Winging It

Can Free Flight unjam overburdened airports?

7 min read
Winging It

This is part of IEEE Spectrum's special report: Always On: Living in a Networked World.

diagram showing Five software tools provide air traffic controllers with flight path predictions and aircraft status

Illustration: Steve Stankiewicz; Source: FAA
Tools for Free Flight: Five software tools provide air traffic controllers with flight path predictions and aircraft status at each stage of a flight--takeoff, cruise, landing, or parts in between--under the FAA's Free Flight Phase 1 Program.

SMA = Surface Movement Advisor: provides local airline operations centers with arrival information (mean taxi times, mean gate delay)

CDM = Collaborative Decision Making: provides central airline operations centers and air traffic controllers with data on weather, equipment availability, and delay

URET = User Request Evaluation Tool: provides en route air traffic controllers with predictions as to whether a plane will violate restricted airspace or minimum separation requirements with other aircraft

TMA = Traffic Management Advisor: aids en route traffic controllers by automatically developing arrival sequence plans for selected airports

pFAST = Passive Final Approach Spacing Tool: provides terminal radar air traffic controllers with aircraft sequence numbers and runway assignments, according to controller preferences and system constraints

Gridlock in the skies!" "Airport delays reach all-time highs!" "LaGuardia leads U.S. in airport delays!" Trying to fly anywhere last year seemed like an exercise in frustration and futility, as headlines screamed of record numbers of airport delays. It's a good bet that more are in store for travelers this year, too. Over the next decade, in fact, departures from U.S. airports are expected to rise 13 percent to more than 9.9 million annually, according to the Federal Aviation Administration (FAA), Washington, D.C. By 2015, airlines expect to carry twice as many passengers as they do today.

But help is on the way. The FAA believes that the solution to delayed flights is beginning to shape up. The agency is optimistic that its modernization plan and efforts to implement a program called Free Flight will go a long way toward solving the problem. Simply put, Free Flight opens the skies to air traffic, removing many of the enforced air routes that planes were required to follow. The program calls for air traffic controllers to continue to supervise flight operations and monitor safety measures.

But air traffic controllers, still using equipment that is decades old and breaks down frequently, are wary of FAA promises. They are also well versed in the vagaries that befall an agency dependent on congressional budget authorization to develop technology programs. "We'll be happy when better, more reliable technology reaches our hands, but we're not counting on it happening soon," was the consensus at a National Air Traffic Controllers Association meeting in Atlanta, Ga., in September.

The controller's labor group, headquartered in Washington, D.C., doesn't see the rampant delays going away anytime soon. Airports are not pouring concrete for additional gates or runways to accommodate the increasing number of daily flights. "As long as slots [rights to takeoff and land at an airport] are added and filled on already overbooked runways, the situation will be problematic," explained a New York City air traffic controller at the Atlanta meeting. Added an Orlando, Fla., controller: "There is a finite number of planes that can take off and land in a given time period on a length of runway. Adding planes doesn't improve the situation."

For a start, planned software upgrades are being installed to improve air traffic control systems. Upgrades in about half of the 20 en route centers in the United States, which handle aircraft at higher, cruising altitudes, have gone pretty smoothly, but there have been some mishaps. Witness the Host computer failures in the Los Angeles and San Francisco en route centers last October. Upgrades to the Los Angeles mainframe that processes radar returns for display as data crashed the system, taking hours to fix. Two weeks later, the same thing happened when the Bay Area center was upgraded. The two centers have gone back to using the old software while the problem is studied and a remedy found.

What will help the situation, and is already being tested in limited circumstances in certain air traffic facilities as prototypes, is better technology that will give controllers more reliable displays, computer systems, decision-support tools, and data--all goals of Free Flight, or at least of Phase 1 of the program.

Not a free-for-all

Free Flight has been bandied about since the early 1990s as a remedy for clogged U.S. air traffic systems. It allows planes flying under instrument flight rules to have comparable freedom of movement to those using visual flight rules. Situations that force pilots to fly by instruments, rather than by visual cues, often translate into a more restricted airspace for the pilot; his options are limited by what the instruments tell him, rather than by anything he can see. But the pilot using the Free Flight system also has restrictions. As an FAA spokesman emphasized: "Pilots would not have carte blanche to select speed, altitude, and flight path. Free Flight is not 'free for all' but the minimization or removal of air traffic restrictions that slow down the system."

Today, pilots fly a course relayed to them by an air traffic controller and set up by an airline dispatcher who designs a flight path after factoring in the weather, the fuel load of a plane, and the equipment scheduling needs of the airline. For example, instead of a more direct path, a dispatcher may route a plane from Monroe, La., north and east through Arkansas and Tennessee to reach Atlanta, Ga., to avoid a line of thunderstorms moving across Mississippi on the due east routing.

Under Free Flight, a pilot would determine the flight route with approvals and guidance from air traffic controllers along the way, all the while paying attention to weather and minimum vertical and horizontal distance between planes.

One current Free Flight program, already up and running because it was strictly procedural, is the Central Pacific Oceanic Program. In the airspace over the Central Pacific, advanced satellite voice and data communications allow for faster and more reliable transmission to enable reductions in vertical, lateral, and longitudinal separation among planes, as well as more direct flights and tracks and faster altitude clearances.

By 2005, because of advances in communications, navigation, and air traffic management, U.S. users in the Oakland Flight Information Region are expected to save US $35 million annually in aircraft direct operating costs plus $45 million in increased payload capability. Included in those totals would be a savings of 9000 hours in flight and ground time and 25 million gallons of fuel.

Making it work

For Free Flight to provide the right benefit, however, the procedures, systems, and technologies to prevent collisions in the air and on the ground must be fully implemented. What is needed, according to the FAA, will be ground- and air-based communications, navigation, and surveillance equipment; avionics; and automated decision-support systems. These, coupled with supporting procedures and systems, will enable straightforward coordination between airlines, pilots, and air traffic controllers.

"Today's airspace is designed with rigid, often inflexible routes," said Charlie Keegan, who runs the Free Flight Phase 1 Program Office for the FAA. "Facing airspace gridlock, our challenge is to find new and better ways to operate, to squeeze precious efficiency from our operators. Free Flight takes aviation to the next level without compromising safety. It's where aviation needs to go."

The Free Flight Phase 1 (FFP1) Program Office was established in October 1998 to deliver a handful of core capabilities as defined by RCTA Inc., Washington, D.C., a nonprofit organization that serves as an advisory body to the FAA. Those capabilities, embodied in five technologies, are to be in service in a few facilities by the close of 2002.

To meet a mandate from FAA Administrator Jane Garvey to achieve the RTCA industry-recommended goals, Keegan and his staff opted for a phased implementation that produces incremental improvements at each stage of the program. "The FAA's air traffic control modernization programs have been criticized--not altogether unfairly--for swinging for the grand slam. Phase 1 is about singles and doubles, delivering what controllers need, and delivering it on time," noted Keegan.

That approach translates into the development and testing of prototypes in one or two facilities, followed by deployment of Build 1 (FAA-speak for the official version 1 of hardware and/or software) in a handful of facilities. Rollout to other facilities will follow. The idea is to make incremental improvements continuously with immediate benefits that boost efficiency within the air traffic control system from the get-go.

To do that, FFP1 is embracing five software tools for planes in various flight stages [see figure, top of page]:

  • For planes in initial ascent to cruise altitudes, the Collaborative Decision Making (CDM) tool provides airline operations centers and the FAA with real-time access to National Airspace System status information, including weather, equipment availability, and delays. The idea is to exchange information with the airlines as closely to real time as practical, so that air traffic controllers may alleviate airspace congestion.
Free Flight Phase 1 is about delivering what controllers need, and delivering it on time

According to Satish Mohleji of Mitre Corp., Bedford, Mass., two of the three Phase 1 capabilities for CDM--initial collaborative routing and ground delay program enhancements--have been fully deployed and "are no longer prototypes." The infrastructure for the third, exchange of National Airspace System status information, should be done by June of this year.

  • For planes at cruising altitudes, the Traffic Management Advisor (TMA) gives en route controllers an automated capability to develop arrival sequence plans for selected airports.
  • Also for planes at cruising altitudes, the User Request Evaluation Tool (URET) is a conflict probe, developed by Mitre Corp. and implemented by Lockheed Martin Corp., Bethesda, Md. It enables controllers to manage pilot requests for altitude and route changes in en route airspace (cruising altitudes) by identifying potential aircraft-to-aircraft conflicts as far ahead as 20 minutes. It also predicts whether an aircraft will violate minimum separation requirements with another aircraft or restricted airspace, eliminating potential conflicts before the situation requires tactical maneuvering by the pilot.

Prototypes are undergoing operational testing at Indianapolis and Memphis air route traffic control centers. URET Build 1 will be tightly integrated with the new display consoles now in place at FAA en route centers. Detailed design was completed last August. By the end of January, the software for this first post-prototype will be handed off to integration and test teams. By December, it will be in use in Memphis and Kansas City, with an initial rollout that same month to five other facilities that handle aircraft flying at higher altitudes.

  • For planes descending into final approach, the Passive Final Approach Spacing Tool (pFAST) maximizes runway use by providing terminal radar controllers with aircraft sequence numbers and runway assignments, according to preferences and system constraints.
  • For planes taxiing to and from airport gates, the Surface Movement Advisor (SMA) gives airlines aircraft arrival information to assist them in managing ground assets, such as gates, baggage operations, refueling, and food service. With development completed in December 1999, SMA was made available at six airports: Chicago O'Hare, Dallas/Fort Worth, Detroit, Newark, Philadelphia, and Teterboro, N.J., after prototype trials at Detroit and Philadelphia.

Next for Free Flight

Concerned that momentum established would be lost and a gap would occur after Free Flight Phase 1 ends on 31 December 2002, FAA Administrator Garvey named John F. Thornton to direct Free Flight Phase 2, which will put Phase 1 tools in more facilities. Phase 2 efforts will be directed toward communications, navigation, and surveillance equipment.

Though still on the drawing board, Phase 3 is expected to last from 2006 to 2015 and complete the rollout of the hardware, software, and other results of the first two phases. Funding allocations to date, however, run only through a portion of the expected Phase 2 duration. Last March, Congress passed the Aviation Investment and Reform Act for the Twenty-first Century. Known as AIR 21, it authorizes $40 billion for the FAA over a three-year period, ending in 2002. Phase 2 is expected to end in 2005.

To Probe Further

The National Air Traffic Controllers Association maintains a Web site at, with regular updates about safety and technical issues.

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