily guarantee engine response. In essence, relying on instrument readings ensures a more accurate assessment of engine behavior.

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