HOW IT WORKS

A WHOLE NEW WAY OF LOOK­ING AT FLIGHT DATA

Flying - - CONTENTS - By Rob Mark

An in-depth look at pri­mary flight dis­plays

It doesn’t much mat­ter whether Boe­ing in­tended to set off a rev­o­lu­tion in cock­pit in­stru­men­ta­tion when it de­liv­ered the first 767 in the early 1980s. That, of course, was the re­sult when the new jet­liner un­leashed the first com­put­er­ized cock­pit dis­plays des­tined to for­ever change the way pi­lots con­trol and nav­i­gate air­craft. The new in­stru­men­ta­tion quickly came to be called the glass cock­pit.

Round flight in­stru­ment gauges usu­ally or­ga­nized in two rows of three in­stru­ments each were re­placed with com­puter-gen­er­ated graph­i­cal rep­re­sen­ta­tions of an at­ti­tude and head­ing in­di­ca­tor, as well as those for air­speed, ver­ti­cal speed, turn co­or­di­na­tor and al­time­ter. Not only were the new in­stru­ments more ef­fi­ciently or­ga­nized to present in­for­ma­tion on the CRT screen used to dis­play them, but they also added color and move­ment where none had ex­isted be­fore. The cen­tral CRT came to be known as a pri­mary flight dis­play. Ad­di­tional CRTs were used to show im­por­tant nav­i­ga­tion and weather in­for­ma­tion on what be­came known as mul­ti­func­tion dis­plays.

The evo­lu­tion of tech­ni­cally ad­vanced air­craft in the early 21st cen­tury brought PFDs and their vast wealth of in­for­ma­tion to gen­eral avi­a­tion air­craft such as the Cir­rus SR20 and SR22. Most other ma­jor air­craft builders quickly fol­lowed suit with their own glass cock­pits. To­day, it is pretty much im­pos­si­ble to buy a new high-per­for­mance air­plane from any of the big orig­i­nal equip­ment man­u­fac­tur­ers that is not equipped with glass in­stru­men­ta­tion.

Glass flight-in­stru­ment dis­plays are usu­ally fed by many of the same data sources as the old round gauges, such as pitot tubes and static ports. The dif­fer­ence now is that a PFD uses a com­put­er­ized sig­nal gen­er­a­tor to trans­late that data into vis­i­ble images, much the same way col­or­ful, an­i­mated games are cre­ated for per­sonal com­put­ers. One huge ad­van­tage of a PFD and its associated equip­ment is that these sys­tems are cre­ated with few mov­ing parts, which makes them highly re­li­able.

The PFD rev­o­lu­tion­ized pi­lot train­ing as well as air­craft con­trol. Years ago, pi­lots earning an in­stru­ment rat­ing were taught a ba­sic in­stru­ment scan, a pro­ce­dure to en­sure the PIC was aware of even the slight­est head­ing, al­ti­tude, or air­speed trends or changes. These ef­forts of­ten kept a pi­lot’s head mov­ing most of the time, of­ten caus­ing fa­tigue.

The PFD’s graph­i­cal world dis­plays all the nec­es­sary flight in­for­ma­tion in a for­mat that much re­duced the need for that con­stant left-right, up-down scan. The PFD not only made fix­at­ing on one in­stru­ment less com­mon, but the en­tire sys­tem helped re­duce a pi­lot’s over­all work­load, once their eyes be­came used to see­ing the in­for­ma­tion pre­sented in a new for­mat, of course. In the early days of the Boe­ing 767, there were some pi­lots un­able to make the leap from the old round gauges to a glass cock­pit.

When a pi­lot views the at­ti­tude in­di­ca­tor on a PFD, for ex­am­ple, the new col­orized sym­bol­ogy makes it easier for a pi­lot to de­ter­mine the air­craft’s air­speed, head­ing, al­ti­tude and ver­ti­cal speed at al­most the same moment. No need to in­ter­po­late an air­speed as some­where be­tween 120 and 140; the PFD shows it as pre­cisely 133 knots, or an al­ti­tude at 5,750 feet.

In ad­di­tion to the PFD’s color graph­ics and pre­cise dig­i­tal dis­plays, the new in­stru­ment dis­plays be­gan show­ing in­for­ma­tion ver­ti­cally, a change that made trends easier to track. Nav­i­ga­tion in­for­ma­tion was also in­cor­po­rated into the PFD, with the lo­cal­izer nee­dle shown just be­neath the at­ti­tude dis­play in­di­ca­tor. The glides­lope ran ver­ti­cally to the right of the ADI. Even the turn co­or­di­na­tor was neatly added at the top of the ADI, mak­ing it easier to be in­cluded in the pi­lot’s in­stru­ment scan for more-pre­cise air­craft con­trol.

As ma­jor avion­ics man­u­fac­tur­ers such as Garmin, Honey­well, Rock­well Collins and Avi­dyne con­tin­ued im­prov­ing their prod­ucts, pi­lots no­ticed the ad­di­tion of use­ful fig­ures, such as best an­gle or best-rate-of-climb speeds, that tra­di­tion­ally would have been com­mit­ted to mem­ory. Most new at­ti­tude in­di­ca­tors now of­fer pi­lots graph­i­cal guid­ance to as­sist with re­cov­ery from an up­set con­di­tion, air­borne traf­fic and even weather in­for­ma­tion.

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