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North Atlantic Airspace OTS NIL Initiative Ends as NATS and IATA Study the Benefits

Will the Organized Track System be eliminated from the North Atlantic airspace system?

NATS, the air navigation service provider for the UK, has ended its initiative, OTS NIL, introduced in March to eliminate the Organized Track Structure (OTS) in the North Atlantic's oceanic airspace. Now, the company is working with airlines and NAV Canada on a long-term plan that could permanently eliminate the tracks while upholding the data link mandate and taking advantage of expanded surveillance from space-based ADS-B.

Jacob Young, the operational performance manager for NATS, told Avionics International that the initiative was undertaken by the organization amid lower levels of North Atlantic traffic and the more robust surveillance of traffic provided by space-based ADS-B.

"Space-based ADS-B lead to us making this decision,” Young said. “We'd already been looking at this before COVID, and had conversations about it with airlines prior to COVID. What COVID did, with the lower levels of traffic, was to accelerate that from a place that we were talking about three to four years down the line to saying why not try it now? [International Air Transport Association] IATA reached out to us requesting it, and we were able to tactically and procedurally prove that we can do it.”

Young first announced the decision by NATS to launch the new initiative in a Feb. 3 blog that provides an understanding of how the North Atlantic Track system works. In the oceanic airspace for aircraft flying from North America to the UK and Europe, since the 1960s, air traffic controllers on both sides have used 12 tracks that change twice daily to account for winds.

When airlines file flight plans, controllers clearing them from UK or Canadian airspace and into the oceanic routes try their best to slot them into the track that matches their intended trajectory. These tracks are sets of waypoints within the North Atlantic airspace that try to take advantage of the jet streams going in each direction.

NATS started its initiative to eliminate the east and westbound tracks on days where traffic was lower in March. At that time, the North Atlantic airspace was seeing an average of 500 flights per day compared to the normal 1,300, according to Young.

That made it an optimum time to see if flights are shorter and faster when airlines are asked to flight plan based entirely on their aircraft's optimum route, speed, and trajectory.

The decision to temporarily stop the OTS NIL plan was driven by rising levels of traffic in the North Atlantic, where Young says Shanwick controllers are seeing an average of 850 to 900 flights a day right now. NATS is projecting up to 1,100 flights per day in Shanwick airspace—the portion of the North Atlantic controlled by NATS—in September. He described the difference between having the tracks and not operating them as leading to a much more randomized route structure with more flights "crisscrossing" and controllers shifting from tactical to a much more strategic workflow.

The track elimination policy on lighter traffic days officially stopped on July 1, Young said. Lessons learned by controllers during the four-month period featuring periodic OTS NIL days will be summarized in a report that NATS UK is currently working on with IATA.

There are several near-term policy changes to the tracks that are being considered.

"In the short term, we're looking to do things like remove flight levels from the tracks on a permanent basis and to potentially put a max cap on the footprint of the track as traffic levels start to grow again,” Young said. “And we're looking to investigate things like chopping down the time of the tracks. That's all hopefully in the next 12 months. A little further down the timeline is when we'd look at how could we possibly introduce OTS NIL on a permanent basis. There's a bit of procedure that we need to continue to study in order to make this a reality during higher levels of North Atlantic traffic.”

March 9, 2021 was the first day of the OTS NIL initiative, which lasted until July. (NATS UK)NATS UK.

Young's February blog post referenced a study published by the University of Reading in January that received a substantial amount of media coverage. The study analyzed around 35,000 flights between New York and London in both directions Dec. 1, 2019, to Feb. 29, 2020, and concluded that "taking better advantage of the winds would have saved around 200 kilometers worth of fuel per flight on average, adding up to a total reduction of 6.7 million kilograms of carbon dioxide emissions," according to Young's blog.

The study emphasizes a need to keep aircraft speed and altitude constant to keep a consistent fuel flow rate per unit time. Keeping these aspects consistent ensures the route with the least distance involved is used based on a trajectory optimized for the aircraft’s weight and cruising speed. While NATS has stopped its OTS NIL initiative temporarily, in the long-term it could come back into effect once all of its positive and negative aspects are understood.

NATS is currently still actively working through OTS NIL scenarios with simulated exercises.

"What we're doing now is we're continuing with a tabletop exercise with a number of the key airlines in the north Atlantic. We’re running tabletop exercises where we simulate traffic in the North Atlantic based on 2019 levels—right around 1,500 to 1,600 flights a day. We get airlines involved to give us a couple of flight plans that feature routing based on if the tracks are there and if they were not,” Young said. “Based on the simulated flight plans, we’re looking at the fuel burn difference between those and putting a bit of air traffic control weighting on that. During the exercises, we’ll actively try to figure out what's the likelihood of you getting an entry point change or flight level change. By the end of this year we intend to produce a report which says, this is what we see will be the efficiencies from introducing OTS NIL.”

The timing of the introduction of OTS NIL in the North Atlantic's oceanic airspace system came at the end of another temporary policy that was established in the airspace over the last year because of the impact of COVID. In March 2020, the FAA and its partners in the North Atlantic Systems Planning Group endorsed a plan to temporarily terminate the North Atlantic Data Link Mandate (DLM) due to decreased operations as a result of the global COVID-19 crisis.

DLM requires aircraft flying between FL 290 and FL 410 in the North Atlantic airspace to be equipped with future air navigation system (FANS 1/A) avionics, consisting of controller-pilot data link communications (CPDLC) and automatic dependent surveillance-contract (ADS-C) to enable controllers to monitor and communicate with flights or reduce aircraft separation distances in areas where radar is not feasible. ICAO published an operational bulletin in February giving official notice of the ending of the data link mandate relief policy enacted last year.

Only certain areas of the North Atlantic are exceptions to the DLM, including all airspace north of 80°North, the New York Oceanic East Flight Information Region (FIR) as well as Tango Routes T9 and T290. Aircraft not equipped with data links can still request to climb or descend into DLM airspace but are only accepted based on the individual decision-making of the relevant air traffic controllers.

Young said that NATS still occasionally gets a request for access to DLM-mandated airspace, but that they're rare.

"We still see the occasional requests for flights, trying to come into the airspace when they're not equipped, but I think most airlines have understood the mandate,” Young said. “The only ones we tend to get now will be the odd transfer flights or maintenance flights, or somebody who hasn't transited the ocean for some time will make a request.”

The next steps in determining how to use the OTS NIL policy on a permanent basis will focus on understanding the benefits that the policy will bring to airlines. NATS and IATA hope to have a report summarizing the benefits by the end of the year.

“Our focus is 100 percent centered around establishing what the benefits are for airlines. Once we know everything we can about the benefits, we can apply the policy to the entire NATS airspace, not just the ocean,” Young said. “All of our focus right now is on what benefits we can bring to the customers at a time when we have lower traffic levels? And if we can keep that going into the future, we will.”