Autothrottles – An extra pair of hands in the cockpit

Flying an airplane smoothly demands dozens of subtle, often repetitive movements, like adjusting engine power each time the aircraft’s pitch attitude changes. Any repetitive process is, of course, perfect for some form of automation. Leonard Greene understood that nearly 70 years ago when he created the first commercial autothrottle system. Greene founded the New York-based Safe Flight Instrument Company, also known for its angle-of-attack and stall warning systems.

A few definitions first. Boeing calls its installed system an autothrottle, while a similar system on an Airbus is known as autothrust. Autothrottles typically synchronize with the autopilot and operate in either speed or thrust mode, creating many practical hands-free benefits, like flight envelope over- and under-speed protection. Typically connected to the aircraft through the flight management system (FMS) computer and an outside air temperature sensor, the autothrottle calculates engine power more accurately than any human. During an instrument approach or on a standard terminal arrival route (STAR), autothrottles relieve the pilot of the throttle-jockeying work during required speed changes. If the autothrottles are switched off or become inoperative, the flying pilot can easily revert to flying the aircraft by adjusting the throttles manually.

During an engine failure aboard a multiengine airplane, the autothrottle automatically sets the best power on the good engine. Many modern aircraft also offer an additional power boost in case of an engine failure during takeoff known as reserve thrust. This system boosts the good engine at takeoff or go-around when it senses a difference between both engine low-speed fan (N1) values of more than 15 percent.

Today, most transport category aircraft from Boeing, Airbus, and Embraer, and most major business jets produced by Cessna, Bombardier, Dassault, Gulfstream, and Honda are equipped with autothrottles. Some single-engine jets like the Cirrus Vision Jet and turboprops like the Pilatus PC–12 and the Daher TBM 900 series are also autothrottle equipped. General aviation aircraft that use Garmin’s Autoland system, in fact, require Garmin’s autothrottles installed.

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(Reprinted courtesy of AOPA Pilot)