The next generation of air traffic control

By J.R. Wilson

Researchers from the FAA, NASA, and industry are putting together the first phases of Free Flight—a fundamental shift in how commercial air traffic flows over U.S. airspace and throughout the world. Much of this effort revolves around how to move as much responsibility for air control from the ground and into the aircraft themselves. Time will tell if this approach can work.

The Raytheon Air Traffic Control center near Oslo, Norway expanded defense technologies to air traffic control.

Almost everyone these days has a horror story to tell about airline travel. Late departures and arrivals, cancelled flights, and missed connections — all because of delays on the ground or in the air — are making commercial air travel a bigger headache with each passing year. Experts point out that airline flight delays are likely to get worse before they get better. The reason, they say, is an air traffic control (ATC) system that is nearing, or in some cases has reached, the saturation point, with no letup in sight for demand for air travel.

Air traffic officials in the U.S. Federal Aviation Administration (FAA) in Washington, however, have a program in place to alleviate some of the ATC bottlenecks that lead to rippling delays that reach across the country, and sometimes even across the world. This program is called Free Flight, the aviation industry-conceived and FAA-supported effort to share air traffic control (ATC) data efficiently among all players.

FAA officials, in fact, are already calling Free Flight a success. "We're on schedule with all Phase 1 programs — ahead of schedule, actually," says FAA Free Flight deputy director John Thornton, on the initiative to reduce flight delays and improve costs and efficiencies in air travel.

Two components of Free Flight are finished, Thornton says — the surface movement advisor, also known as SMA, and the collaborative decision-making component, or CDM.

The CDM "is like an internet for aviation," Thornton Says. It enables FAA officials and the airlines to trade real-time information with which they can make tactical decisions on mitigating delays. CDM provides airline operations centers and the FAA with real-time access to National Airspace System (NAS) status information, such as weather, equipment availability, and delays. It also uses two other primary components — ground delay program enhancements and initial collaborative routing.

The SMA, meanwhile, provides aircraft arrival information to airline ramp towers. With this information, airline officials can improve how they manage ground assets such as gates, baggage operations, refueling, and food service.

Three other toolsets that comprise the total Phase 1 charter are:

• User Request Evaluation Tool (URET), which enables air traffic controllers to identify potential conflicts among different aircraft flight paths as far in advance as 20 minutes;
• Traffic Management Advisor (TMA), which enables en-route controllers and traffic-management specialists to develop arrival sequence plans for selected airports; and
• passive Final Approach Spacing Tool (pFAST), which makes the most of runway space by sequencing aircraft runway assignments according to user preferences and system constraints;

"TMA is at four en-route traffic control centers, with two more to go and they are on schedule," Thornton says. "The passive FAST is in three terminals now — Dallas/Fort Worth, Los Angeles, and Atlanta — with two more to go." Phase 2 will install five more TMAs, yet FAA officials are holding off on a decision to deploy pFAST tools until sufficient structure is in place to support it.

The pFAST system requires a Standard Terminal Automation Replacement System (STARS) platform, "and we don't have that quite deployed yet," Thornton says. "Instead of starting something that has a dependency we're not certain of in terms of deployment, we just defer it. But we don't expect to miss milestones in Phase 2.

FAA officials have installed prototype URET systems at major airports in Memphis, Tenn., and in Indianapolis. In addition, "we are engineering it for a production-quality integrated tool that will go out to seven centers by the end of this year," Thornton says. The URET is helping to save airlines that operate in the Indianapolis and Memphis airspace about $1.5 million a month, he adds. "The controllers have really taken to the tool. Direct routing is up 40 percent since the prototypes went into place."

URET has additional benefits, according to scientists at the MITRE Corp. For example, the system introduces a dynamic, four-dimensional trajectory-based strategic conflict probe to help control en-route traffic at the sector level. Since its installation at Indianapolis and Memphis, URET has recorded more than a half million operational hours.

• SMA is used in the takeoff and landing phases of flight and provides taxi times and gate delays;
• CDM helps in the takeoff, departure and cruise phases, providing an overall strategic picture by providing data of the National Air Space status;
• URET comes into play in the cruise and the descent phases of flight;
• TMA meters aircraft during descent; and
• pFAST comes into its own during aircraft final approach.

Although Free Flight Phase 1, begun in 1998, does not conclude until 31 December 2002, Phase 2 got an early start in October 2000. With Phase 2 comes the Controller Pilot Data Link Communications (CPDLC), which will begin to involve equipment installed in aircraft cockpits.

The Standard Terminal Automation Replacement System ? or STARS ? display is part of an FAA and U.S. Department of Defense program.

"Right now we're starting at Miami, where we expect to have an initial [CPDLC] system in place in 2002," Thornton says. "That will have more services and will involve just American Airlines — 28 aircraft — so we can work out some of the computer/human interface issues, both in the cockpit and on the ground."

Much of the developmental work on CPDLC has been at MITRE's Center for Advanced Aviation System Development (CAASD) in McLean, Va., an FAA federally funded research and development center. The CPDLC Build 1 at Miami will be an 18-month effort involving data rather than voice channels to upload a limited number of services — such as altimeter settings, predefined informational messages, voice frequency assignments, and initial contact altitude verification. Data will flow directly to airliner cockpits via the ARINC Very High Frequency (VHF) Digital Link Mode 2 (VDL-2) as the air/ground subnetwork.

After that will come Build 1A, a national rollout of those services plus giving controllers the ability to uplink clearances (altitude, speed, heading, and route) to pilots, and for pilots to downlink requests for specific flight levels to air traffic control.

The required ground infrastructure to implement the full CPDLC capability nationwide is scheduled for completion in 2005. The Free Flight program expectation is that moving much of the routine controller-pilot communications with CPDLC-equipped aircraft from voice to data channels will substantially reduce the impact of aviation traffic growth on already congested voice frequencies.

According to MITRE, the CPDLC end-to-end architecture can be split into the following portions:

• the en-route ground automation portion, providing CPDLC and all supporting applications and interfaces to controllers. This includes the Data Link Application Processor (DLAP), the Context Management Application (CMA), the Host Computer System (HCS) and Display System (DS), and Air Route Traffic Control Center (ARTCC) communications infrastructure;
• the FAA's ground Aeronautical Telecommu-nication Network (ATN), which provides connectivity to ATN applications at different sites and connections to the air/ground service providers (the FAA's Wide Area Network (WAN) serves as subnetwork to ATN and provides all other non-ATN connectivity);
• the air/ground service provider networks that provide connectivity to aircraft; and
• the aircraft avionics, which process and display information to the pilots.

For Block 1A, application processing and display happen in the DLAP and DS, with the HCS acting as a pass-through for DLAP-DS communication. Two geographically redundant national CMA systems will serve all DLAPs. The FAA's ATN backbone will include five nodes; an Internet Protocol (IP) subnetwork is planned to interconnect the ATN routers.

Another Phase 2 capability from MITRE, which is getting an early start, is the collaborative routing and coordination tool (CRCT). This is an integrated collection of automation functions that help controllers:

• monitor traffic flow;
• alleviate congestion;
• avoid severe weather; and
• analyze how the flight plans of individual aircraft can influence entire NAS sectors.

Eventually, that same information also would be available to the airlines and in-flight aircrews.

During the last two years, CRCT has been under evaluation at the Kansas City Center, while the Air Traffic Control System Command Center, which is responsible for national traffic flow management, was installed earlier this year at the Indianapolis Center.

Much of the technology FAA officials are deploying in Phase 1 — and partially in Phase 2 — came from work at NASA and other parts of MITRE, Thornton explains. "What we've done is short-circuited the normal deployment timeline," Thornton says. "We've worked closely with the controllers union so they are helping us get the promising tools out that have some functionality they can use. We will spiral out from that, adding functionality as it becomes available. We're not going for the home run—we prefer hitting singles and doubles and having no surprises."

He says leaders airline and government leaders who are part of the international aviation community are judging development so far with a "very positive reaction." Many of these officials have details of the program's progress and have traded information with the FAA on potential technologies and other developments.

The Raytheon Precision Runway Monitor System uses scanned radar for parallel runway approaches to increase capacity and enhance safety.

Free Flight is an integral part of the FAA's NAS Operational Evolution Plan, which calls for widespread use of Free Flight tools as part of the plan's 2002 to 2004 mid-term solutions to growing air traffic congestion and delays. In a 30 May 2001 executive summary, FAA officials forecast that as many as 800 more commercial flights will be airborne at any given time during standard operating hours than at the present time — an increase of about 30 percent.

"The key driver for en-route capacity is the ability of the controller to direct aircraft, when needed, by vectoring traffic, changing altitudes, or exercising speed control," the summary states. "The targeted improvements for en-route airspace provide substantial reductions in interactions between flights and in communications workload, thus reducing the number of controller-to-pilot directives."

A big part of the development of Free Flight was the aviation community's insistence on a single point of contact with the government. That task recently fell to newly named program director Bob Voss.

"The goal of Free Flight is to increase capacity and efficiency without diminishing safety," Voss says. "The bottom line, though, is that Free Flight was conceived and requested by the aviation community. They told us what they wanted, where they wanted it, and when they wanted it. There are no surprises here; we're providing what was asked for. The new approach — build a little, test a little, deploy a little — allows the FAA to avoid the large-scale modernization problems of the past. By delivering on time, which we are, we're setting a model for the future."

A stated long-term goal of Free Flight always has been to move as much of the air traffic control effort as feasible from the ground into the cockpit. This approach, for example, would give pilots control over their routes. It also would enable the aircraft, rather than ground radars and controllers, to set and maintain safe en-route separations between aircraft. The system currently still follows standards set in the 1950s calling for five miles lateral separation in the en-route environment, three miles lateral separation in the terminal airspace, with 1,000 to 2,000 feet vertical separation, depending on altitude.

"That has always been the long-term goal," Thornton says. "Right now we're moving from a rigid to a flexible flight environment that could possibly transition some of these activities to the cockpit. The real focus of Free Flight right now, however, is getting newer and better equipment to the controllers."

The tools that Free Flight engineers are developing today do not yet require upgrades to the cockpit, he says. "What we're really doing is providing a lot of controller support tools. We're getting better equipment to the controllers faster today than we ever have in the past. A large reason for that is because we developed a close relationship with the controllers and the technicians' organizations and have worked quite closely with them."

There is no doubt that reaching the ultimate goal of moving some air traffic control tasks into the cockpit will require equipment changes and additions in airliner. For now, however, Thornton says whether that should be optional or required is a policy decision that has not been made:

"The airlines are trying to make a business case for themselves, optionally, but there's no point in having the datalink if there is no aircraft to communicate with. So it could become a requirement—or the airlines could see benefits and do it voluntarily, in which case some might not have it," he says. ""Free Flight is a new way of doing business, focusing on the customer and providing early benefits. It has never missed a milestone. What has allowed us to do that is our close working relationship with controllers and technicians and I think the other facets of the (FAA) will use the map we have drawn for successful deployment."

The controversy swirling in Washington over future use of GPS for air traffic control revolves around a report by the John A. Volpe National Transportation Systems Center in Cambridge, Mass.

"A major element of GPS vulnerability lies in the very low power that makes it vulnerable to jamming," the Center's report states. "GPS also is vulnerable to spoofing, broadcast signals with deliberately misleading information, and to unintentional interference.

Authors of the report point out that disruptive technology is increasingly available, effective, and easy to hide. Furthermore, countermeasures may mitigate the worst GPS disruption with a combination of strong GPS system and by integrating GPS with independent systems. "An important part of ensuring sufficient robustness in GPS-based systems is to provide these systems with adequate integrity monitoring," the report states.

The Presidential Commission on Critical Infrastructure Protection ordered the report, which recently went to the Assistant Secretary for Transportation Policy at the U.S. Department of Transportation.

The report could significantly alter the shape of the FAA's 15-year plan to make satellite-based navigation technology available for use throughout the National Airspace System (NAS).

Those plans incorporate GPS, originally developed by the U.S. Department of Defense, as well as proposed land- and space-based augmentations, such as Boeing's call for a new constellation of non-geosynchronous satellites that integrate communication, navigation and surveillance (CNS) capabilities.

GPS, augmented by one of those ground-based systems—the Wide Area Augmentation System (WAAS)—also is considered a key enabling technology in the FAA's Free Flight effort.

Satellite-based navigation also is integral to the FAA's Operational Evolution Plan (OEP), which looks to intermediate and long-term solutions to NAS capacity and delay problems. — J.R.W.

The current ATC system — including planned modifications — "simply will not provide the long-term capacity needed to allow uninhibited growth in air travel and aviation related economic activity," said John Hayhurst, president of Boeing Air Traffic Management (ATM).

Hayhurst made his comments in testimony in Washington July 19 before the U.S. House Science subcommittee on space and aeronautics.

An indirect cap on the growth of air travel because of infrastructure shortcomings poses a great concern to Boeing, he told Congress. Such a cap could sharply curtail the aerospace giant's projection of 18,000 new commercial aircraft in the next two decades — a massive market for which Boeing is in sharp competition with Europe's Airbus.

That concern led Boeing to create the ATM business unit last year and develop a proposed new space-based system that would address three major requirements to meet the projected traffic growth, according to Hayhurst:

• synthesize an airplane's position, altitude, speed, and intended flight path to improve how controllers manage aircraft trajectories;
• implement a common information network that links pilots and controllers with real-time information about aircraft trajectories, weather, and air traffic flow; and
• replace today's complex system of relatively small geographic airspace sectors with simplified, open, managed traffic flow.

"While the technical requirements and specific technological applications to accomplish these definitive features of our concept are still being developed, we believe that realization of this type of overall system can best be accomplished with an innovative, global system of satellites that integrates communication, navigation and surveillance (CNS) capabilities and functions," Hayhurst says.

"We believe that the on-board flight management systems will become a critical source of the information used by controllers for detecting and projecting airplane locations. And we believe high-speed, highly accurate data link type communications with greatly reduced voice communications will be the nervous system connecting the aircraft, the ground, and the satellites," he says.

Boeing officials claim their proposed satellite infrastructure would enable worldwide coverage for a next-generation air traffic control system, including many areas where insufficient infrastructure currently exists. Satellites would enable a global, integrated air traffic control system, Boeing officials say.

The concept features "trajectories"—the three-dimensional path an aircraft will follow—that make it possible to locate aircraft and predict where they will be with much higher precision and further into the future than ever before. Onboard systems would communicate intended flight profiles by two-way data links to air traffic service providers, while accurate space-based navigation and surveillance systems would enable flight crews to maintain extremely precise flight paths.

Boeing's plan received a boost in mid-July with Federal Communications Commission (FCC) approval of a license to use a portion of the 2 GHz mobile satellite services (MSS) spectrum.

"The FCC action is a critical step toward the development and implementation of the satellite-based element of our overall Air Traffic Management architecture," says Dennis Muilenburg, Boeing ATM vice president of engineering.

The license will enable Boeing to build a medium-Earth-orbit constellation of non-geosynchronous satellites operating in the 2 GHz band and augmenting the existing Global Positioning System (GPS).

Hayhurst called on Congress to pay for NASA's Aviation System Technology Advanced Research (AvSTAR) initiative to help design, model, and simulate the requirements and architectural concepts of a next-generation system. Boeing experts, he added, would contribute the company's own money to develop such a system and infrastructure. Boeing created a team of users, operators, equipment/service providers, and regulators to develop a system level set of technical requirements by the end of January 2002.

"One challenge to implementing a new system is the complex transition from today's system to a new operating paradigm," Hayhurst says. "This transition must ensure safe, efficient operations 24 hours per day, 365 days per year. Boeing has outlined a three-stage approach of gradually introducing the new features of the next-generation air traffic management system. Government and industry must do much more work to ensure that a comprehensive transition plan is developed."—J.R.W.