ARIAS: A Near-Term Runway Safety SolutionNovember 2011
Topics: Air Traffic Management, Airports
On February 1, 1991, a USAir 737 was making its final approach to Los Angeles International Airport. On the runway below, SkyWest Flight 5569, a twin-engine turboprop, waited to take off. A series of errors and misjudgments had led air traffic control to assign the same runway for both the 737's landing and the turboprop's departure. The pilot of the 737 did not see Flight 5569 in his path until his wheels settled onto the tarmac. By then it was too late. The jet crashed into the turboprop, crushing the smaller plane beneath it. All 12 passengers and crew aboard Flight 5569 and 22 of 89 people on Flight 737 died in the collision.
Since this disaster, innovations in airport safety—better communication systems, improved ground radar, enhanced situational awareness tools—have been introduced to address such problems. But runway incursions—which occur when aircraft, vehicles, or people mistakenly end up in areas designated for the landing or take off of aircraft—still happen too often. U.S. airports reported almost 1,400 runway incursions from 2001 to 2004. (Fortunately, most incursions do not result in accidents.) The National Transportation Safety Board consistently mentions runway incursions in its list of the "10 most wanted" transportation safety improvements.
In partnership with the Federal Aviation Administration and in concert and collaboration with many other organizations, MITRE has been developing new concepts, collectively called the Next Generation Air Transportation System, to improve the U.S. national airspace system. NextGen concepts and associated technologies will advance air traffic efficiency and safety, including limiting runway incursions. But the task of implementing NextGen will continue for many years to come. In the meantime, the aviation community needs short-term, easy-to-implement solutions for keeping runway operations safe.
Four years ago, MITRE engineers Dave Domino, Peter Moertl, Jim Nickum, and Doyle Peed began bandying about ideas for such a solution. They held a series of informal brainstorming sessions from which arose the Arrival Runway Incursion Alerting System (ARIAS). Using equipment already installed in most aircraft, ARIAS would provide an auditory warning to the pilot of any aircraft flying an approach to a runway on which another aircraft poses a collision risk.
Time = Safety
This simple solution required a lot of rumination over a complex problem. Most busy airports monitor runways using ground radar surveillance systems. When the surveillance system detects a potential aircraft conflict, it notifies air traffic control. The controller then needs to consult his system display, determine which two airplanes are involved, determine a course of action to avoid the conflict, and, finally, communicate that course of action to the flight crews.
"While this system has been useful," says Domino, "one acknowledged deficiency is the inherent delay between the time when the conflict is detected and the time when the pilot can take corrective action. As long as you're relying on the controller to relay the conflict alert, even with perfect performance that time delay will remain a problem."
To cover that deficiency, the National Transportation Safety Board has recommended that the FAA develop a system that, once an airport's surface surveillance system detects a potential conflict, communicates a conflict alert directly to the incoming airplane. This would provide a pilot with more time to react. The four MITRE engineers realized that the quickest development route for such a system would be to identify equipment already present on airplanes that could be repurposed to deliver an alert to the pilot. Their thoughts soon focused on the marker beacon system.
At the Sound of the Tone
The marker beacon system helps guide pilots making instrument landing approaches. The beacons are installed at set distances from the airport and transmit auditory signals that inform the flight crews that their aircraft is flying overhead of the beacon position, as depicted on the approach chart, relative to the runway. Every aircraft designed to make instrument landing approaches is equipped with a marker beacon radio receiver.
"So we thought, since the pilot is already monitoring the marker beacon system, why not use it also to deliver an auditory alert of a runway conflict?" asks Domino. "The technical challenge was to design a system where the marker beacon and conflict-alert functions would not interfere with each other."
Peed explained how ARIAS works. "What we're doing is taking the marker beacon carrier frequency and modulating it to provide a runway-conflict audio alert. By offsetting the carrier just a little bit, the conflict alert can still be picked up by the plane's receiver without interfering with the marker beacon signal."
Piggybacking on the marker beacon system not only takes advantage of equipment already installed on the aircraft, Moertl says, but also takes advantage of the simplicity of the system's auditory signal. "ARIAS is not reliant on a visual signal. There is no need to install signal lighting along airport runways. The low-visibility conditions that often cause runway incursions would not affect the alert system."
"And with all the visual information a pilot has to process during a landing, such as observing conditions and monitoring his instruments," Domino adds, "we wanted to avoid adding to the pilot's visual load. We wanted to keep the alert system simple."
The ARIAS designers are in fact worried that ARIAS's simplicity might cause the aviation community to overlook it in the effort to prevent runway incursions. While they are confident that the NextGen technologies MITRE is helping develop—systems like Automatic Dependent Surveillance-Broadcast (ADS-B), which uses GPS to determine a plane's exact location—will eventually provide a long-term solution to runway safety, they see ARIAS as an elegant stopgap solution. "Commercial aircraft are not required to have the necessary ADS-B avionics until 2020 at the earliest," points out Peed. "ARIAS could be implemented almost immediately."
Earlier this year, the U.S. Patent and Trademark Office awarded Domino, Moertl, Nickum, and Peed a patent for "Methods, Systems and Computer Program Products for Communicating Auditory Alerts to Aircrafts." Now the designers are ready to put ARIAS through its paces.
"The next step," says Moertl," is to go through the prototyping and testing stages to demonstrate ARIAS's capabilities." If ARIAS lives up to its designers' expectations, pilots could soon be flying their approaches to worry-free runways.
—by Christopher Lockheardt