A SYSTEM TO ADJUST ENGINE POWER, AND HENCE SPEED, REPRESENTS THE NEXT LOGICAL FOLLOW-UP PRODUCT TO THE AIRCRAFT’S AUTOPILOT.
Precision flying demands a pilot honing the ability to finely tune their inputs to the ailerons, elevators and rudder, tasks autopilots have proven they can handle better than humans. Of course, precision flying wouldn’t exist if not also for a gentle hand on the throttles. Auto-throttles, the next logical step in cockpit automation, make short work of this chore. Think of auto-throttles like a cruise control for airplanes, automation that frees the pilot to focus on more pressing tasks, especially if he or she is the only person aboard. Auto-throttles, long standard on jets, have now made their way to a variety of turboprops.
This automated speed control is typically engaged as the flying pilot
completes the lineup checks on the runway prior to brake release. As the throttles are advanced for takeoff, most systems are engaged when the pilot presses the “A/T Engage” button on the side of the throttles. Auto-throttles aboard Dassualt’s Falcon 7X, however, won’t engage until the aircraft is at least 400 feet in the air to ensure full pilot control over the engines during an emergency.
There are a few other auto-throttle idiosyncrasies. On a Boeing, or Embraer, the throttles actually move on the pedestal in most cases as visual confirmation of the requested speed. In an Airbus, however, the throttles remain stationary. The only way to confirm a requested Airbus speed increase is to keep an eye out for a change on the engine gauges or the airspeed indicator. The pros and cons of moving versus stationary throttles have been debated over the past 30 years, with each side believing their system to be the best.
Despite fully automated throttle action, the wise aviator still keeps a hand on the controls in case of a rejected takeoff when seconds count. On takeoff, the auto-throttles assume the pilot will call for maximum power and adjust for the best thrust settings after considering the outside air temperature and density altitude. Most systems will also engage automatically when they sense an impending stall.
The speed the aircraft maintains once free of the earth is dependent upon the number the pilot requests in the speed control on the guidance panel and the engine power required to achieve that number. In the case of total aircraft automation, when a stored flight plan generally includes speeds for all takeoff, cruise and approach speed configurations, the autopilot, and hence the auto-throttles, will follow the preprogrammed numbers in the flight management system.
As the aircraft levels off at a predetermined altitude, a cockpit observer shouldn’t be surprised to watch the aircraft’s nose pitch over to maintain altitude as the auto-throttles’ invisible hand pulls the levers back for the correct power setting.
Auto-throttle technology is relatively simple with the speed control on the flight guidance panel normally connected through the primary flight display to confirm the actual speed being requested. The angle of the throttles in the quadrant is preprogrammed to deliver a particular power setting. An electrical link from the PFD is then routed through the air data computer and the autopilot control before activating a small electric motor attached to the base of each throttle lever that sets the throttle lever angle to the required power.
A Auto-throttles are normally engaged just before takeoff when the pilot presses an “A/T” button. B In most systems, the throttles themselves move in response to the pilot’s speed inputs. C The link between the requested airspeed and the movement of the throttles runs through the primary flight display. D Each throttle lever itself is equipped with its own electric motor to handle the actual movement requests.