A Californian simulation centre is taking the guesswork out of the complicated and expensive process of expanding airport capacity

As returning air traffic begins to tax runway capacity again, airport operators are looking at more efficient and safer ways to manage aircraft movements on the ground. Changes to runways and taxiways have a domino effect, often extending into the en route air traffic control domain. As a result, any airport capacity enhancement must consider the human factor before concrete is even poured.

Putting the human into the airport improvement planning loop is the mission of FutureFlight Central (FFC), a jointly funded NASA-US Federal Aviation Administration facility designed to simulate the total airport terminal environment. NASA says FFC is the only "live action" simulation supporting all interacting functions - approach control, tower, ramp and pilots. FFC's customers have included San Francisco, Dallas/Fort Worth, and Los Angeles International airports.

Housed in a two-level building at Ames Research Center in Moffett Field, California, FFC's ground floor includes a briefing room and space for airport operators and test engineers. Up to eight ramp controllers and 13 "pseudo-pilots", who communicate with the tower controllers during simulated airport traffic control scenarios, are also located on the ground floor. The tower controllers, who are the primary scenario participants, work in the tower cab, which occupies most of the second floor, with a 360¡ visual system which can display any airport surface and terminal airspace entered into FFC's database.

Digital simulation

Building a database takes about three months, and requires digital imagery to be shot at 15-20¡ intervals at the airport to be simulated. This is combined with digital terrain-elevation data, airport design files, and high-resolution aerial and close-up photography. The database supports views of the airport from any location, allowing simulation and playback to show views from the ATC tower, ramp tower, as well as perspectives of pilots and ground-vehicle operators.

FFC uses ATC simulation software from Adacel, and six Silicon Graphics computers running Multigen image-generation software. The image generators produce a photo-realistic out-the-window view under visibility conditions including fog, day and night. Included are all buildings around the airport, highly textured paved and unpaved surfaces, as well as moving vehicles and aircraft. The library includes 60 different civil, military and general aviation aircraft models, each with five to 10 different liveries that are kept current. As many as 100 simulated models - aircraft and vehicles - can be displayed.

Controllers view the simulated scene through 12 floor-to-ceiling windows, each located in front of a rear-projection display screen. "We installed the windows because they give the controllers the same acoustical feel they would have if they were standing next to a window in a real control tower," says Ken Christensen, FFC business development manager.

The tower cab has positions for up to 12 controllers. Up to six interactive radar displays can be suspended from a ceiling track. Each controller station - as well as those for ramp operators and pseudo-pilots - has a touch-screen communication interface along with combination headset/ microphone and a pull-out keyboard for the input of specific aircraft flight data.

Scenarios run within FFC's fully immersive environment are designed to aid the evaluation of any proposed airport runway, tower, or taxiway changes from the controller's perspective. "For example, if an airport operator wants to move the control tower, or put in new taxiways, the best sites to assure maximum controller efficiency must be determined," says Christensen. "After the location of the tower or taxiways is simulated, the controllers can get an accurate picture of how the airplanes and ground vehicles will move about the airport, and see the impact of the proposed changes. This allows the airport authority to arrive at the best solution before any construction takes place."

While FFC uses a cadre of specially trained pseudo pilots working from computer workstations, scenarios can also be run using pilots in full-flight simulators. These include the Crew Vehicle Systems Research Facility (CVSRF) in an adjacent building at Ames. This houses two FlightSafety-built aircraft simulators - a Boeing 747-400 and the Advanced Concepts Flight Simulator, which can simulate any aircraft, and any aircraft control laws.

Also available is the vertical motion simulator (VMS) in another building at Ames. This can accommodate interchangeable cabs for any fixed- or rotary-wing aircraft. "The centre's capability to network with full-flight simulators allows pilots to fly a simulated approach or departure - in any aircraft type - to any proposed new or reconfigured runway, and use any current or future taxiway design. This gives us feedback from pilots as to how comfortable they are, and provides input on any changes to the design that could be made," says Christensen.

Taxiway projects

Two airport authorities are moving ahead with major new taxiway projects based on validation by FFC. Los Angeles International (LAX), which plans to construct a new taxiway to mitigate a problem with runway incursions, began working with FFC in early 2001, says airfield operations chief Raymond Jack.

"Our concern was how to study the problem without impacting the daily operation of the airport, itself," he says. "We concluded that our best alternative was FutureFlight Central, which offered two things nobody else did - high-fidelity simulation, and the ability to put a human in the loop. This was important because we could station some of our own controllers in the tower and see their reaction to the various scenarios we would run."

The focus of the incursion study was on the two parallel east/west runways - 25L and 25R - on the airport's south side. "In 2001, we had a local controller who was responsible for managing the south side, and one for the two east/west runways on the north side. We wanted to see if having an additional controller to manage the south airfield might make a difference," says Jack. After running seven scenarios at FFC over five days, it was determined the additional controller would add to the present south-side controller's workload, and the idea was abandoned. But other possible solutions were explored at the same time.

"At LAX, all departing aircraft normally use the inboard [to the terminal] runways with the arriving aircraft assigned to the outboard runways," says Jack. "We ran scenarios that switched this procedure. But the problem was that the departing aircraft would have to cross an active arrivals runway, and we found that, once again, controller workload increased."

Another alternative was to build a "bypass" taxiway that would allow arriving aircraft to exit runway 25L and go around the terminal without intersecting runway 25R. It was found this would conflict with instrument procedures for departing aircraft.

LAX representatives returned to FFC in June 2003 to look at yet another proposed solution to the incursion problem. This involved construction of a new taxiway parallel to - and between - runways 25L and 25R. Twelve scenarios were run over three days, simulating pre-11 September traffic levels and involving four LAX controllers. "We found that this was workable from a controller standpoint, and could significantly reduce runway incursions," Jack says. The simulation also indicated that, to accommodate the new taxiway, runway 25L would have to be moved about 17m south, which could be done without affecting structures on the south side.

"The simulation also showed us that runway occupancy time for the arriving aircraft would stay about the same. Along with this, Los Angeles TRACON would be able to keep the same in-trail distances between landing airplanes," says Jack. The new taxiway is being fast-tracked under the LAX Master Plan, which is ready for submission to the Los Angeles City Council.

Dallas/Fort Worth International commissioned FFC to study human factors involved in a proposed perimeter taxiway to reduce significant incursion risks where taxiways crossed the five north/south parallel runways and diagonal northwest/southwest runways on each side of the airport, says executive vice-president operations Jim Crites.

"We had to be able to put the human in the loop as an integral part of the perimeter taxiway demonstration," says Crites. During the demonstration in February 2003, 13 scenarios were run over four days. It was shown the perimeter taxiway would eliminate all runway crossings. Participants included five DFW controllers and seven airline pilots. "We gave them the ultimate call as to whether this [taxiway] would be a good idea," says Crites.

"By using FFC we learned that aircraft throughput would be improved by 30% if the taxiway were built," he says. "We found the controllers were able to focus better on what they were doing by concentrating the workload where it needed to be. That reduced stress levels among the controllers, and confirmed the taxiway would be a tool to avoid runway incursions."

The perimeter taxiway is going through the FAA approval process. If approved, construction should begin by 2006, with completion of the east-side first phase by 2008 and the west-side second phase by 2010.

FFC is open to international airport operators, says Christiansen, although its only clients so far have been US. "We are in talks with a few US airport authorities that are going through revisions to their master planning process," he says.

Source: Flight International