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Oz: A Revolution in Cockpit Display

By Adrian Gerold | October 1, 2003
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Two Florida scientists have developed a unique approach to solving the problem of flight deck information overload, sometimes called "the tyranny of numbers." Their solution is a pilot display concept called OZ. It could completely revolutionize aircraft instrument panels.

More than most other human endeavors, flying an airplane requires that pilots know by heart a large vocabulary of numbers for such calculations as airspeed, bank angle, power settings, and engine temperature limits, among many others. But unlike the vocabulary of words, where meanings almost always remain the same, the meanings of aircraft numbers can change dramatically, yet quite normally, during every flight.

Pilots must therefore know almost instinctively whether any of those changes are normal, or potentially hazardous,

because there's often no time to check the flight manual. For example, a stall occurs when an aircraft’s wings lose lift below a certain speed, and the aircraft then drops. But that speed can vary greatly, depending on such things as wing flap settings, power, weight, bank angle and other factors.

Consequently, pilots are taught from the very beginning to develop an "instrument scan" technique, where they periodically look over their flight and engine instruments, plus all other indicators relevant to their present flight phase. They then mentally integrate all this information to determine the aircraft’s current state and subsequently compare this knowledge with what would normally be expected at the time. Adding complication is the fact that today’s instruments present their data in a mixture of different units: knots, feet, pounds, degrees, percentages, etc., and at a mixture of different scales, presented in different areas of the cockpit. And tests have shown that even experienced pilots spend up to half a second, and sometimes longer, looking at each data display in order to properly absorb its meaning, before moving on to the next display.

Must Be a Better Way

David Still and Leonard Temme decided there had to be a better solution–one that presents all this information continuously on a single display, while remaining instantly understandable to the pilot. Still, a retired U.S. Navy commander with two doctorates in vision science, is now a researcher with the University of West Florida at Pensacola. He also is a private pilot building a Rutan Long Eze, a rather exotic looking, private, two-seat aircraft. Temme is a neuropsychologist who works at the nearby Naval Aerospace Medical Research Laboratory.

The result of their research and development effort is OZ, an instrument display concept that is totally different from anything ever made available. What's more, the OZ concept can be applied to all aircraft: fixed- and rotary-wing, large or small, civil or military. U.S. Navy and NASA researchers agreed with their thinking, and have provided $1.2 million in development funding.

Why is the concept called OZ? It’s because an early prototype required a technician to work behind a curtain, reminiscent of the 1939 classic movie, "The Wizard of Oz."

The key to OZ lies in its single display’s use of carefully tailored graphic symbols, rather than numbers. Also key is the use of two separate characteristics of the human eye–the focal channel and the ambient channel–to view all the symbols simultaneously.

"Think of a running [football] quarterback passing the ball to a receiver, or a driver reading a road sign as he steers the car around a curve," explains Still. "In both cases, the focal channel concentrates on a single specific object, i.e., the receiver or the sign, while the ambient channel monitors the surrounding scene in a much broader way, to avoid being tackled or drifting off the road."

Using Both Channels

And this is where the critical difference comes in between performing a conventional instrument scan and using OZ. With the conventional scan, the focal channel concentrates on each individual instrument indication in turn, while the ambient channel is largely unused. With OZ, both channels are operating full time.

Does the dual-channel concept work? Unquestionably, yes, and astonishingly well. During a recent visit to the University of West Florida's Institute for Human and Machine Cognition, I flew an OZ simulator, and was deeply impressed.

True, OZ looks weird. The aircraft’s heading is obvious enough, with its band across the top of the screen and the heading reciprocal displayed on a second band across the bottom. But the rest of the symbology initially is baffling.

For example, what do those four cranked wings do? Actually they each represent the aircraft’s aerodynamic lift/drag curve, since OZ is computer-tailored to each specific type of aircraft. The vertical struts are symbolic airspeed bars, which move along the wings from stall speed at their inner ends to the aircraft's maximum allowable speed at their outer tips. (The wings' crank point indicates the speed for maximum lift.)

If the pilot lowers the landing flaps, which in turn lowers the aircraft’s stall speed, the inner ends of the gull wings automatically extend further inward. Conversely, if the pilot banks the aircraft, which causes its stall speed to increase as the bank angle increases, the inner ends of the gull wings move outwards to the now higher stall speed limit.

The broken horizontal line between the wings represents the airplane, like the airplane wings in the traditional artificial horizon. Centering the vertical struts in the circles along that line gives your desired airspeed, which you set for that phase of flight. With the vertical struts centered, level flight at that speed is obtained by smoothly adjusting the engine power to cause the green sections of the struts to just touch the upper and lower wings. And all of the above is achieved very accurately and very simply, without the need to monitor any numbers on the display screen.

The gull wings, too, assist in maneuvering. Banking the aircraft to align an outer wing section with the horizon puts the aircraft into a correctly banked attitude to achieve what pilots call a standard rate turn. Executed at precisely three degrees per second, this bank attitude is a common requirement in most instrument flying procedures.

Interestingly, the actual bank angle for such a turn varies with an aircraft's speed. But the OZ computer is tailored to the flight characteristics of each aircraft type and also receives digital airspeed data. So the simple act of aligning the outer wing with the horizon produces the correct bank angle, whatever the aircraft.

Similarly, placing the bottom or the top of the center circle on the display's horizon causes the aircraft to climb or descend at a precisely preset rate, appropriate to the aircraft type. And again, without the need to check any numbers.

Following the Stars

The OZ horizon is particularly ingenious. The display covers 90 degrees, either side of the heading, and extends +/- 30 degrees vertically, and more for higher-performance airplanes. But instead of the usual flat backgrounds of blue sky and brown earth on the traditional artificial horizon–and also even on today's electronic attitude indicators–OZ uses a "star field." Here, streams of blue stars, spaced 30 degrees apart, continuously flow out towards you from the screen's center. (Think of Star Trek’s spaceship Enterprise going into warp drive, but a lot slower.) Whatever your altitude, the stars create a horizon bar across the screen, while presetting a target cruise altitude produces a bright red bar at that height. (And yes, in deference to tradition, stars passing below you do turn brown.)

The star field provides an additional, powerful benefit. Over the years, there have been several fatal accidents, where less experienced pilots have become disoriented in clouds or on dark nights or after a turbulence upset event and have been unable to recover safely. The OZ star-field display makes a prompt recovery maneuver in such situations totally intuitive–and safe.

Numbers Still There

For the added comfort of pilots newly introduced to OZ, the full numerical values, like airspeed, altitude, etc., can be displayed beside their respective symbols. Numbers can appear next to symbolic limit warnings for power settings, engine instrument readings, trim, undercarriage and other things. With familiarity, however, the symbols are all you need, and one can gradually declutter the screen by deleting the numbers, with the exception of the heading band, which is permanently displayed.

The OZ display also offers many other selectable features in its forward field of view, including navaids, airports and even other aircraft, in a traffic alert collision avoidance system (TCAS) or automatic dependent surveillance-broadcast (ADS-B) environment. In this case, nearby traffic can be presented at the appropriate ranges, bearings and locations above and below the horizon.

And going one step further, the OZ system even has an intriguing "rear view mirror" feature, which you have to fly to appreciate. Employing a map database and GPS receiver for aircraft position, this feature is extraordinarily helpful during instrument procedures. It provides a 180-degree perspective. So, as you overfly an airport, the aircraft symbol on the screen moves to the bottom of the map imagery. And then, after passing the airport, the symbol moves up the screen again in a way that–believe it or not–clearly indicates your distance from the airport. This feature is particularly beneficial when turning and lining up with the center line to make the final approach.

As mentioned, OZ is now in development, but Still and Temme are looking for a suitable small aircraft to commence flight tests. Market entry is, of course, some years away, due both to the exacting nature of certification regulations and the system’s very unique characteristics. Indeed, these characteristics may well demand some rewriting of the rules. Nevertheless, it seems certain that we will hear and see much more of OZ and its revolutionary concepts in the future.

Flying the OZ Simulator

As a reasonably experienced pilot, with a fair amount of instrument flying time in several different aircraft types, I was somewhat skeptical about OZ. But then I flew the simulator, which was programmed to replicate the performance and handling characteristics of the Cessna 172. In fact, an adjacent display showed the identical flight situation on a simulated Cessna 172 cockpit, and one could alternate between the two.

Two things struck me immediately. First, the OZ display was easy, almost instinctive, to understand and to fly without referring to numbers. Second, it was far easier to maintain accurate headings, speeds and altitudes with OZ than with the occasionally skittish Cessna, a fact borne out strongly in earlier tests with non-pilot subjects who alternated between the two.

Not too long after getting the feel of OZ, I flew a simulated ILS approach. It required nowhere near the concentration that the 172’s conventional panel would have called for. And, while the Cessna’s performance envelope inhibited severe attitude maneuvers, safe recovery to level flight from those that could be performed was obvious and easily accomplished.

My conclusion: OZ could be the most significant development in instrument flight since Elmer Sperry invented the artificial horizon in the 1920s.

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