Most pilots believe that it's easier to fly IFR with a big flat-glass primary flight display (PFD) instead of the six-pack of mechanical instruments. Until recently I wasn't convinced. I don't know of any controlled studies that have compared the pilot workload, or the precision of basic attitude, altitude, heading and airspeed control, when flying the electronic PFD or mechanical steam gauges. There has been considerable human factors research into various symbols and graphical presentation of primary flight instruments, but I don't know of any experiments that have taken significantly sized groups of non-instrument rated pilots and trained a control group on one type of display and compared it to the performance of a similar group using the other style of instruments.
Opinions by experienced IFR pilots on the subject are almost meaningless. I am convinced that a pilot with a well-developed instrument scan and good situational awareness will do a perfectly fine job of flying with either style of display.
But when the first PFDs were being developed industry experts were not convinced that transitioning to electronic displays would be seamless for experienced pilots. And at that time only experienced pilots were of concern because electronic flight instruments of all types were restricted to very expensive turbine airplanes because of high costs.
The first widely used electronic displays -- EFIS they were then called -- were in the Boeing 767/757 and they were essentially TV pictures of a conventional flight director and horizontal situation indicator (HSI). There was some added information including a track display on the HSI but there was little new for airline pilots to learn because the look was so much like the mechanical instruments the EFIS replaced. The technical breakthrough was to make a CRT display bright and sharp enough to be clearly visible in the cockpit under all lighting conditions.
EFIS displays quickly found their way into business jets, with the Falcon 100, the follow-on model of the small and very fast Falcon 10, the first production jet to be fully equipped. The common wisdom among the industry experts was that younger, more technically savvy pilots would adapt to EFIS quickly, but the older gray heads would resist. Most opined that the older pilots would insist on retaining traditional mechanical instruments on one side of the cockpit for comfort of the familiar.
The experts were all wrong. EFIS was accepted instantly by pilots of all ages. The only airplanes that had the mechanical displays on one side did so as a cost-saving measure, not for worry about the reliability and usefulness of the electronic displays.
The first actual PFD with all flight instruments presented on a single electronic display was developed by Honeywell and Gulfstream for the G-IV in the 1980s. The big difference between the PFD and what was by then common EFIS cockpits was the vertical tape displays of air data. There just wasn't room on the screen for large round displays of airspeed, altitude and vertical speed so they were presented as thermometer-style vertical tapes that appeared to scroll as the value changed.
All human factors research that I know of shows that a round dial delivers the most information to the human brain in the shortest amount of time. The briefest glance at a round dial display, such as a watch or clock, allows the human brain to gather the information presented with pretty good precision. The Movado Museum series of watches is a perfect demonstration of this. With only a single index mark at the 12 o'clock position it's easy to tell time on that style of watch within a minute or two with just a glance.
The display space available and other technical issues made the round dial display impossible. But how best to present altitude and airspeed on a vertical display? The altimeter was easy because a higher altitude is always above you, so the big numbers would be at the top of the display. But with airspeed the higher values are below you. An airplane accelerates when you lower the nose. So it made sense to the Gulfstream experimental test pilots to put the big airspeed numbers at the bottom of the tape.
My first takeoff in the G-IV, and first flight using any PFD, was into a 400-foot-high overcast and the presentation seemed perfectly natural from rotation. Part of the reason is that in jets it's standard procedure to set airspeed and altitude targets with "bugs" on the instrument. So instead of remembering a specific number, you fly to the bug you or your copilot set as the target. The other reason adaptation was easy is that the flight director format was the same, so I pitched the nose into the command bars to hold the target airspeed, altitude or heading just as I always had with mechanical instruments.
The reversed airspeed tape display in the G-IV was not adopted by any other airplane manufacturer that I know of, but the PFD was an instant success and quickly spread across the business jet fleet.
Collins Avionics was among the first to develop flat glass displays with its Pro Line 21 system, and that solved the technical limitations that had forced the use of vertical tape altitude and airspeed displays. The Beech Premier was the first announced program for the new Pro Line 21 system and it was to have had round dial airspeed and altitude displays on the PFD. I got to fly an experimental version of the PFD and it was excellent. The round dials were great and simply observing the position of the needle showed instantly if you were on target.
