An autothrottle - called automatic throttle, autothrust, A/T, or A/THR - lets pilots command a desired speed, rate of climb, or flight path while the system itself meters fuel flow to the engines. Once armed and the thrust levers are advanced past the detent, the device takes over, nudging power up or down so the aircraft holds the selected parameter more precisely than any human hand. Although an autothrottle can be thought of as a separate unit, it is designed to operate in unison with the autopilot; the two systems typically synchronize, with pitch coupling allowing thrust to track changes in aircraft attitude automatically.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is an autothrottle on a plane?
An autothrottle enables a pilot to control the thrust setting of the aircraft engines by selection of a specific flight profile rather than by controlling fuel flow via manual manipulation of the thrust levers.
Autothrottle is an electronic or electro-mechanical device, alternatively known as automatic throttle, autothrust, A/T, or A/THR. It is a separate system from the autopilot, yet it can be used with it; together, the autothrottle and the Autopilot Flight Director System (AFDS) form the Automatic Flight System that can fulfill the whole flight plan. The electromechanical system moves thrust levers automatically as the need for power changes, calculating engine power more accurately than any human.
What does auto throttle do on an aircraft?
Autothrottle (Automatic Throttle) enables a pilot to control the thrust/power setting of the aircraft engines rather than by controlling fuel flow via manual manipulation of the thrust/power levers. It calculates engine power more accurately than any human, adjusts power as required by flight parameters, and controls fuel flow. An Automatic Throttle reduces the pilots' workload, helps conserve fuel, reduces wear and tear on engines by using only required power, and helps extend engine fettle.
Autothrottle works with AFDS (Auto Flight Director Systems) and can operate in thrust mode. It can provide over-speed protection and under-speed protection. During take-off, pressing the TO/GA switch when autothrottle is employed activates the thrust lever servo-actuators and advances the thrust levers at a preset rate to the position for take-off or go-around. Pressing the TO/GA button results in auto-thrust advancing the engines to maximum available thrust. Autothrottles will power the engines up to the maximum limit for that phase of flight.
On Boeing aircraft, autothrottles physically move based on engine power, while on Airbus aircraft, the thrust levers remain in a stationary detent and do not physically move as engine power changes. On aircraft where TO/GA mode is selected manually, like current Airbus types, the thrust levers must be moved to the TO/GA detent. FADEC manages all aspects of engine operation.
Why do pilots throttle up an airplane?
Pilots usually throttle up for takeoff. Advancing the thrust levers to a mid-range setting first stabilizes engines and keeps engines spooled, and slowly pushing throttle to TO/GA while pilots allow engines' N1 and N2 spools to stabilize eliminates asymmetric thrust. After this stabilization, pilots push throttle to full and begin to accelerate for takeoff, producing the thrust that moves the aircraft forward; engines then spool up gradually and do not jump to maximum power immediately.
One pilot confirms that the commanded thrust is stable, while the other pilot focuses on speed calls after confirming thrust, reducing thrust when performance calculation allows it, thereby protecting engines and lowering fuel costs while maintaining certified safety margins.
