An autothrottle (automatic

throttle A throttle is a mechanism by which fluid flow is managed by construction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ha ...

; also known as autothrust, A/T, or A/THR) is a system that allows a

pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...

to control the power setting of an

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

engines An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...

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 A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

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. A/T and AFDS (Auto Flight Director Systems) can work together to fulfill the whole flight plan.

Working modes

There are two parameters that an A/T can maintain, or try to attain:

speed In kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a non-negative scalar quantity. Intro ...

and

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

. In speed mode the throttle is positioned to attain a set target speed, subject to safe operating margins. For example, if the pilot selects a target speed which is slower than

stall speed In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack exceeds its critical value.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 486. Aviation Supplies & Academics, 1997. ...

, the autothrottle system maintains a speed above the stall speed. In the thrust mode the engine is maintained at a fixed power setting according to the different flight phases. For example, during

takeoff Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff. For aircraft that take off horizontally, this usually involves starting with a tr ...

, the A/T maintains constant takeoff power until takeoff mode is finished. During climb, the A/T maintains constant climb power; in descent, the A/T reduces the setting to the idle position, and so on. When the A/T is working in thrust mode, speed is controlled by pitch (or the control column), and not by the A/T. A

radar altimeter A radar altimeter (RA), also called a radio altimeter (RALT), electronic altimeter, reflection altimeter, or low-range radio altimeter (LRRA), measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it t ...

feeds data to the autothrottle in this mode.

Usage

Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...

-type aircraft, A/T can be used in all flight phases from

, climb, cruise, descent,

approach Approach may refer to: Aviation *Visual approach *Instrument approach * Final approach Music * ''Approach'' (album), by Von Hertzen Brothers * ''The Approach'', an album by I:Scintilla Other uses *Approach Beach, a gazetted beach in Ting Kau, H ...

, all the way to

land Land, also known as dry land, ground, or earth, is the solid terrestrial surface of Earth not submerged by the ocean or another body of water. It makes up 29.2% of Earth's surface and includes all continents and islands. Earth's land sur ...

go-around In aviation, a go-around is an aborted landing of an aircraft that is on Final_approach_(aeronautics), final approach or has already touched down. A go-around can either be initiated by the pilot flying or requested by air traffic control for var ...

, barring malfunction.

Taxi A taxi, also known as a taxicab or simply a cab, is a type of vehicle for hire with a Driving, driver, used by a single passenger or small group of passengers, often for a non-shared ride. A taxicab conveys passengers between locations of thei ...

is not considered a part of flight, and A/T does not work for taxiing. In most cases, A/T mode selection is automatic without the need of any manual selection unless interrupted by pilots. According to Boeing-published flight procedures, A/T is engaged before the takeoff procedure and is automatically disconnected two seconds after landing. During flight, manual override of A/T is always available. A release of manual override allows A/T to regain control, and the throttle will go back to the A/T commanded position except for two modes (Boeing type aircraft): IDLE and THR HLD. In these two modes, the throttle will remain at the manual commanded position.

History

A primitive autothrottle was first fitted to later versions of the

Messerschmitt Me 262 The Messerschmitt Me 262, nicknamed (German for "Swallow") in fighter versions, or ("Storm Bird") in fighter-bomber versions, is a fighter aircraft and fighter-bomber that was designed and produced by the German aircraft manufacturer Messers ...

jet fighter late in

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. However, the first commercial airplane with this system (named AutoPower) was the DC-3 (since 1956). The first version was able to keep a constant

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...

but speed-only during approach. When the possibility of maintaining speed during an entire flight was introduced, it led to the creation of the modern autothrottle. The RA-5C Vigilante used an autothrottle actuated by the input from

accelerometers An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change of velocity) of the object relative to an observer who is in free fall (that is, relative to an inertia ...

installed in the tail which caused the throttle to be sensitive to movement of the stabilator. This allowed the pilot to adjust the throttle setting during landing approach by stick input alone.https://airwingmedia.com/downloads/a5-vigilante/ Shortly after AutoPower's success, two companies, Sperry (now part of Honeywell) and Collins started competing in the development of an autothrottle, with more and more liners and business jets being equipped with it. Today, it is often linked to a Flight Management System.

FADEC A full authority digital engine (or electronics) control (FADEC) is a system consisting of a digital computer, called an "electronic engine controller" (EEC) or " engine control unit" (ECU), and its related accessories that control all aspects of a ...

is an extension of the autothrottle concept and controls many other parameters besides fuel flow.

References

External links

* {{Flight instruments Aircraft controls Aircraft propulsion components

Working modes

Usage

History

See also

References

External links