One late afternoon probably very soon visibility will deteriorate over Philadelphia, and a critical experiment for the future of the NextGen air traffic modernisation system will begin.
Despite the marginal visual flight rules (VFR) conditions near twilight, the controller in this future scenario will ask the crew of a US Airways A330 to visually confirm they can see a small regional jet lined up just ahead of them.
The crew of the A330 follows procedures. They see the regional jet more than 3nm (6km) ahead and slightly below them, and confirm the information to the controller.
After briefly ducking their heads to review the approach checklist, however, the A330 crew looks up and finds they have a problem. No matter how they strain their eyes, they do not see the regional jet anywhere.
If this were any other A330, procedure dictates the red-faced crew to inform the controller that they have “lost” the regional jet. This then requires the controller to order the A330 to go around, costing the airline extra money for fuel and possibly making passengers late for connections.
But this is not any other A330 – it is one of the 35 US Airways aircraft equipped with a new, NextGen-derived tool called the cockpit display of traffic information (CDTI) assisted visual separation (CAVS) application. Instead of flying a go-around, this A330 crew consults the CAVS display, and – with the controller’s permission – automatically reacquires the regional jet’s position. The regional jet lands, the A330 follows just behind and the passengers make their connecting flights.
At least, that is what is supposed to happen. In September, US Airways started equipping all of their A330s with the ACSS SafeRoute system – the first avionics product designed to exploit the more accurate positioning data provided by NextGen.
SafeRoute features four applications, including CAVS, mergers and spacing, in-trail procedures and surface area movement management.
“It’s taken quite a bit of work, but we’re excited that we finally have a product now,” says Ron Thomas, managing director of flight technical operations for US Airways.
The airline is rolling out the capabilities gradually. Activating all four applications at the same time would be deemed a complex upgrade by the US Federal Aviation Administration, requiring US Airways to cycle all roughly 200 A330 pilots through simulator training over a 13-month cycle, Thomas says.
The systems installed to date are just being used to get the crews acclimated. By February, US Airways plans to activate CAVS as the first SafeRoute application.
CAVS is the “easiest of the functions to use”, Thomas says. “So, now, to help them with visual acquisition, they’ve got this device that says the traffic is exactly this distance and this location.”
In a larger sense, SafeRoute puts a key element of the entire NextGen air traffic modernisation system on trial. No one doubts that the FAA will benefit by retiring a maintenance-intensive, radar-based control system with modern, more accurate technology.
The question airlines have asked is "what’s in it for them"? “The jury is still out on that,” Thomas says.
The FAA is spending $1.8 billion to convert the national air space to a more accurate, satellite-based traffic control system.
The technology underpinning the new system is the automatic dependent surveillance system – broadcast (ADS-B). This allows the aircraft to broadcast information about its position every 1-2s – much faster than the 10-15s refresh rate of a radar-based system.
More accurate data means controllers can space aircraft closer together, increasing the capacity of the national airspace almost overnight – in theory.
There is one big problem with the FAA’s plan, however. The system depends on equipping every aircraft in the system with a new transponder called ADS-B Out. There are an estimated 42,000 commercial aircraft in the worldwide fleet, each equipped today with two non-compliant transponders.
The FAA has mandated that all aircraft re-equip with ADS-B compliant transponders by 2020. The transponders have to be certificated under a standard known as DO-260B. Nearly five years after the FAA issued the mandate, the only transponders that meet the standard on the market today are the NXT-600 and NXT-800 transponders made by L-3 Communications ACSS.
The FAA mandate will take effect in six years, but so far only 194 commercial aircraft in service today are equipped with ATS-B Out-compliant transponders. That leaves barely half a decade to equip nearly every commercial aircraft with a pair of compliant transponders, including the ACSS system and forthcoming offerings from Rockwell Collins and Honeywell.
“Start to do the math. You’re going to have a little problem,” says Stephane Chartier, marketing manager for ACSS – a joint venture between L-3 Communications and Thales.
The challenge becomes even more stark when airlines factor in the change to make the conversions. The Airbus A320 fleet seems to be a relatively simple change. ACSS installed ADS-B Out transmitters on the JetBlue fleet as an overnight operation. However, other aircraft types may not be so easy.
Some airlines have reported that their aircraft will need to install transponders during C-checks, requiring an at least five year interval to complete installations across the fleet.
Airlines have several reasons to be slow to install the ADS-B-compliant transponders – not least the lack of a certificated product until the ACSS equipment appeared earlier this year.
“Technically, ADS-B Out doesn’t do anything for the airline,” Chartier says. “United Airlines has to put the airplane down during a C-check [to install the equipment]. This is a pain in the butt.”
The FAA is mandating that users of the airspace install the ADS-B transponders, but that does not mean the agency cannot try to make the bill easier for airlines to digest.
In fact, the FAA has opened preferred routes for airlines that operate with ADS-B-compliant equipment. So far, that has been an advantage exploited almost exclusively by JetBlue, which had a subset of its A320 fleet upgraded under another FAA-funded demonstration programme.
“This is what [the FAA] calls, ‘best-equipped, best-served’,” Chartier says.
In the Gulf of Mexico, for example, the FAA has installed ADS-B ground stations on oil drilling platforms, providing a surveillance capability where none before existed.
On bad weather days, airline routes that normally cross the Gulf of Mexico are redirected by the FAA overland. The weather-induced change means delays on the ground as crews re-plan their routes on longer and less-efficient flights around the weather.
JetBlue’s A320s, however, are allowed to skirt the edges of a weather system over the Gulf of Mexico, as the FAA’s newly-installed ADS-B ground stations are able to track them from take-off to landing.
“There was no waiting on the ground,” Chartier says. “They go their expected time of departure, and then when they got around the weather, they let them fly over and they got there and they saved 100nm from that trip.”
These incremental benefits are available to airlines before the mandate takes effect in 2020. Beyond that date, the benefit of NextGen to airlines may be defined by the success or failure of ADS-B In – aircraft receiving the ADS-B data.
There is an inescapable chicken-and-the-egg debate in any discussion about the future of NextGen. The success of technologies such as ADS-B In depends on the rate the equipment is installed. Until ADS-B In reaches critical mass, however, airlines have little incentive to spend money to equip their fleets.
“Where that turning point [is] has been a topic of discussion for as long as I’ve been in the company,” Chartier says. “This is all the dreams of the FAA – and we’re banking on those dreams to happen – but you need to have everybody equipped.”
In a fully-equipped air traffic system, SafeRoute is a potential game-changer for airlines.
The CAVS application allows airports to delay the daily switchover between VFR approaches and instrument flight rules (IFR), increasing landing capacity and reducing delays.
The in-trail procedures application narrows separation distances for aircraft flying in the same direction at the same altitude.
The mergers and spacing application means aircraft can be precisely arranged to be evenly sequenced on approach to an airport, eliminating the need for aircraft to fly holding patterns or downwind legs until an approach path is available.
Finally, the SAMM application improves situational awareness of pilots on the tarmac, and reduces the chance of incursions, excursions and other ground hazards to airlines.
The technology holds much promise, but there are glitches that must be overcome. If the technology is widely adopted, for instance, the frequency could be overloaded by users, causing the signal to drop out.
“If there’s so many [aircraft] on the frequency it can cause a drop-out,” says US Airways’ Thomas. “We’ve identified that if you bring the whole [national airspace] into it, there may be a problem.”
But frequency experts are already developing technology to mitigate the problem. Software is being developed to allow the ADS-B In signal to use frequency-hopping techniques, which dramatically increases the throughput of the signal, Thomas says.
Another problem affects the SAMM application. On airports with crisscrossing runways, obstacles such as buildings sometimes creates distortions in the frequency.
Operators, however, may accept some imperfections if the signal improves the situational awareness of their pilots on the ground.
“My opinion – and every pilots’ opinion that’s done it – is 'so what if it’s not perfect',” Thomas says. “It’s way better than what we have today. Today you have nothing, so we are more than happy to live with any imperfections in the system when you look at in aggregate and it’s safer than the operation today.”
US Airways and ACSS also have to live with some imperfections in the execution of the SafeRoute demonstration.
The ITP application, for example, depends on having two ground stations – Reykjavik, Iceland and Shanwick, Scotland – online, but only the Icelandic station is equipped to fully participate.
That means US Airways A330 crews participating in the demonstration and flying over Shanwick have to indulge in a game of pretend. ITP allows aircraft to climb to a higher altitude, which improves fuel efficiency. The crews are equipped with a display that shows all traffic up to 160nm ahead of them, versus only 40nm with the existing terrain collision avoidance system.
First, however, the crews must request permission to move to a different altitude. As Shanwick lacks the necessary ground equipment, they are unable to accommodate the request.
The Shanwick station “will take the request but then deny it, which is extremely frustrating”, Thomas says. “We had really expected that by now they would have got the ground equipment that would satisfy them.”
However, the Shanwick station has agreed to log all requests, in an effort to build a proper database for the demonstration.
“That’s where we have to plead with our pilots to say, ‘Please, I know they’re going to say no,’” Thomas says. “But they’re doing something with this data. They are actually not only tracking how many times it’s requested, but how many times they would have been able to accept it when it comes in.”
On the other hand, US Airways believes more data will be needed before airlines have enough information to build a business case to invest in ADS-B In.
Ideally, the FAA would select one or two operators for a follow-on demonstration. The experiment would equip the majority of aircraft types that fly into a major hub, so that the airline has a better than 50% chance that it will have enough aircraft in the traffic to use, for example, the mergers and spacing application, Thomas says.
“That would be my request,” Thomas adds. “ I don’t know if [the FAA] can or will, but I can tell you in order to get over this hurdle they probably are going to have to do that.”