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Monday, October 1, 2001

Free Flight: So Far, So Good

Wouldn’t it be great if Free Flight suddenly and miraculously appeared? That’s not going to happen. But the "build a little, test a little" approach appears to be a workable substitute.

Adrian Gerold

Several years ago at an air traffic control (ATC) conference, a Boeing representative included in his presentation a slide that showed the transition from the crowded, delay-stricken skies of that time to the smooth, orderly air traffic flow of the future. The slide showed how Free Flight would allow many more airplanes to fly effortlessly in all directions. A large arrow on the slide led from the chaotic present to the calm future. But between the present and the future, the arrow passed through a white cloud that framed the words, "A Miracle Happens."

Many in the audience clearly felt that such a transition would, indeed, require a miracle. Fortunately, most caught the speaker’s tongue-in-cheek message: While Free Flight would be a major challenge, a miracle wasn’t really mandatory. Patient slogging by the total community could achieve the desired result. In fact, an overnight "big bang" switch to the broad range of new technologies required for Free Flight certainly would be disastrous. So a gradual and deliberate process of assembly and test of the Free Flight concept’s key elements has been the U.S. Federal Aviation Administration’s (FAA’s) modus operandi, under the agency’s mantra of "build a little, test a little."

Removing Restrictions

What exactly is Free Flight? The generally accepted definition, developed by a special RTCA committee of government and industry representatives in the late 1990s is:

…a safe and efficient flight operating capability under instrument flight rules [IFR], in which the operators have the freedom to select their path and speed in real time. Air traffic restrictions are only imposed to ensure separation, to preclude exceeding airport capacity, to prevent unauthorized flight through special use airspace [SUA], and to ensure safety of flight. Restrictions are limited in extent and duration to correct the identified problem. Any activity which removes restrictions represents a move toward Free Flight.

Having defined the goal, RTCA’s expert Free Flight Steering Committee then set about describing how the new concept could be made to work. Early in these deliberations the committee agreed that the basic infrastructure would require several essential elements to form the foundation on which the eventual final system would be built. Some elements, such as new computers and display equipment in the ATC centers, were already under way. Other elements, such as ground-based and airborne controller/pilot data link communications (CPDLC) equipment, were still at the conceptual stage. However, several key systems were already at, or close to, implementation readiness.

Status of Phase I

Five of these systems, called "enabling technologies," were selected to support the FAA’s Free Flight Phase I (FFP-1) evaluation initiative (see sidebar). These are:

  • Surface movement advisor,

  • User request evaluation tool,

  • Traffic management advisor,

  • Final approach spacing tool, and

  • Collaborative decision making, a completely new concept.

Notably, none of these elements requires aircraft operators to install any new equipment. This means that aircraft filing an instrument flight plan will not be excluded from the benefits the elements offered.

FAA Administrator Jane Garvey officially launched Free Flight Phase I in October 1998, stating: "Success with FFP-1 will show that we can do what we say we will do [and] that we can do what needs to be done–on time and within budget."

So far the project appears to be meeting those goals. However, in keeping with the "build a little, test a little" philosophy, the FAA did not plan to implement the five enabling technologies nationwide. Rather, the agency first would introduce the tools in areas having the highest traffic densities as core capability limited deployment (CCLD).

On to Phase II

FAA and industry officials are quite satisfied with the progress of FFP-1, which will continue until the end of 2002. In parallel with FFP-1, FAA launched FFP-2 in late 2000. Phase II builds on the experience gained and lessons learned from FFP-1 and will run until 2005. This phase involves wider geographic deployment of the five enabling technologies already operationally proven and adds refinements now being tested or in development. Phase II will introduce several new technologies, such as controller/pilot data link communications, which should relieve the extreme pressure on today’s VHF network and significantly reduce controller workload.

The FAA’s aim is to reach the calm and orderly traffic flow envisaged in the Boeing presentation of several years ago, but without recourse to miracles. However, Free Flight will not be achieved at the end of FFP-2 in 2005. FAA officials are cautious about forecasting exactly when that milestone will be reached, but unquestionably we should get very close to it by the end of the decade. As one FAA official put it, "One morning, we’ll wake up and realize that we’re there."

The FAA and Boeing

In June, FAA released its Operational Evolution Plan, a finely detailed description of all the myriad interlocking steps that must be taken over the next 10 years to produce a fully operational future environment capable of handling all sectors of aviation. A study of this plan, which is available upon request from the FAA, reveals the extraordinary amount of planning, coordination, system testing and subsequent procurement required to make our National Airspace System (NAS) work and keep on working in the face of the ever-increasing demands of the future. FAA critics would do well to study this document, to better appreciate just what it takes to produce and maintain one of the world’s leading air traffic management systems and to maintain that lead.

Coincidentally, Boeing chose the same day as the FAA to announce its vision of ATM. Like the FAA, Boeing’s aim is to increase airspace capacity and decrease delays, but the company made it clear that its new air traffic management unit, created last November, has a larger purpose–to ensure that the future skies do not become so crowded that airlines would start cutting back on their airplane orders. John Hayhurst, Boeing ATM’s president, emphasized this point by stating: "The future of our core business–building and selling jetliners–is tied to the future air traffic system, so we have a vested interest. We have a $30-billion business, which has limitations on growth because of the air traffic system."

Unfortunately, compared to FAA’s tightly defined and highly detailed program, Boeing’s approach was so generalized that one industry commentator–obviously a basketball fan–called the FAA plan a "swish" and the Boeing plan an "air ball." Boeing proposed to move the whole ATM system to a data link environment, where aircraft would fly trajectory paths in a voiceless sky and digital links would provide communications, navigation and surveillance via not-yet-built satellites from Boeing’s Hughes subsidiary. Boeing would dump FAA’s Local and Wide Area Augmentation Systems (LAAS and WAAS), which happen to be internationally standardized, and substitute signals from its new satellites. And Boeing would not proceed with Automatic Dependent Surveillance-Broadcast (ADS-B), even though U.S. and international ATC authorities regard it as a key future technology. Nevertheless, Boeing insisted that its concept–to which it would not attach a price tag but also would not fund–would, after an eight-year development period, successfully mesh with the FAA’s ongoing plan.

Boeing also would replace the FAA’s user request evaluation tool, often called "conflict probe," with a similar system that would predict an aircraft’s course by 40 to 50 minutes, instead of URET’s 20 minutes. Here, however, as in other areas, Boeing appears not to have consulted air traffic controllers who have told Avionics Magazine that there is little value in attempting to resolve possible conflicts more than 20 minutes ahead.

Some Missing Details

Unfortunately, too, Boeing spokesmen frequently turned away technical questions at the company’s briefing on the basis that these involved proprietary technologies that could not be discussed. Cost questions were similarly sidetracked. However, Boeing stressed several times that its ATM team recently had been bolstered by experts from its Joint Strike Fighter and its Space Shuttle programs, although exactly what relevant knowledge these people would bring to bear on civil air traffic control needs was not entirely clear.

On required avionics, Boeing would only say that modified, current-generation, airline flight management systems plus new 2 GHz data link units should be able to handle the company’s future concept. But a Boeing spokesman added paradoxically that general aviation could get by with a device similar to a "low-cost GPS."

Generally, industry observers have been skeptical of the Boeing proposal. Nevertheless, since its June announcement, Boeing has been actively promoting its concept to less sophisticated audiences on Capitol Hill and elsewhere. And some feel the manufacturing giant’s promised high-tech solutions, compared to the FAA’s cautious "build a little, test a little" approach, could win it many converts.

Five Enabling Technologies

The U.S. Federal Aviation Administration’s (FAA’s) Free Flight Phase I (FFP-1) initiative involves the test and evaluation of the following technologies:

The surface movement advisor (SMA) provides airline operations centers (AOCs) and airport ramp control personnel with continuously updated information on the identification and position of arriving and departing aircraft in the terminal area. Data on aircraft both in the air and on the ground is transmitted via a one-way feed from the local FAA surveillance radar. It is primarily intended to enhance airline gate and ramp operations, prevent runway gridlock and reduce taxi delays. Early airline tests at Detroit and Philadelphia airports demonstrated that SMA helped major air carriers avoid as many as five flight diversions per week. Since then, SMA has been installed at Atlanta, Chicago, Dallas/Fort Worth, Minneapolis, New York and St. Louis.

The user request evaluation tool (URET), commonly called the "conflict probe," continuously and automatically compares the filed flight plans of all aircraft and, using radar tracking updates and current winds data, determines whether potential losses of separation will occur. This is done up to 20 minutes of flying time ahead of a potential conflict–sufficient time for a controller to reach a resolution. The URET is installed at the Memphis and Indianapolis Air Route Traffic Control Centers (ARTCCs). En-route controllers also use the system to determine the acceptability of route or altitude requests, both in response to filed flight plans or to change requests as a flight proceeds. The URET will play a vital role in providing safe en-route traffic separation in the future Free Flight environment. Under FFP-1, URET installations are planned for Atlanta, Chicago, Cleveland, Kansas City and Washington, D.C.

The traffic management advisor (TMA) is a strategic planning tool for en-route controllers and flow control specialists. Installed at the Dallas/Fort Worth, Denver and Minneapolis Terminal Radar Approach Control (TRACON) facilities, the TMAs enhance arrival sequence planning by enabling controllers to develop otherwise complex arrival scheduling plans, or "meter lists," and runway assignments, to optimize airport capacity. Additional FFP-1 TMA installations are planned for the Southern California (Los Angeles), Atlanta, Miami, Oakland and Chicago TRACONS.

The final approach spacing tool (FAST) is one of few FAA acronyms that hints at what the system does. TMA hands over to FAST the control aircraft, which may be arriving from several different "corner posts," or entry points to the approach control area. FAST "feeds" the incoming aircraft to the approach controller in continuous, four-dimensional trajectories to a number of separate runways, e.g., the four in Dallas/Fort Worth. FAST directs the aircraft in a way that eventually brings them–sorted by type and in the correct in-trail spacing–over the threshold of their assigned runways. A prototype system, called pFAST, for "passive," has been in test at D/FW for three years and was declared operational in mid-1999. Testing has shown that capacity is increased and safety is enhanced, since controllers now can take a broader view of the approach scene. A second pFAST has been installed at the Southern California TRACON, as part of FFP-1. Other installations are under way at the Atlanta, Minneapolis, St. Louis and Chicago TRACONs. Later FAST versions will be called aFAST, for "active." They will give the controllers heading and speed cues.

The fifth element in Free Flight is not a piece of new technology, although it is a new ATC technique. Called collaborative decision making (CDM), it allows airline operations centers (AOCs) and FAA traffic specialists to discuss, cooperatively, the current status of the National Airspace System (NAS) regarding weather, schedules, equipment and delays. Introduced in the latter half of 1999, CDM already has shown its value when capacity limitations were expected and airline airspace rationing and schedule reductions were required. To succeed, of course, CDM demands a free and unrestricted interchange between airline personnel and FAA planners at the FAA’s Air Traffic Control Systems Command Center in Herndon, Va. As one FAA Free Flight official put it, "during these exchanges, there’s no holding back, and everyone has his cards face up on the table."

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