Suddenly I see

NATS explains that live trials began on 29 March, about two months after the Aireon switch-on and says the early results are promising. The trial involves Nav Canada overseeing the Gander Oceanic Flight Information Region (FIR) and the UK’s NATS on watch over the Shanwick FIR. These are the two contiguous sectors that carry very nearly all the traffic flying both ways between North America and Europe/ Middle East.

The early results are looking very positive, conferring safety validation for smaller traffic separations and a hugely increased probability that aircraft will be able to be cleared to fly at their chosen speed and best height.

Until now, aircraft flying between North American and Europe had always been invisible to ATC once they were more than about 350km off the coast on either side, because at that distance from radar antennae they had disappeared over the radar horizon. ATCOs, however, still knew approximately where each aircraft was because each aircraft reported its position, height and a time estimate for the next reporting point every 14min or so. Once done by voice, this information has more recently been transmitted via ADS-C (ADS – Contract) every 1014min using a FANS (future air navigation systems) datalink. FANS has become a misnomer – the system is no longer the future, though it may remain the present for some time in other oceanic areas.

Under the FANS system aircraft were carefully released into their pre-cleared, one-way oceanic tracks at specific heights, time intervals, and speeds, so they would maintain separation vertically and horizontally. Now, NATS explains, position updates are rapid and frequent: ‘The changes we’ve made to our ATM system have received a warm welcome from our controllers, while our new Aireon service has delivered 134m ADS-B reports since the end of March, all of which arrived within the target update rate of eight seconds, with most as low as 2-3 seconds. The average time taken for these reports to reach a controller was just 0.19 seconds, well within our target of two seconds or less.’

The 14min position/performance update rate provided by the old FANS system is an enhanced version of a welltried voice ATM methodology known as procedural control and most of the world will continue to control oceanic air traffic procedurally for some years yet. In fact only 30% of the Earth’s surface has radar coverage enabling aircraft surveillance for ATM purposes, and ADS-B is increasingly also used to cover large wilderness areas in some countries like Australia but at present they have ground-based, not satellite, data-link relay systems.

On 28 March, less than two months after Aireon’s switch-on, live ADS-B surveillance trials involving Nav Canada and UK NATS began on the busy North Atlantic (NAT) routes. The trials are endorsed by the International Civil Aviation Organization (ICAO).

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Increased aircraft trafficking

Comparing NATS’ traffic in the period 28 March and 31 August 2018 with the same this year, 4,400 more flights were assigned their requested level and, by the end of the year, it is anticipated that 90% of flights will get what they ask for. Over that same period, explains NATS: ‘We were also able to assign 3,419 more flights their (requested) route, while around 43,000 flights – over one-third of all eastbound traffic – were instructed to ‘Resume Normal Speed’ for a total duration of 2.2m minutes, or 37,000 flight hours. Flying at ‘normal’ speed allows crews to fly at the speed that best suits them, enabling flexibility to speed up, slow down to meet their schedules, or simply to fly at the most economical speed instead of the totally fixed speed we’ve had to operate for decades.’

To give an idea of the size of the annual task, the number of flights passing through the NATScontrolled Shanwick OCA in 2018 was just over 500,000 flights.

At present these flexible speed clearances – known as OWAFS (operations without fixed assigned speed) – are still issued manually by ATCOs where they see opportunities and where workload permits but NATS says they will be automated by the first quarter of 2020. ATCO-pilot communications are normally by controller-pilot data-link communications (CPDLC) exchanging keyboard-generated messages, although voice is available.

NATS’ Head of Strategic Oceanic Engagement, Andy Smith comments: “We’re seeing the beginning of the end of the organised track structure (OTS). The OTS was introduced decades ago, itself designed to add additional oceanic capacity with a series of set routes designated each day, taking into account the location of the jet stream, to permit aircraft to efficiently cross the North Atlantic.” Of course, crews will continue to choose the most efficient routes to minimise headwinds or take advantage of tailwinds but the NATS area will gradually become free-routing airspace.

Smith explains: “Being able to reduce separation standards and offer greater flexibility on routes, speeds and levels means 62% of traffic now doesn’t need to use the OTS at all, compared with 50% in 2015. That’s a trend we will now see accelerate, as we continue to unlock all of the service improvements available to us through Aireon and our deployment of our new standards. Over the coming years, we estimate that 90% of airspace users will be assigned their requested trajectories, something that will support the progressive reduction and eventual removal of the OTS.”

Resulting annual fuel savings on the North Atlantic at this stage of the trial are expected to be 38,800 tonnes. As experience with the system increases, and if validation analyses continue to prove margins are safe, further improvements may be gained.

Increased safety​​

The possession of radar-like surveillance capability improves safety as well as efficiency, and enables much more precise monitoring, recording and analysis of traffic behaviour, enabling the identification of risk and of potential improvements in best practice Previously, if an aircraft began to deviate from its cleared track because clearance details were misunderstood or entered incorrectly into the flight control panel (FCP), it could take up to 14mins before ATC got a position update revealing the error.

Another benefit of the new datalink is that it goes beyond providing aircraft position and speed, it can indicate the crew’s intention by detecting pilot input to the FCP to change the aircraft’s flight level or heading. So if, for example, the flight level selected is incorrect according to the aircraft’s clearance, the ATCO will receive a warning before the error has been actuated.

Controllers managing the Shanwick Oceanic sector sit at a HMI (human/machine interface) display which, to the unpractised eye, looks identical to those used by controllers working the Scottish domestic sectors in the same operations room at NATS’ Prestwick Centre, except the latter are using secondary surveillance radar (SSR) input rather than ADS-B reports.

As Smith explains, the oceanic controllers are assisted by automation and, therefore, do not have to monitor every aircraft return all the time, enabling them to monitor larger numbers than they used to be able to handle safely. Clicking on any contact will provide information on the 12 closest aircraft. The system provides automatic warning to the controller of any emerging medium-term conflicts and – if more than one conflict – they are prioritised.

At work the oceanic controllers are quiet most of the time, occasionally checking a particular contact that looks clear of traffic to see if it could be relieved of any restrictions to its clearance. If it proves clear, the controller taps into the datalink keyboard ‘resume normal speed’, or passes the crew a level change clearance if it was being held down.

At present the live trial in Gander and Shanwick Oceanic continues but all the signs are it is working to specification or beyond. Back in February 2019 Aireon CEO Don Thoma was able to boast that: “For the first time in history, we can surveil (sic) all ADS-B-equipped aircraft anywhere on Earth.” Not all the world’s ANSPs are ready for it yet, but those who are ready – in addition to Nav Canada and NATS – include the Irish Aviation Authority, Italy’s Enav and Denmark’s Naviair.

Aireon begins tracking the world

The European Union Aviation Safety Agency (EASA) is also working with Aireon. It is in the early stages of trialling the provision – by Aireon – of space-based surveillance over the whole continent, with the ADS-B data relayed to Europe’s ANSPs. Thoma describes Aireon’s core product as “global surveillance as a service”. When and if that is approved in Europe, it will be another first: the provision of surveillance data to ANSPs by an organisation that is a business, not an ANSP, nor the military.

Meanwhile, surveillance is not the same in the US’s oceanic areas of responsibility, even where they border with Gander Oceanic. Although the Federal Aviation Administration (FAA) is thoroughly familiar with the use of ground-based ADS-B for surveillance, it has not deployed it for oceanic areas. The FAA’s Capital Investment Plan sets out the agency’s plans to deploy ground-network-based ADS-B surveillance gradually to replace SSR over land and in coastal areas beginning in 2020 and it already uses it extensively in the Gulf of Mexico for managing oilsupport helicopter operations.

Bordering Gander Oceanic to its south is the New York Oceanic FIR. It does not have the same capabilities for reduced separation that Nav Canada and NATS offer in their oceanic FIRs. They have a system similar to the one the latter two ANSPs have just replaced, based on ADS-C relayed via FANS datalinks, enabled by Inmarsat.

The FAA’s long-term intentions for ADS-B in Oceanic areas are not yet defined. It does say, however: ‘The Reduced Oceanic Separation (ROS) – Advanced Surveillance Enhanced Procedural Separation (ASEPS) program will re-examine current limitations to reducing oceanic separation standards by evaluating improved surveillance capabilities, including space-based ADS-B and enhanced ADS-C with a faster update rate than available today (a 3.2min update rate is planned)… the program is working towards a financial investment decision.’

When NATS, however, was reviewing enhanced ADS-C as an upgrade option it found that, while it provided the potential for smaller separations than the non-enhanced variant, safety improvement was limited by the fact that an ADS-C report takes minutes to download, whereas ADS-B takes less than a second. The FAA’s decision will probably be influenced by the simple fact of the lower traffic density in its oceanic airspace. On both the USA’s Atlantic and Pacific shores the airspace is indeed busy but much less so than the North Atlantic sectors that Nav Canada and the UK manage.

NATS summarises the project: ‘The North Atlantic is the busiest piece of oceanic airspace anywhere in the world, acting as Europe and North America’s transatlantic gateway. What we’ve developed here is important not just for the airlines that use it but for the wider industry worldwide with our deployment of new standards and transformational new technology yielding safety, capacity and environmental performance improvements that we’re sharing with others.’