Decision Aid for Controllers Helps Prevent Near-Misses

August 2014
Topics: Air Traffic Management
MITRE has developed a tool to mitigate the hazard that unanticipated go-arounds present to departing aircraft. It's been called a "significant procedural improvement" for air traffic control.
Plane taking off.

A MITRE-developed decision aid for air traffic controllers is helping prevent a rare but dangerous occurrence at some of the nation's airports—a missed approach, or go-around, that causes an arriving aircraft to come too close to a departing aircraft.

Near mid-air collisions, defined as aircraft coming closer than 500 feet to one another, are among the most serious safety incidents in aviation. Their prevention is of the highest priority for the Federal Aviation Administration. Although rare these events occasionally occur when arriving aircraft must execute a missed approach while another aircraft is departing along a converging path. However, discontinuing the use of these intersecting or converging operations would result in a major reduction in capacity at many of the nation's busiest airports. Therefore the FAA asked MITRE to develop a capability for near-term implementation that would mitigate these risks. FAA officials have praised our resulting work as noteworthy.

The Arrival-Departure Window: An Effective Safety Tool

Missed approaches occur in only about one in 1,000 flights and are difficult to predict. It is also difficult for an air traffic controller to estimate a release time for a departure aircraft that will ensure the departure is safely separated from an arriving aircraft executing a last-minute, missed-approach maneuver.

One mitigation is for the controller to use an arrival-departure window (ADW). An ADW is a pre-defined region along the approach path that must be free of arriving aircraft before air traffic controllers can release a departure. This window ensures that arriving and departing aircraft remain at a safe distance from one another, even if the arriving aircraft must discontinue its landing.

Because of the known effectiveness of such windows—and many facilities' preference for them over other mitigations—MITRE began developing arrival-departure windows for the nation's busiest airports in 2013.

Using Modeling and Simulation to Create the Windows

Development of the ADWs built on a previous effort: the development of MITRE's Intersecting Operations model. This simulation tool helps assess airborne collision risk for runways with intersecting or converging operations and quickly generates arrival-departure windows to address those risks.

"The model runs the fast-time simulation millions of times for each intersecting or converging scenario to evaluate the risk with flights of different speeds, trajectories, and other factors," explains project leader Michael Henry. "That gives us the information we need to size the distance from the approach end of the runway that's required to create an arrival-departure window. That space is also known as a 'no go box' or a 'no fly zone.'" The FAA then adds these windows to the controllers' displays so they can quickly and easily determine when, during an arrival's approach, it's safe to release a departure.

Rapid Implementation Supports Safety and Efficiency

As of June 2014, arrival-departure windows had been delivered to the 17 largest airports with converging runway operations. In addition, MITRE has transitioned the tools and capabilities necessary to create arrival-departure windows to the FAA's Air Traffic Organization. The improvements will include real-time calculations based on the actual characteristics of the arriving and departing aircraft and development of an arrival-departure window that would automatically change in response to these calculations.

"Controllers at many of the nation's busiest airports now have one or more arrival-departure windows—developed using MITRE's model—that will aid them in safely using the capacity of intersecting runway operations," notes Glenn Roberts, chief engineer of MITRE's Center for Advanced Aviation System Development, the federally funded research and development center serving the FAA.

"The development of this quantitative model to establish arrival-departure windows allows controllers to augment their operational skills, ensures maximum safe efficiency of both runways, and potentially saves lives," adds Joseph Teixeira, vice president for Safety and Technical Training in the FAA's Air Traffic Organization, which sponsored this work. "This tool is the most significant procedural improvement we have made in air traffic control in the last decade."

—by Marlis McCollum

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