ATM Modernization

Raytheon Adding Automated Approach Verification to Airports in the NAS

By Nick Zazulia | October 25, 2018
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Raytheon STARS

A controller sitting at a next-generation Raytheon ATC station. (Raytheon)

Raytheon is leveraging its air traffic control technology, the standard terminal automation replacement system (STARS), to prevent situations like last year's Air Canada Flight 759 near-miss at San Francisco International Airport (SFO) that almost became one of the worst aviation disasters in history.

STARS is in place at just about every airport — and almost every military airfield — in the U.S. and many abroad, some 650 total, and it aids controllers in managing all departures and arrivals in the national airspace system (NAS). According to Raytheon's STARS program manager, Chris Rogers, that kind of infrastructure provides an opportunity to solve problems outside of the system's original requirements.

"Could we make a change that could be used by every facility without making a change to hardware?" Rogers said Raytheon asked in the wake of AC759.

The answer turned out to be yes, which the company is doing with the approach runway verification (ARV) software upgrade it is adding to its STARS system.

The investigation into the Air Canada incident at SFO found that the incoming flight was lined up with the incorrect one of two parallel runways. Neither the pilots nor the controller on duty realized it, and there is no system in place to automatically alert to something so minor being amiss. In that case, the incorrect runway was being used as a taxiway, and the arriving flight came within feet of landing on top of other planes on the runway before executing a go-around to align with the correct runway.

In its recently released investigation report, the NTSB called for the FAA to have industry develop and then implement a solution that would automatically detect when planes are misaligned. That's what Raytheon has been doing, and the FAA has approved it to go forward with a prototype.

Rogers said that the near-miss in San Francisco wasn't an isolated incident. He said that "up to two times a day" throughout the NAS, planes align with incorrect runways. Because misses don't involve actual collisions, he said controllers often choose not to report them — even in the case of the almost-catastrophic AC759, it wasn't reported immediately.

"So until there's an incident, how do you know it's an issue? How do you justify the investment to go incorporate something until you know how often it happens?" Rogers said.

As controllers have had easy access to systems on handheld devices, though, they have been encouraged more to submit potential incidents, which has led to "more realization about these things happening" over the past few years. Additionally, the surrounding requirements prime the NAS for the ARV capability.

In essence, ARV is a new way of reading and using the data that STARS fuses from the sensors it takes in, passing it through different filters and setting appropriate alerts. The controller sets an incoming flight in the system to be cleared for a certain runway, and the system correlates its knowledge of where that runway is with data from different sources and compares that with historical data about trajectories and positions for incoming flights.

"The software knows whereabouts the plane should be at a certain point in the route," Rogers said. "If it's outside these parameters, it creates an alert. It uses the same sensor feeds that the terminal controller uses for the sequencing and spacing of aircraft."

When a final monitor aid alert pops up for the controller to check on a flight, they can direct the pilot to re-align with the correct runway or initiate a go-around.

One of the keys to the system is ADS-B position-reporting, so the proliferation and pending regulatory requirement for that technology help enable ARV's effectiveness throughout the NAS. That's particularly important since, according to Rogers, a lot of the issues that ARV could solve occur at general aviation airports. Naturally, those smaller airports tend to have a less robust set of sensors, but as long as they have ADS-B and something to pair with it, Rogers said Raytheon is confident the system would still slot in without issue.

The STARS update with ARV should be ready for the FAA in the third quarter of 2019. Rogers said he anticipates that, after the FAA does all of its testing, nationwide rollout of the software will commence in 2020.

There will be some additional training required for controllers to use the new system — for it to work, they need to input a runway for each incoming flight, though if they fail to do so, STARS will treat it like a misalignment and provide an alert. There will also be some customization needed for certain locations.

"No two [airports] have the same setups; there are different approach paths, crossing runways, curved runways, straight on, et cetera," Rogers said. "The river approach at Potomac [Airfield], we looked at Boston and New York ... It's just some adaptation, they have to align when they want the alerts and things, which is typical for STARS."


The air traffic control tower at San Francisco International Airport (SFO). Photo courtesy of SFO

Individual sites will have to set what level of tolerance to allow — in San Francisco, for instance, it has to be quite low because there are hundreds of tracks and some, like the parallel runways that hosted the AC759 near-miss, are only 200 feet apart. That's easier there, though, because SFO has nine sensors to allow for accurate, high-quality data. Looking at data there, Raytheon found that the system could have detected the issue when the plane was about 1.8 miles from the runway, which would have left plenty of time for the controller to act.

"More than likely, they could have moved it to the appropriate runway, instead of what happened, which was the plane got within 13 feet of another aircraft and could have been a very large aviation disaster," Rogers said.

At other airports, the tolerance allowed would be higher than at SFO to prevent unnecessary alerts, which can be a big issue in their own right.

"The one area that is always the problem is false alerts. When there are too many, they lose their significance to the controller," Rogers said. "A lot of our process now is refining the algorithm."

Raytheon is excited about using STARS to solve problems beyond its original scope; the need for a standardized ATM system to be used throughout the NAS got it funded, but now that it's in place, it could be used for a lot.

"Not everyone understood the potential that STARS could solve a problem like this," Rogers said. "Now that it's deployed everywhere, it's a lot easier to support those business cases for making those improvements."

Rogers mentioned helping with departures as another thing the ARV system can do. Sometimes they can be more problematic than arrivals because pilots don't have a runway with which to align themselves.

"When planes takeoff on parallel runways, if they have a preferred navigational route, they are going to try to hit that," Rogers said. Unlike during arrivals, "pilots can't see the runway and center line, and when they're taking off, [controllers] have seen planes takeoff and turn into the other runway's area" where another plane might be taking off.

He said that capability won't be in the 2020 rollout, but it's been talked about and could follow after, as well as other applications for STARS.

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