The Real Glass Cockpit Question


There has been a great deal of discussion about the difficulty, or lack of it, of transitioning from conventional flight instruments to flat-panel primary flight displays (PFD). Many also worry that new instrument pilots who learn on a PFD will find it very difficult to fly safely with a conventional round dial set of gyros and air data instruments.

To my knowledge there has been no conclusive study that shows competent instrument pilots have problems going between flat glass and conventional instruments. I know that I have not experienced a problem flying whatever is in front of me. In fact, my very first flight with a PFD was in the Gulfstream IV, the first civilian airplane to have such a display, and the weather was 400-feet overcast. So in a few seconds after rotation I was on solid instruments with a totally new type of display, and it felt perfectly natural.

If I had to choose between conven-tional instruments and a PFD, I would always take the glass. I think it may be a little easier to scan the information without my eyes moving across the hardware that separates conventional instruments and the data they present. And certainly the airspeed and altitude trend vectors that are a part of a PFD make precise flying easier.

But a PFD is the baby step in making IFR flying less complicated and more precise. It doesn't change the fundamental pilot task, but does make it a little easier. But the real breakthrough is having the glass display and the computer behind it do the thinking for you, not just show you the same data in a different way. And it can do that now.

If you reduce instrument flying to its basics you find that only two questions must be constantly answered-where am I now, and where am I going. When a human flies IFR using conventional instruments, or a PFD, his brain must function as a computer that takes the available information and answers those two fundamental questions.

For example, it's essential to know the attitude of the airplane because that determines where the airplane is going. But airspeed, heading and vertical speed also must be considered to know where the airplane will be within the next few seconds. Altitude and course information tell you where you are now. It is a very complex task to mentally process all of this data in real time and do it almost subconsciously so that you have working memory available for that new heading, altitude, frequency or clearance the controller just read to you.

Whether the dynamic raw information is presented to a pilot on a PFD or mechanical dials is a small difference when you consider the enormity of the workload of taking that information and constantly computing and visualizing your airplane's path through the air and over the ground. The task is so complex, in fact, that computers really couldn't do it well until a very important piece of information the human pilot doesn't have is added, and that is acceleration vectors.

Acceleration is nothing more than a change in the flight path and speed of the airplane. The human mentally computes a crude acceleration vector by noting changes in the basic instruments. But there is quite a lag in the time it takes for the human pilot to note a change in altitude, for example, comprehend that change, and then consider if the change is desired or must be corrected. Flight director and autopilot computers with their unwavering electronic concentration do a better job of computing accelerations and correcting for them than we humans can, but it is still a second order solution based on change in data such as attitude, heading, airspeed or altitude, and there are lags in measuring those data.

Precise flight guidance really comes from inertial devices that directly measure acceleration vectors and thus compute the airplane's path through the air and over the earth. Inertial sensors were once exclusive to the most expensive civilian jets or the military. The first inertial navigation systems were among the most highly classified of military equipment because only they could guide intercontinental missiles to their targets. When the inertial equipment was made available to civilians it was so big and heavy, and expensive, that it could fit only in airliners, or the largest business jets.

The ring laser gyro shrank the size and weight of the inertial sensors, but not the price, so the equipment remained unavailable to even midsize business jets. But now high-speed computer chips and miniature electromechanical sensors have made it possible for even piston singles to carry inertial sensors. That's what the nonmoving attitude heading reference systems (AHRS) in the Garmin G1000, Avidyne Entegra and other glass cockpit systems are-inertial sensors.

With an inertial sensor onboard it is possible to compute a precise flight path without the pilot having to integrate and process the raw data we have been using. The inertial sensor measures very tiny changes in the acceleration vector and projects them many seconds ahead to show where the airplane will be. With this information the instrument pilot's job becomes something like point and shoot. Just keep the flight path pointed at where you want to go, and you will get there without processing much additional information.

• This is an example of Rockwell Collins' ideas for highway in the sky with synthetic vision.

Presenting flight path guidance to pilots is not that new. The military has displayed flight path on heads-up displays (HUD) for many years. Flight Dynamics, now a part of Rockwell Collins, used the precision of inertial flight path guidance to certify many years ago a HUD to Category II low approach minimums with no need for extra ILS precision that had been required. Falcon has made flight path the primary flight display in its EASy glass cockpit system, and Chelton shows flight path on its primary display designed for propeller airplanes.

Once flight path information is available then all sorts of new primary display techniques and symbology start to make sense. A highway in the sky is easy to fly with flight path guidance because if you put the flight path symbol on the display object you want to fly to, you will get there, no matter what the attitude of the airplane. The topographical displays of synthetic vision make total sense with flight path guidance because you see instantly if your path will miss terrain or take you to the synthetic display of the runway.

Synthetic vision is coming on fast and will soon be available in most any airplane with a glass cockpit. Synthetic vision systems (SVS) search a stored map of the terrain and topographical features around the airplane and present the information as an electronic picture of the world below and around you. SVS is a great aid for instant orientation and to avoid a gross error that could lead you into terrain.

Airspeed guidance is a natural component of flight path computation because the acceleration measurements instantly report if you are gaining or losing speed compared to the target value. An autothrottle to maintain target speed is best, but the human can do a decent job simply by following the speed cue.

I often tell student pilots-or new sailors, for that matter-that airplanes and boats seldom go exactly where they are pointed. Wind makes airplanes drift left and right, and a very complex combination of attitude and power make an airplane go up or down. On either round dial instruments or a flat glass PFD, all we see is where the airplane is pointed and we must compute where it is going. With flight path guidance, the electronic computer handles that chore, leaving us to ponder if that is, in fact, where we really want to go.

So I am glad to have PFDs in all sizes of airplanes, and they are better, but now that we have that glass and the sensors and computing power to go with it, I hope the heavy lifting will soon be left to the electronics. For we old farts with decades of staring at raw data instruments, it is almost second nature to compute our flight path. But it's unnecessary and should go the way of the four-course range and ADF. Just because it is possible to perform a complicated mental task doesn't mean it is a good use of a pilot's time when there is so much other information to process.

Exactly what form a primary flight path display should take has not been determined, and there are many versions being developed, tested in the laboratory, or actually flying. I'm not sure any have been fully optimized, but I want to see the avionics and airframe makers commit to flight path guidance and provide it in all IFR airplanes that have flat glass displays. The technology is here now, the cost is not significantly different, but the precision guidance and workload reduction benefits will be enormous.

Low Lead Questions Allen Bretz, who is director of general aviation marketing for ConocoPhillips, made some comments about the continued availability of 100LL avgas earlier this year that are not totally comforting, but not alarmist, either. Phillips 66, along with Avfuel, are the leading suppliers of avgas and thus have a good handle on the situation.

In speaking to a warbird conference Bretz said that avgas sales are at best flat, while jet fuel sales are soaring. He reported that only 320-million gallons of avgas were sold in the United States in 2006, which equals about three-tenths of one percent of all motor fuel volume. Pretty small potatoes.

Leading the worries about avgas availability are any actions by the EPA that would ban leaded fuels, but Bretz sees no move by the EPA to do this at this time. Also, there is only one source of tetraethyl lead, a British company, but it has assured Phillips and the rest of the industry that it foresees no shortage of the additive to meet current demand, or any likely increase. Bretz reported that there are 11 refineries in the United States currently producing avgas, and ConocoPhillips owns three of them. Some of the other refineries have fallen behind on avgas production due to demands for the many blends of automobile gas, but the ConocoPhillips refineries have maintained a steady production.

There is also an issue in the piston airplane fleet mix. Phillips 66 finds that 80 percent of all piston-powered airplanes could use a lower octane fuel, such as mogas, but the 20 percent of airplanes that need 100LL burn 70 percent of the total avgas volume. The high-powered airplanes fly more, and burn more fuel, so the comparative few are the heart of the avgas market. With 70 percent of the avgas going into airplanes that can't use any less octane, there is no realistic alternative to 100LL avgas at this time for the overall piston fleet. Ethanol has been examined as an avgas additive but its lower energy content would reduce aircraft performance and range by as much as 30 percent, and would almost certainly damage existing engines and fuel system components.

Bottom line, Bretz reports that the outlook for a continued supply of 100LL from ConocoPhillips "is very positive." He didn't guess when fuel prices may come down, but at least we can count on a continued supply.

Turboprop Competition Everybody loves the Pratt & Whitney PT6 family of turboprop engines. It is the world's favorite and deserves all of the respect for reliability and excellent support that it universally receives. But the PT6 needs some competition. The engine is so dominant that it's hard for me to believe the guys in Canada are sharpening the pencils when an airplane maker comes shopping for a new turboprop engine.

But maybe that will change. General Electric has made an agreement to buy the Czech turboprop maker Walter Engines. GE is, of course, a world leader in turbine engines and has extensive capabilities in engineering, manufacturing and support.

Walter's M601 engine has the same basic layout as the PT6 with the air intake at the rear and the air flowing forward through the gas generator section, then over the power turbine to drive the propeller gearbox. The Walter has been approved as a conversion in some PT6 applications and can be installed without huge changes to the airframe.

The Walter has an okay reputation, but does not match the PT6 in measures of operating life and fuel efficiency. But the Walter is substantially less expensive. So, with GE's expert input, maybe the Walter can close the performance gaps with the PT6 while still maintaining a price advantage. If so, that would give airframe makers a new option to bring personal turboprops to market at a more attractive price.

We have seen what competition among engine makers can do in the small turbofan area where Pratt & Whitney and Williams are fighting it out to get their engines on the new crop of small jets. One of the reasons that the Citation Mustang with its twin turbofans, for example, can be priced about the same as the single-engine turboprop TBM 850 is engine cost. The small Pratt jet engines are delivering more thrust for the dollar than the PT6 the TBM uses. I hope that GE and Walter can bring the same style of competition and value to the turboprop engine business.


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