The future—today

Welcome to High Desert Tracon, one of the 185 civilian terminal radar approach control facilities under the aegis of the FAA in the U.S. air traffic control system. Unlike most air traffic control facilities, the main control room here, on Edwards Air Force Base in California, does not look like a relic from an old war movie. It resembles instead the flight deck of the Starship Enterprise [Fig. 3, middle].

At every controller workstation is a high-resolution 2048-by-2048-pixel Sony 20-inch color monitor [Fig. 4]. Colored text distinguishes the planes being handled by the controller at that workstation (cyan) from planes in the area being handled by other controllers (green), and identifies hand-offs, which are transfers of responsibility from one controller to another (white), and emergencies (red). The workstation allows controllers to bring up maps directly on the display from a large and expandable database, or to draw their own.

Controllers can also use touch panels on the right and left of the display as function keys to facilitate theirtraining.

But probably the most important feature to the controllers is that, unlike the PVDs and DEDs, these graphics display processors (GDPs) do not go blackbecause of frequent internal failures or problems with the computers that process radar information. Data collected from 10 radars sited to monitor the Tracon's vast airspace is fed to a bank of 30 networked workstationsbuilt by Sun Microsystems Inc., Mountain View, Calif. If one of the Sun workstations fails, the system may degrade as the other units are stressed, but it does not go down.

The road from the PVDs previously in use at High Desert Tracon to the graphics display processors of today was, compared to most air traffic control system upgrades, a smooth and short one, thanks to the air traffic control facility's unique position as a joint civil and military responsibility.

Although identified as a terminal radar approach control facility, High Desert Tracon is somewhat of a hybrid, having some characteristics of an en route center. It covers a far greater airspace than typical Tracons, with 25 000 square miles, in contrast with less than 1000 square miles.

In addition to handling approaches and departures for five airports—Palmdale, William J. Fox, andSouthern California International, along with Edwards Air Force Base and the Navy's China Lake facility—it acts like an en route center by directing civilian traffic passing through its airspace, routing it if necessary around restricted airspace reserved for the Department of Defense. It also coordinates closely with military air traffic control facilities nearby, passing airspace into Navy and Air Force control when necessary for military maneuvers and taking it back when those operations are completed.

High Desert Tracon also used a different radar information processor. Other Tracon facilities in the United States today use ARTS, resolving targets and feeding the resulting radar data and some flight information to the displays. But the original ARTS systems were configured to accept only one radar feed. (ARTS is a special-purpose Sperry computer manufactured in the '70s; later versions can accept multiple radars.)

Since High Desert Tracon's extensive airspace has long required multiple radars, the facility back in 1981 was assigned a Mosaic direct access radar channel (M-DARC) computer as a radar processor. Similar DARC computers, produced by Raytheon in the late '70s, are used at en route centers as a backup for the main Host computers at the centers. DARC can handle multiple radars, but it is purposely limited in order to be effectively "bullet-proof" and able to always work in an emergency—it lacks the conflict alert and minimum safe altitude warning functions and is unable to manage automated hand-offs.Until recently, High Desert Tracon simply did without those controller tools.

Tracking military activity

While High Desert Tracon was experiencing problems similar to those of other air traffic control facilities—failing PVDs and a central computer at its maximum (adding a new feature meant deleting an old one)—it had one additional problem not faced by the others. The DARC system was simply not capable of accurately tracking the high-performance military aircraft whizzing through High Desert Tracon's airspace.

Since this last failing was, in essence, a Department of Defense (DOD) problem, even though one faced by a civilian facility, High Desert Tracon in 1988 turned to the department for a solution. In 1989 the Tracon was granted funding for a conceptual design and functional specification, said Robert Cox, a technical consultant to the DOD, who was assigned to High Desert Tracon from Computer Sciences Corp., in Falls Church, Va. Full funding for the basic system was granted in 1991, and the actual design effort began in September of that year, with BDM Air Safety Management Corp., a unit of BDM International Inc., McLean, Va., chosen as the contractor. The project was tagged "Rehost."

The development process turned out to be a textbook case of how to design an air traffic control system for the '90s. According to a recent publication bythe National Transportation Safety Board, "The ingenuity associated with development of the High Desert Tracon system deserves consideration as a model for future air traffic development and procurement programs."

"They did it right," said Steven Zaidman to Spectrum. "They involved controllers at every stage." Zaidman is director of systems architecture and investment analysis for the FAA.

Explained Phillip Stange, airway facilities manager for Edwards Air Force Base: "We did not go to a vendor and buy hardware, as the FAA does. We wanted to get the software done, and then figure out what to run it on." (The decision to use Unix workstations was made early on.)

The baseline system cost $10.8 million; the second software release, an additional $1.7 million; and the third software release, now being implemented,$2.3 million more. These figures include the cost of all hardware, software development, documentation, testing, and training for High Desert Tracon and for two military control facilities on Edwards Air Force Base.

At the start, the Western/Pacific Region of the FAA and the Department of Defense immediately established a product team that included representatives from the controller workforce, the FAA and DOD maintenance workforce, and Tracon and DOD management. The team started prototyping systems and testing the interface on controllers assigned to the facilities.

The input from these people led to the addition of touch screens to accelerate training and thus smooth out the transition from old to new systems. Their recommendations also resulted in a forgiving system for entering flight plan information (previous systems would reject information—like the call sign of an aircraft, itsassigned altitude, or aircraft type—if controllers failed to key it in according to a predetermined order) and the color switch to cyan from a darker blue that was used initiallyfor crucial aircraft information (the darker blue proved to cause eye strain).

Because controllers were involved in the design process throughout, acceptance when the system was complete was immediate. "We told the workforce," Stange said, "that if they wanted something upside down and purple, we'd give it a try."

Input from controllers continues today. Their suggestions are collected in a binder available to all, commented on, and then discussed by the Rehost configuration management board, representing facility management. Changes agreed upon are passed on to software developer BDM and to local system specialists, FAA employees who handle software maintenancefor inclusion in a future software release. (Air traffic control software at other FAA facilities may be changed only in minor ways, if at all; faced with massive, complex code written in ancient languages, some systems specialists are fearful that significant changes would bring the entire system down.)

From Host to Rehost and Ollie

One of BDM's key contributions, according to Robin Deyoe, BDM vice president, was a high-speed aircraft tracker design, adapted from a radar tracker that BDM had created for a classified Department of Defense program. Current FAA radar processors use a single radar chosen from a predefined set of radars to monitor each aircraft. Each of these radars updates itselfapproximately every 6 seconds in the Tracon environment, 12 seconds in the en route center environment.

The BDM system takes information from multiple radars updating at different times, each with varying inaccuracies, and uses a Kalman filter algorithm to combine varied radar inputs to distinguish the true position of the aircraft. (A Kalman filter is a method for providing an optimal estimate of variables in the presence of noise by generating recursion formulas.)

The resulting software, called Rehost, is written in C. The first version's capabilities were equal to, or better than, those in standard FAA systems, and followed defined protocols for information transfer between FAA facilities. It was certified by the FAA in 1993. Currently, the third major software upgrade of Rehost is being mounted.

The switch to commercial off-the-shelf equipment required a sea change in the way acquisitions are conducted, Spectrum was told byHigh Desert Tracon's Stange. Instead of procuring a huge computer, installing it, and leaving it in place for 20 years, purchasing off-the-shelf equipment required constantly upgrading it—manufacturers cannot be expected to support any one piece of hardware for more than five years.

"If you were going to install hundreds of these, from coast to coast, it'd take three to four years," said Brent Shively, air traffic manager for High Desert Tracon. "And as soon as you were done, you would have to go back to the beginning and start upgrading immediately." High Desert Tracon is now upgrading its Sun MicrosystemsSparc 470 workstations to Sparc 1000s.

While High Desert Tracon's Rehost has indeed proved to be successful, it is not the only modern air traffic control system in existence in the United States. There is also Ollie.

Ollie, Spectrum has learned, is a PC-based air traffic control display, developed secretly by engineers at the FAA's Atlantic City, N.J., technical center. Like Rehost, it uses a Sony 20-inch color monitor, and is reportedly a drop-in replacement for displays at facilities that use the ARTS-IIIe computer (the top-of-the-line ARTS system). It is called Ollie after Oliver North, because it is kept in back rooms and is not expected to see the light of day. Said James Allerdice, National Safety Commit tee chairman of the National Air Traffic Controllers Association (Natca): "[Ollie] is fieldable and attainable now, but it is politically incorrect."

There is also a PC-based controller workstation in operation at Washington National Airport, installed to improve surveillance of the sky over the White House after the crash on the south lawn of a Cessna 150 private aircraft in September 1994. "This screen doesn't fail," unlike the displays used in the rest of the facility, one of the Washington National controllers told Spectrum. "We've heard the FAA has more of these systems in storage. We tried to get them, but they said no." The FAA's Planzer responds that this system is monitoring airspace that is only several acres in size. "To extend that to say it could be used to control 1000 square miles is a quantum leap," he said.

None of these solutions may be right for all U.S. control facilities. Rehost's users stress that it is a site-specific solution, and would certainly require adaptation to other sites if rolled out on a system-wide level. "This is not a complete system," Shively said. "It is an evolving system. It is not an answer to everything, but it is not a bad start."

Meanwhile, replacements for the displays at the other U.S. control facilities are planned. They are of two types. One is the display system replacement (DSR) being developed by Lockheed Martin Corp., Bethesda, Md., for en route facilities. This system will replace the dumb PVDs with smart workstations but will leave the radar processing computers untouched. The other is the standard terminal automation replacement system (Stars) for terminal radar approach controlfacilities, being developed by Raytheon. Stars will replace both the displays and the radar processors with a distributed computing system.

Whether these systems will be as good or better than Rehost or Ollie is subject to debate. Both arose from the dismantling of the Advanced Automation System program, a more-than-10-year effort that was restructured by former FAA administrator David R. Hinson.