What is Auto Throttle?
An auto throttle (also known as autothrust, A/T, or A/THR) is a sophisticated system that automatically controls engine power settings. Instead of manually adjusting thrust levers manually, pilots simply specify their desired flight characteristic—airspeed, climb rate, or another parameter. The system then acts as an automated assistant, continuously monitoring flight data and adjusting engine thrust to maintain that target, improving both cockpit efficiency and flight efficiency.
Auto throttle systems are now standard equipment across commercial airliners, business jets, and many advanced aircraft. These systems have become essential equipment in modern aviation. While terminology shifts between manufacturers—Airbus favors ‘autothrust,’ Boeing champions ‘autothrottle’—the fundamental purpose stays the same: intelligent automation of engine power to achieve optimal flight performance.
How Autothrottle Works
The autothrottle system works by connecting between the aircraft’s flight management computers and its power plants. Once engaged, it controls engine power, automatically fine-tuning engine output through precise fuel flow control based on real-time flight data. The system monitors parameters like airspeed, altitude, vertical speed, and aircraft weight, and calculates the required thrust to maintain the desired flight profile.
In practice, the autothrottle moves the thrust levers on the throttle quadrant. Need more power? The system smoothly advances the levers forward, increasing fuel flow to the engines. Less power required? It gracefully pulls them back, reducing fuel delivery. This happens automatically without demanding pilot intervention, though pilots retain absolute authority to override the system whenever manual control becomes necessary.
Autothrottle systems effectively manage engine power throughout all flight phases. During takeoff, they can automatically establish and sustain takeoff thrust. Throughout climb, cruise, and descent phases, they dynamically adjust power to meet speed targets, altitude restrictions, and performance demands.
Modes of Autothrottle
Most autothrottle systems operate in two fundamental modes:
These modes work together with other automated systems. When married to the autopilot and flight management system, the autothrottle becomes part of an integrated system that can manage the entire flight profile from takeoff to touchdown. Pilots can seamlessly select between these modes based on operational needs, weather challenges, or specific flight procedures—always retaining the power to assume manual control when circumstances demand direct intervention.
Benefits of Using Autothrottle
Autothrottle systems provide several key benefits:
Safety Features of Autothrottle
Autothrottle systems include sophisticated safety mechanisms to maintain the aircraft within its protective flight envelope:
These protective features work with the aircraft’s broader envelope protection network, providing multiple layers of protection. Working with other automated systems and minimizing human error in throttle management, autothrottles significantly improve aviation safety—particularly during high-stress scenarios where precision becomes paramount.
Historical Development of Autothrottle Systems
The journey of autothrottle technology traces back to rudimentary systems during World War II, including early implementations on the Messerschmitt Me 262. The aviation world witnessed its first commercial breakthrough with Automower® on the DC-3 in 1956—a pioneering step that established the foundation for today’s sophisticated technology.
Military applications throughout the Cold War era drove significant improvements. One notable development was with the accelerometer-actuated autothrottle on the RA-5C Vigilante, allowing much more responsive power adjustments. During this transformative period, industry giants like Sperry and Collins became leaders, developing increasingly sophisticated systems.
The contemporary era features deep integration with Flight Management Systems (FMS) and Full Authority Digital Engine Control (FADE). This integration allows autothrottles to manage complete flight profiles—from initial takeoff thrust to final landing flare—evolving far beyond simple speed maintenance. This development has made autothrottle from optional equipment to an essential, fundamental component in modern flight decks.
Common Issues and Misunderstandings
While autothrottles offer many advantages, autothrottles present several challenges that demand pilot vigilance:
