Influencing every aspect in the sky
The 1992 Robert J. Collier Trophy — the award honoring the greatest achievement for the advancement of aviation or aerospace for the year — went to the team that developed the Global Positioning System (GPS). Naval researchers joined forces with the aviation industry, the computer industry, and the U.S. Air Force over the course of 20 years to build GPS. Fourteen years later, there is no question that GPS deserved every morsel of the attention and effort given it by such a diverse collaboration. GPS influences every aspect of aviation. Heck, it's even in your car — or boat — or tractor.
GPS comprises at least 24 satellites circling the planet at an altitude of approximately 11,000 miles, along with the ground-based facilities necessary to monitor and control the satellites. Additional satellites provide a backup in case a satellite in the network goes offline. Pilots operate handheld or installed GPS receivers that acquire signals from several satellites and use the precise time it took for the signal to travel from satellite to receiver to determine the aircraft's position.
Whether you fly nap-of-the-Earth VFR or the latest instrument approaches, GPS is a tool you can use to make your flying safer. For a long time, general aviation pilots had the best of it — those commanding airline cockpits (complete with inertial navigation systems and capable autopilots) lamented for (or carried in their flight bags) the handheld GPS units soon ubiquitous within GA aircraft by the late 1990s. And as panel-mount, IFR-fluent navigators grew in power and ability, once again we reaped the benefits first, with GPS overlays for existing instrument approaches, as well as the first systems to use WAAS (Wide Area Augmentation System) for precision approaches where no ILS could go. WAAS also has helped to deliver vertical guidance for nonprecision approaches — with minima depicted as "LNAV," yet with a navigator-generated glide-slopelike needle to assist you in establishing a stabilized descent.
A single-source, standalone navigation system — and one that doesn't rely on line-of-sight, ground-to-airplane signals — makes precise position knowledge possible, and the portable GPS solutions make this possible in every cockpit. Improved situational awareness is the result, whether backing up traditional navigation procedures such as pilotage or being used during an emergency to assist the pilot.
What's next for GPS? Already used for fleet tracking and for flight data recording (one program allows users to review a flight in detail overlaid on high-resolution satellite imagery), the future applications of GPS seem limitless. One test application is under way in the busy Manhattan airspace: High-density helicopter routes made possible by GPS may bring order to the congestion.
Manufacturers also will continue to address concerns about the complexity of GPS navigation units. An "undo" function, similar to that in PC-based programs, is viewed as prohibitively difficult to implement in the aviation environment. However, user interfaces should lead the pilot through steps, giving appropriate and regular feedback to the pilot, and staying away from requiring the pilot to memorize a long list of button presses to make the box do what the pilot wants it to do. If the pilot doesn't have to read a dictionary-size handbook to use the navigator, that's even better.
In the end, it's WAAS that's going to take GPS to the next level, from its immediate benefits in integrity to the approaches made possible by its implementation around the world (see " Wide Area Augmentation System [WAAS]," page 78). And users around the world, though they can use the North American GPS in a limited fashion, will benefit from increased development worldwide of the Global Navigation Satellite System, with regional satellite networks planned to augment the current GPS. — Julie K. Boatman, Technical Editor
