A Simulating Experience

A pilot radios the tower at Chicago’s O’Hare International airport, “Tower, Eagle Flight 559 is outside the outer marker, two-eight center.” The controller, without missing a beat, responds “Eagle 559, O’Hare, you’re number two; you’re following traffic still two out; runway two-eight center, cleared to land.” Wait a minute – O’Hare doesn’t have a runway two-eight center. Yet, this exchange did take place — at FutureFlight Central’s air traffic control facility at the NASA Ames Research Center in Mountain View, CA. It’s a telling tale.

Over a six-week period in August and September 2005, controllers from O’Hare fast-forwarded to the year 2018, operating a real-time, human-in-the-loop (HITL) simulation of a new airport layout plan (ALP) defined by the O’Hare Modernization Program (OMP).

The OMP is a multi-billion dollar program by the City of Chicago to reduce delays and congestion at one of the world’s busiest, and most-delayed, airports. It will reconfigure O’Hare’s intersecting runways into a more modern, parallel layout that will substantially reduce delays in poor weather conditions and increase capacity at the airfield. Phase I construction is underway, and the full build-out is scheduled to be completed by 2013.

The key feature of the new ALP is the addition of one new runway, and the realignment of three existing runways to establish a system of parallel runways that ensures at least three arrival and three departure runways are active even in poor weather conditions. The peak operational capacity of the new ALP, under visual conditions, is expected to reach 300 operations per hour. In addition to the new runway layout, the OMP includes a new western terminal complex with 60 gates, and extensions to the K, L, and M (international) concourses that will add some 20 new gates.

Bringing ORD to FutureFlight

FutureFlight Central (FFC) is one of a suite of air traffic control (ATC) and cockpit simulators that comprise the “SimLabs,” or Simulation Laboratories, at NASA Ames. A virtual ATC tower, FFC is a national Air Traffic Control/Air Traffic Management (ATC/ATM) test facility dedicated to solving safety and capacity issues at the nation’s busiest airports. The two-story facility offers a complete tower operating environment including a 360-degree full-scale 3D out-the-window view of an airport. Controllers, pilots, and airport personnel participate in real-time simulations to optimize expansion plans and operating procedures, and evaluate new technologies.This is all done in the safety of a simulated environment without any impact to the users. The facility is a realistic environment that enables stakeholders to achieve consensus through a common vision of the future.

FFC provides detailed and realistic 3-D airport database models displayed on twelve projection screens to provide the 360-degree out-the-window view. Interactive tower displays support all air and ground positions controlling traffic within the terminal air space. Up to 12 controller positions, four ramp tower positions, and 16 sim-pilot positions are networked in real-time.

A digital voice communication system allows controllers to talk to pilots and coordinate in the tower, as they would in real life.

The data-collection capabilities in FFC include a wide array of surface performance measurements for aircraft and ground vehicles, controller and pilot communication metrics, and audio/video observational and debrief data. This high-fidelity collection of human-performance data, and airport surface data that includes human-performance factors, provides stakeholders with information that can be used to fine-tune airport designs and operations, and to develop, modify, and validate procedures in the tower.

Real-Time Simulation Defined

Real-time simulation immerses human participants in the operating environment. By including human factors in the analysis of a “future airport,” extremely valuable information can be gathered that is not obtainable through other methods. As a step in the design process, real-time simulation provides huge potential cost benefits and efficiency improvements ­— all without the turn of a shovel.

The OMP initially considered 15 alternatives, ranging from non-airfield development to several proposed airfield configurations.

In evaluating the relative benefits of the three alternatives that survived the initial and secondary screening processes, the City of Chicago and the FAA conducted an unprecedented series of fast-time simulation analyses. The studies provided a basis for the assessment of the operational performance of the three alternatives. One alternative performed best from a “delay and travel time” perspective.

The O’Hare tower’s Air Traffic Working Group developed an operational concept delegating workload to different controllers throughout the tower cab under the proposed ALP. While confident of the concept, validation of workload levels and coordination between controllers was needed to eliminate concerns. Could the expected traffic levels be managed in the real-life environment? What issues or solutions might exist that could not be envisioned using computational methods?

Human-centered objective and subjective data collected in FutureFlight Central provide accurate workload measures that cannot be obtained in a fast-time simulation. In addition, participants can provide valuable feedback based on their observations and experiences from the simulation.

OMP’s Unanswered Questions

The simulation at FFC was designed specifically to answer those human-factors and procedural questions that fast-time methods are not equipped to address. By providing an environment in which the O’Hare controllers could experience the future ALP, they were able to address many important questions, including:

  • How many controllers are required to manage the traffic?
  • How should the movement area and traffic be divided up among the ground controllers?
  • How manageable was the workload at the ground controller positions?
  • What was the impact of the new ALP on the local controller workload?

From the fast-time analysis of the new ALP, it was known that there would be traffic “chokepoints” for both the East- and West-flow cases — that is, intersections on the airfield where multiple streams of traffic came together and, if not properly managed, could lead to gridlock.

How manageable would these chokepoints be, at peak traffic levels, with pilot/controller communications, controller coordination demands, and human factors such as reaction time and “working speed” all affecting the controllers’ ability to move traffic? Could mitigation strategies be developed for these chokepoints, given the taxiway layout defined by the ALP? Were there taxiway modifications that would enhance the operational efficiency of the airport?

And, there were other questions: How effective would standard, or “coded” taxi routes be for the new ALP, and what would be the impact of traffic management initiatives on airport efficiency and controller workload?

The FAA is planning to build a 22-inch high platform in the center of the O’Hare tower for the ground controllers. This elevated, more centralized view will enhance the controllers’ ability to maintain visual contact with their traffic. During the simulation at FFC, a mockup of the platform was built and installed in the tower cab. This allowed controllers to evaluate the effectiveness of the configuration as part of the simulation, before any work began in the tower at O’Hare.

Gearing Up for the Simulation

The OMP real-time simulation represented the largest simulation of its kind ever attempted. A staff of 25 individuals was hired to act as “sim-pilots” for the simulation, and were trained over a period of six weeks to communicate with the controllers and operate the traffic at the “new” O’Hare. The job of the sim-pilots is complex and demanding for busy airports like O’Hare. The success of the simulation is dependent upon the sim-pilots’ ability to work together as a group to manage the high levels of traffic around the airfield, which provides the O’Hare controllers with the look and feel of really “being there.”

Nine controllers from the O’Hare tower participated in the simulation. Since this was a substantially new airport, they underwent their own training to prepare for the simulation. A two-day class was conducted at O’Hare in May 2005 in which the controllers were briefed on the new airport layout, runway and taxiway names, and the proposed traffic flows. In addition, each of the controllers spent at least five days at FFC, controlling traffic during sim-pilot training.

The simulation itself was conducted over a five-day period in September 2005. There were four runs per day, each lasting 45 minutes. Controllers were exposed to East and West traffic flows, in both visual and instrument conditions, with traffic levels that approached 300 operations per hour. Some runs introduced traffic management initiatives to create more complicated — and more realistic — traffic situations. In addition, gate-holds for occupied gates were required; go-arounds were issued when appropriate; and one run simulated an aircraft breakdown on arrival; and the subsequent runway closure. All of these factors provided the controllers with a very real sense of how the airport will operate when it’s completed.

The controllers staffed the FFC tower for each simulation run as follows: a total of six local/ground controller positions, one outbound ground-metering position, one inbound-metering position, who managed the arrival flight strips, and one traffic manager. Controllers changed positions for each run to expose them to all of the positions in the tower.

Data Collected

The main focus of the data-collection effort was on data not readily available from the fast-time analysis. Digital audio recordings of pilot/controller communications were generated for each run, and processed to provide statistics such as number of transmissions per hour, and average length of transmission. These data are useful for workload analysis and are a factor in the safe operation of the airport. During each run, activity in the control tower was recorded on video to document such factors as controller coordination, and the physical workload of each position — how much moving around in the tower was required, and the scope of their respective viewing ranges.

At the end of each run, the controllers filled out surveys. The surveys asked controllers to rate various factors for the new ALP relative to their current experience at O’Hare, including traffic complexity, aircraft ownership recognition, tower coordination, and radio communication. Also, debrief sessions were conducted after each run in which the controllers provided feedback from the run.

This feedback ranged from the positives and negatives for the run, to what changes could be made to improve their ability to move the aircraft. These suggestions included ideas on how to better balance the workload in the tower and move the aircraft more efficiently, and how the airport layout might be altered to address particular problems encountered in the traffic flow on the airport surface. Some of these ideas were implemented in subsequent simulation runs to test their effectiveness.

What WAS Learned

“NASA’s facility helped us determine how our air traffic operation can work at peak efficiency within the tower at the future O’Hare,” according to Suzan Jardine, Project Lead for Central Terminal Operations in the Chicago Area Modernization Program Office. “The simulation offered a unique opportunity to study how FAA air traffic controllers can best communicate with each other and interface with the tower’s new technology and new demands. As O’Hare Airport modernizes, the FAA will be able to hit the ground running and keep the air traffic operation performing smoothly.”

The O’Hare simulation provided a unique opportunity for stakeholders to experience the proposed ALP. During their time in FFC, the controllers were able to make significant improvements in several areas, including workload balancing and chokepoint mitigation. There were also suggestions regarding the airport layout that might improve the efficiency of the operation. The findings from the simulation provided the OMP office a basis to open a dialog regarding future modifications to the ALP that would enhance overall operations.

Controllers were able to experience first hand the benefits of the new ALP in poor weather conditions. The parallel runway structure greatly simplified poor-weather operations, while maintaining six active runways for maximum throughput. They identified potential issues with maintaining optimal departure sequences, due to limited taxiway or hold-pad availability to re-sequence departures, as changing traffic management initiatives might dictate.

Operational changes were made in the tower that significantly improved the ability of the controllers to manage the workload for the new ALP. Areas of responsibility were redefined to better balance the workload between the two inbound ground controllers. The positions transitioned from what was originally envisioned as an East/West split of responsibilities, to a more North/South split. A repositioning of the ground controller positions on the center platform was performed to support the changes. The workload for two of the local-controller positions was made more manageable by offloading some of the taxiing arrival traffic onto the inbound ground controllers.

Significant improvements to the chokepoint issues were developed during the simulation. The use of underutilized taxiways, coupled with the redefinition of the inbound ground controller responsibilities, created a more efficient operation, even during peak-demand operations. For the West-flow operation, there is still some concern with a particular chokepoint, and the overall taxi length to some of the gates for arrivals on the North-side runways. A proposed solution to this issue was developed, and is currently under consideration.

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By the end of their time in FFC, the participating ORD controllers had a good feel for operating the new O’Hare ALP. They began the project knowing little about the new ALP, but by the conclusion of the simulation were able to operate it effectively and efficiently. Any changes implemented now based on their observation and feedback during the simulation will reduce the risk of discovering needed changes late in the project. In addition to saving on the overall cost of the project, the simulation results will help ensure that the final build-out of the new ALP will be an efficient operation both on the airfield and in the tower, and that there will be few, if any, “surprises.”