Free Flight describes a future air-traffic environment where we will fly unrestricted “trajectories” from departure to destination, based on our choice of route, altitude, speed, ETD and ETA, and with controllers sitting quietly at their screens while they monitor our progress to ensure we don’t get too close to each other.

Is this an impossible dream? Absolutely, many pilots flying in today’s system might justifiably answer. Yet we are slowly moving in that direction. In fact, as long ago as the mid-1980s some observers were already suggesting that aviation must move that way if we were to avoid the gridlock they felt would eventually overtake us.

By the early 1990s the threat of future gridlock had become sufficiently real to cause RTCA Inc., a not-for-profit, government/industry consultative organization, to establish a special task force on Free Flight, which it defined as “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.”

In 1995 the task force recommended a sequence of short-, medium- and long-term activities that would lead to that goal. Its report rejected “big bang” solutions, the most recent at the time being the FAA’s advanced automation system, which, when finally canceled in the early 1990s, was over budget by several billion dollars, with a seven-year delay in its promised delivery date. Instead, the task force proposed that each step along the way be evaluated against the FAA’s revised mantra of “build a little, test a lot.”

The task force stated that a number of key “enabling technologies” should be assembled before a realistic operational evaluation of the concept could begin. Some of these were already under way, like new computers and display equipment in the ATC centers, while others–like ground-based and airborne controller/pilot datalink equipment– were still in the early development stages.

However, four new elements were already at, or close to, readiness and were selected to support the first evaluation, called Free Flight Phase I (FFP-1), which was launched in October 1998. These four technologies were the surface movement advisor (SMA); user request evaluation tool (URET); traffic management advisor (TMA); and final approach spacing tool (FAST).

To these was added a completely new concept called collaborative decision making (CDM). Other than CDM, none of the Free Flight enabling technologies were to be implemented nationwide, but would be introduced in different, occasionally overlapping, high-density areas. Importantly, none would require operators to install new equipment, which meant that all aircraft flying on IFR flight plans in their coverage areas would benefit.

Additionally, since the first four systems provided controllers with data that supplemented their normal information sources, pilots would never fly in an evaluation-only environment. Finally, the FFP-1 evaluation was to run from October 1998 to December 2002, and would be subject to continuing benefit assessments, overseen by a Free Flight Select Committee, composed of government and industry representatives, including NBAA.

Technology Explained
The surface movement advisor provides continuously updated information on the position of arriving and departing aircraft in the terminal area, both in the air and on the ground. SMA is primarily intended to enhance airline gate and ramp operations, prevent runway gridlock and reduce taxi delays, and has been installed at Detroit, Philadelphia, Atlanta, Dallas/Fort Worth, Chicago and New York. The FAA reports that during inclement weather, SMA has helped avoid as many as five airline diversions per week.

The user request evaluation tool– sometimes called the conflict probe–uses radar tracking and current winds to continuously and automatically monitor the flight paths of all aircraft to determine whether potential losses of separation will occur, as far as 20 min of flying time ahead, and alerts controllers whenever such risks appear. Controllers also use the system to determine the acceptability of route or altitude changes, in response to aircraft en route requests.

URET will play a vital role in providing safe traffic separation in the future Free Flight era. Currently installed at Memphis and Indianapolis, FFP-1 URET installations are planned for Kansas City, Washington, Cleveland, Atlanta and Chicago. Estimated operator savings are already stated to be almost $2 million dollars per month.

The traffic management advisor was developed by NASA as a strategic-planning tool for Tracon controllers and terminal area-flow control specialists, who use it to develop complex “meter list” arrival schedules and runway assignments to optimize capacity at major airports. TMA is currently installed at Dallas/Fort Worth, Atlanta, Denver and Minneapolis, with additional installations planned for Los Angeles, Miami, Oakland and Chicago. Data from Dallas/Fort Worth indicates a 5-percent increase in acceptance rates, and daily delay reductions of nine hours.

The final approach spacing tool is another NASA development, which works in conjunction with TMA. FAST progressively accepts aircraft from the TMA and “feeds” them–in continuous, 4-D trajectories, sorted by type and in the correct in-trail spacing–to the thresholds of their assigned runways, thereby greatly relieving the pressure on controllers.

The initial FAST installation at Dallas/Fort Worth has been followed by a second installation serving Los Angeles, with others under way at Atlanta, Minneapolis, St. Louis and Chicago. FAST has produced a 5-percent increase in peak operations, while providing controllers with a much broader monitoring view of the total approach scene.

The fifth element, CDM, is not solely a piece of new technology, but is a combination of new ATC tools and procedures. CDM allows system users (primarily the airlines) and FAA traffic specialists at the agency’s Herndon, Va., ATC System Command Center and at affected ARTCCs to cooperatively plan bad-weather strategies when capacity limitations are expected, requiring airspace rationing and schedule reductions.

Every two hours, from early morning until late evening daily, a telephone conference line is opened up and all participants review the current situation across the National Airspace System (NAS) and assess action plans for the next four to six hours. This is the unique aspect of CDM, in that it demands a completely free interchange of data between system users and FAA planners. An FAA official observed, “During these exchanges, everyone has their cards face up on the table.”

Yet even before the command center conference line opens up, user weather specialists and National Weather Service experts at the Aviation Weather Center in Kansas City will, very early in the morning, have completed their Internet exchanges and produced their nationwide collaborative convection forecast product (CCFP) to guide the day’s activities.

Where does corporate aviation fit into this? As said earlier, NBAA has been an active member of the Free Flight Select Committee, where it is represented by Bob Lamond Jr., manager of air traffic services and infrastructure. Lamond told AIN that NBAA is very supportive of Free Flight: “It is critical for adding efficiency and capacity to the NAS.”

Asked whether the concept’s benefits weren’t mostly supporting the airlines, he pointed out that Free Flight benefits all airspace users. “All ships rise with the tide,” he said, adding that in the en route, terminal and approach segments under URET, TMA and FAST, Free Flight Phase 1 doesn’t discriminate between aircraft. “If you are on an IFR plan, you will get the same handling as everyone else.”

What about participation in the CDM discussions? “That’s coming,” said Lamond. To date, NBAA has been primarily involved in the strategic planning of CDM techniques, tools and procedures. But now, he said, NBAA has been welcomed by CDM participants to enter the tactical daily activities, and it is currently developing methods to accomplish this.

One problem, he pointed out, is that over half the association’s approximately 4,400 member companies operate just one airplane, making individual participation in the command center’s conference calls impractical. One solution could be to have flight-planning service provider companies monitor the calls and feed data back to their clients.

“On the other hand,” said Lamond, “the remainder of our member companies operate variably sized fleets in ways very similar to the smaller airlines.” He mentioned that NBAA was reviewing marketing schemes and subscriber fees for CDM participation, which were expected to be announced shortly and discussed at this month’s NBAA show in New Orleans.

FAA and industry officials are extremely satisfied with the progress of FFP-1, and the project appears to be both on time and within budget. Late last year, the FAA launched FFP-2, which will build on the lessons learned from FFP-1 and will run until 2005. FFP-2 will expand coverage of the four systems now operationally proven, but with added refinements. It will also introduce several new technologies, including controller/pilot datalink communications, which will relieve the extreme pressure on today’s VHF network, and significantly reduce pilot and controller workload.

Nevertheless, full Free Flight will still not be achieved when FFP-2 ends in 2005, since many more future developments are foreseen. Consequently, FAA officials are cautious about forecasting exactly when the final, complete state will be reached, but expect to be getting close to it by the end of the decade. As one official put it, “One morning we’ll wake up and realize that we’re there.”