Auto-throt­tles

A SYS­TEM TO AD­JUST EN­GINE POWER, AND HENCE SPEED, REP­RE­SENTS THE NEXT LOG­I­CAL FOL­LOW-UP PROD­UCT TO THE AIR­CRAFT’S AU­TOPI­LOT.

Flying - - Contents - By Rob Mark

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.

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