Unique Display: Putting OZ to the Test

By by Adrian Gerold | November 1, 2005
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In October 2003 Avionics Magazine reported on OZ, a revolutionary flight instrument display concept developed at the University of West Florida’s (UWF’s) Institute for Human and Machine Cognition at Pensacola. Since our visit to the Institute in 2003, further refinements to the system have been incorporated and some very demanding tests have been completed by highly experienced military jet instructor pilots. The results have been impressive.

OZ is the brainchild of David Still, a UWF researcher, and his associate, U.S. Navy neuropsychologist Leonard Temme. A retired U.S. Navy commander, Still possesses two doctorates in vision science. Their OZ system breaks away completely from conventional flight deck pointers and dials, presenting the pilot with a symbolic, yet instantaneously understood, picture of the total aircraft situation.

From their previous experience, Still and Temme knew that it takes a pilot about half a second to read and absorb the information from each flight and engine instrument during a typical instrument scan, an exercise performed frequently during each flight. But this could be too long in certain critical situations, creating the so-called "information overload." They therefore reasoned that a completely different display approach is required, to present the total flight data in a way that is both immediate and instinctive, and yet accurate.

The result was OZ, a very unusual, single-panel, "glass cockpit" presentation that, while appearing impossibly complex at first sight, turns out to be remarkably easy to adapt to–even by nonpilots and beginners who are often challenged by conventional instrument panels–and extraordinarily accurate to fly. The secret of OZ, Still explains, lies in its use of carefully tailored graphic symbols, rather than numbers, and in the use of two separate characteristics of the human eye, called the focal channel and the ambient channel, to view all the symbols simultaneously. "Think of a running quarterback passing the ball to a receiver or a driver reading a road sign as he steers the car around a curve," Still explains. In both cases, the focal channel concentrates on a single 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.

This is the critical difference between performing a conventional instrument scan and using OZ. In a conventional scan the focal channel concentrates on each individual instrument indication in turn, while the ambient channel is largely unused. With OZ both channels operate full time.

And why the system’s odd name? In an early iteration a technician performed certain functions while concealed behind a curtain, reminiscent of the Wizard in the epic 1939 movie. The technician is no longer required, but the name remains.

When Avionics Magazine visited Pensacola in 2003, the system had only recently been configured as a "flyable" simulator. But even then its advantages were quickly apparent when compared with an adjacent Cessna 172 cockpit simulator. At that time, Avionics Magazine simply put OZ through fairly conventional flight routines, including ILS approaches and some unusual attitude recoveries.

But since our visit, many pilots have flown the system, and Still and Temme have developed more challenging procedures to fully exercise its capabilities. Two of their tests were particularly interesting.

The first aimed to evaluate whether OZ helped pilots in stressful situations, where their "competency reserves" were stretched to the limit. A group of experienced military jet instructor pilots were given the relatively simple task of maintaining slow flight at specific speeds, headings and altitudes while being exposed, via special breathing masks, to atmospheric conditions at 18,000 feet. Normally, pilots breathe oxygen at sea level pressure above 10,000 feet since anoxia, or lack of oxygen, slowly impairs performance with increasing altitude, eventually leading to unconsciousness. Activities without supplementary oxygen at 18,000 feet become labored, and the ability to concentrate wanes rapidly.

With a medical specialist at hand, each pilot flew the same exercise during separate sessions in the Cessna and OZ simulators. The results showed that adherence to the required speed, heading and altitude were between 200 and 400 percent better with the intuitive display than with the Cessna’s conventional dials and pointers. In fact, it turned out that the pilots performed just as well flying OZ without supplementary oxygen, in simulated 18,000 feet atmospheric conditions, as they did flying the Cessna at sea level.

High-Speed ILS

The second test, designed and supervised by longtime jet instructor pilot, Stephen Harmon, exercised a separate group of experienced instructors in precision approach scenarios to evaluate the relative ability of OZ vs. conventional instruments in remaining accurately centered in both the localizer and glide path guidance beams of an ILS during an approach under low-visibility conditions. The narrow ILS localizer beam shows the pilot whether the aircraft is precisely on, or to the left or right of, the extended runway center line, while the equally narrow glide path beam indicates whether the aircraft is on, or below or above, the correct descent path to the runway. An ILS approach is one of the more demanding procedures for pilots, who also will be making a steady descent, lowering undercarriage and flaps, adjusting the trim, monitoring the radio for signals denoting passage over the middle and inner ILS marker beacons, talking to ground controllers, and maintaining the correct approach speed. Nevertheless, these tasks become quite routine for most pilots and, apart from turbulence, windshear and other factors, the process is fairly straightforward under normal conditions.

In the test, however, a key element was changed. While the subjects flew three approaches on the separate OZ and Cessna simulators at a leisurely 85 knots, typical of the Cessna’s normal performance, they also flew an equal number at twice and at four times that speed, at 170 and 340 knots. At those speeds the slightest deviations off the localizer and glide path had to be instantly corrected to prevent gross departures from the approach path, with the risk of having to conduct a missed approach. The corrections also had to be precise: overcorrecting would cause a deviation in the opposite direction. And on the glide path, that could develop into a potentially hazardous roller coaster effect as the aircraft got closer to the ground.

Throughout the tests extensive data on localizer and glide path deviation, airspeed and position was collected at a 57-Hz rate. When analyzed, the data showed that at all three approach speeds, OZ provided at least 50 percent tighter adherence to the center of the localizer and glide path guidance beams than did the Cessna’s conventional instruments, even though the test subjects had spent most of their careers flying dial and pointer displays.

Much of this improved accuracy was attributed to the pilot’s instantaneous, and virtually instinctive interpretation of the OZ display via both focal and ambient visual channels. It compared favorably vs. the sequential, more time consuming, conventional instrument scan technique, via the focal channel alone, necessary to build a mental picture of the ongoing situation.

There was, however, one initially puzzling test result. There was no significant difference between the OZ and Cessna data vis-a-vis the ability to hold the required airspeeds throughout the procedures.

Still concludes that this could suggest the need to modify OZ airspeed symbology, which uses expanding and contracting vertical bars between the upper and lower "wings" of the display. True, the results showed that the vertical bars worked as well as the conventional airspeed indicator. But OZ’s design goal is to provide much superior situational awareness, rather than equivalence to current displays.

Benefit to Helicopter Pilots

Still and Temme also have optimized the system for precise helicopter hovering under instrument conditions, a mode that is virtually impossible with current rotary wing instrumentation. Here instrument conditions mean not only low cloud or fog, but the blinding, zero-visibility conditions encountered when rotors pick up dust, sand or snow close to the ground. Still points out that OZ, uniquely, has the inherent ability to provide instrument hover guidance. OZ also allows helicopter pilots to exactly arrest their vertical descent rate when performing a critical autorotation following an engine failure in zero-visibility conditions, a major safety benefit. Similarly, the OZ display greatly eases the task of flying the otherwise delicate "pedal turn" maneuver, where the machine circles around, while remaining pointed at, a specific location on the surface below, precisely maintaining its height above the ground.

The researchers had hoped to install OZ in a general aviation aircraft cockpit this year, where it would replace the right hand instrument panel and allow "real world" system testing. Unfortunately, this was not possible, but Still is aiming to launch the effort in 2006.

Interpreting OZ

The OZ flight guidance display is startlingly different from the conventional instrument panel installed in the Cessna 172. Both are simulations and were photographed simultaneously at the University of West Florida’s Institute for Human and Machine Cognition during a test exercise. Both therefore display identical flight conditions.

The easiest way to understand OZ is to first look at the Cessna’s instruments and then relate them to the OZ presentation.

In the photos on the previous page the Cessna’s artificial horizon shows that we are in a very slight left bank, and its altimeter, to the right of the horizon, indicates an altitude of 2,000 feet. These are mirrored by the bright red horizon line now slightly tilted across the full width of the OZ display and showing 2000 at either end. The Cessna’s compass, below the artificial horizon, indicates a heading of 070 degrees, as does the heading indicator at the top of the OZ screen. Looking ahead through the Cessna’s windshield, we see that the airfield is off to our left, although it is difficult to discern the actual orientation of the runway at this distance. OZ provides this with its three green dots, analogous to runway approach lights, which allow us to easily and correctly position ourselves for a landing.

But we are still quite high for an approach, and so the aircraft is descending rapidly, as shown by the Cessna’s vertical speed indicator, to the right of the compass, which indicates a descent rate of over 2,000 feet per minute. OZ tells us this more precisely, showing, to the right of its two vertical green bars, that our actual rate of descent is 2,120 feet per minute. But with OZ we can instinctively recognize the unusual descent rate by simply seeing that its center "bulls-eye" is well below the red horizon bar.

In normal straight and level flight, the bulls-eye would be centered on the horizon bar, while raising the aircraft’s nose to place the bulls-eye above, but touching, the bar would give us a pre-set climb rate. Conversely, placing it below, but still touching the bar, would produce a pre-set descent rate. At all times, in fact, the OZ bulls-eye shows us the aircraft’s precise inertial path.

We also have reduced power for our descent, although the Cessna’s engine instruments are outside the right-hand edge of the photograph. (This fact does, however, illustrate the extent of a conventional full instrument scan.) But we can see the Cessna’s airspeed indicator, to the left of the artificial horizon, which reads around 110 knots. At the top of its two vertical green bars, OZ tells us that we are actually flying at 111 knots. But the length of those green bars confirms that power is reduced, and if we wish to stop our descent and resume level flight, increasing power will cause the bars to extend until their tips touch the yellow gull wings. At this point the exact amount of power is being produced to maintain level flight at the chosen airspeed.

The gull wings are extremely sophisticated indicators of several flight characteristics, most too detailed to describe here. But rolling the aircraft into a turn and placing a wing along the horizon bar put the aircraft into the precise 30-degree bank used in instrument flight procedures.

Finally, although not well illustrated in the opening photos, the quite unique OZ "star field" consists of points of light throughout the screen that converge at its center. Reminiscent of Star Trek’s Enterprise entering warp speed, but very much slower, the star field’s movement past the aircraft provides an overriding sense of aircraft attitude, allowing swift and correct recovery from even the most severe turbulence or control upset. A brilliant safety concept, the star field could unquestionably have saved many lives in the past.

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