Seeing Is Believing
Illustration for TIME by IAN EVANS
Friday, Apr. 12, 2002
Landing at Amsterdam's Schiphol Airport isn't onerous for pilots, because it's situated on very flat land. A plane's Instrument Landing System works beautifully there because the ground is mostly horizontal. But landing at Geneva Airport, which sits in bowl surrounded by mountains, is another matter--particularly if bad weather has created a low ceiling.
The current system relies upon a dial with two needles that the pilot must keep centred while trying to maintain visual clues from the outside. "It's very intense," says Eric Theunissen, an associate professor of electronic engineering at the Delft University of Technlogy in the Netherlands, and head of its avionics education program. When a pilot is working that hard, "he is much more vulnerable, especially in mountainous areas." And even more so if something else goes wrong, like a failed engine or a need to divert from the flight plan.
Theunissen's group, over the last decade, has designed a so-called "tunnel-in-the-sky" navigation data display system that helps pilots negotiate complex landing paths, particularly in mountainous regions. As far back as 1952, U.S. Air Force engineers had the idea for just such a system, but only recently has the needed technology become available.
Even in the early 1980s, Theunissen says, it would have taken "enough computing power to fill an aircraft" to run the system. But since the early '90s, thanks to chip technology, there has been enough off-the-shelf components to bring the system to fruition.
For the synthetic vision display to work, it must accurately know where the plane is located. That's accomplished by using the satellite-delivered Global Positioning System (GPS) in conjunction with the conventional, onboard positional determinate system. It must also know where the obstacles are. This information comes from several databases, including the World Encompassing database that offers a high degree of resolution. Eventually, it will also tap into a forthcoming, even more detailed topography database created in 2000 during a Space Shuttle mission. Finally, the system must be able to use all that data to safely direct the pilot from where he is to the runway. This is where the tunnel-in-the-sky graphic display comes in.
What a pilot sees on a screen is an approximation of the landscape with a purple square overlaying it. Trailing off behind that square is a tunnel-like series of white squares that decrease in size. The plane is represented by a simple icon of a circle with a tail and wings. As the pilot steers his aircraft, he must keep the icon within the tunnel. The system's been tested over the past year at a NASA base in Langley, VA, and at the Eagle/Vail Airport in the heart of the Colorado Rocky Mountains. Pilots give it two thumbs up, saying it makes even the most complex, curved approaches easier and less stressful.
Theunissen says he expects the tunnel-in-the-sky display will be phased into upcoming generations of aircraft within about five years--finally making a reality what aerospace engineers of 50 years ago could only dream of.
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