ATM Modernization, CNS, Commercial

Reduced Separation Over North Atlantic Track System is Coming

By Woodrow Bellamy III | October 12, 2016


[Avionics Magazine 10-12-2016] The process of managing separation between aircraft over the North Atlantic is about to change drastically. The North Atlantic Tracks (NAT), the oceanic airspace where aircraft fly passengers and cargo primarily between North America and Europe, is the busiest oceanic airspace in the world, featuring an average of 1,200 aircraft per day. Once aircraft get beyond the reach of ground-based surveillance on the coastal areas of each side of the NAT, they are managed by using air traffic control rules that require large spacing between them, and controllers rely on voice or data link communicated position reports to maintain separation. However, as John Crichton, chairman of space-based surveillance company Aireon explained during a speech at the International Aviation Club last week, within the next two years, managing aircraft separation could see a huge overhaul. 
 
 
NAV Canada Gander Oceanic ATC Technology. Photo: NAV Canada.
 
Over the North Atlantic there is no radar coverage allowing for air traffic controllers to detect the exact position of an aircraft. To overcome the lack of radar, air traffic planners in Gander, Newfoundland and Prestwick, Scotland publish a set of 10 or more North Atlantic tracks everyday. These tracks are sets of waypoints within the North Atlantic airspace that that take advantage of the jet stream to Europe to use the strongest tail winds and reduce fuel consumption. 

 
Aireon, a joint venture between Iridium, and Air Navigation Service Providers (ANSPs) NAV Canada, Denmark’s Naviair, Italy’s ENAV and Ireland’s IAA, will begin operation of 81 space-based Automatic Dependent Surveillance-Broadcast (ADS-B) 1090 Extended Squitter receiver payloads to enable global air traffic surveillance across the Iridium NEXT generation constellation of 66 cross-linked Low Earth Orbit (LEO) satellites in 2018. By enabling the remittance of position reports from 1090 MHz ADS-B-equipped aircraft flying over the NAT to the Iridium satellites and down to Air Traffic Controllers (ATCs) managing the airspace, controllers managing the North Atlantic Tracks can start to apply the type of ATC rules that are used in domestic airspace. For example, in the U.S., most of the en route airspace features separation standards for aircraft of 1,000 feet vertically and 5 nautical miles laterally. The lateral separation drops to 3 nm in properly equipped terminal areas, according to Crichton.
 
"Out over the oceans we lose surveillance and must revert to what is called procedural control: a bubble of protected airspace about 60 nautical miles in radius must be kept around each aircraft. Safe? Absolutely. Efficient? No," said Crichton. 
 
The average distance across the North Atlantic outside of surveillance is about 1,500 nm, so within one North Atlantic Track at that length today using the current 60 nm spacing permits about 25 aircraft into one track at one time, Crichton explained. If the domestic 5 nm standard were available, that number would increase to 300 aircraft. At 15 nautical miles it would be 100 aircraft and at 10 nautical miles it would be 150 aircraft, he says. 
 
"Work [that] Aireon and its partner ANSPs has done with 10 of the largest North Atlantic airlines shows a preliminary average savings per flight of about $800 due to operational efficiencies space-based ADS-B will enable.   That is average. Modeling by some carriers indicates they may save $1,400 per flight in fuel. Using the $800 average and based on current traffic volumes, this would amount to over $300 million per year, every year and grow in the future," said Crichton, noting that this estimate was based on today’s low fuel prices. 
 
Aireon isn't the only entity working to reduce the current separation requirements featured in the NAT region. In fact, their global spaced-based ADS-B surveillance system will only enhance research NAV Canada is already conducting in the region. In September, NAV Canada released an update on its Reduced Lateral Separation Minimum (RLatSM) project, the first phase of which commenced in December 2015. 
 
The RLat project is an ICAO initiative that was implemented by NAV Canada, initially introducing one additional track where a half-degree of 25 nautical miles, instead of the one degree 60 nautical mile separation route was used. The first phase of RLatSM was a success, proving that aircraft equipped with Controller-Pilot Data Link Communications (CPDLC) and Automated Dependent Surveillance-Contract (ADS-C) equipment could be separated by 25 nautical miles instead of the required 60 nautical mile separation requirement that is currently standard. 
 
"RLatSM Phase 2 will expand the implementation throughout the entirety of the NAT Organized Track System (OTS) between FL 350 and FL 390 inclusive. As notified in state letter EUR/NAT 16-0345.TEC (NAE/DAC) (dated 18 July 2016), Phase 2 will begin on or soon after 10 November 2016," NAV Canada said in a statement in its September update on the program. 
 
While the expansion of the RLatSM concept to the entire NAT can increase the number of aircraft that can fly within each North Atlantic track, the introduction of space-based ADS-B in 2018 will lead to even more reduction in separation. 
 
According to Crichton, the cost of providing the space-based ADS-B service, once available, will amount to a portion of the previously mentioned fuel savings. 
 

"Aireon’s cost of providing this service would amount to a small part of these savings. And Aireon’s charges are scaled to the actual benefits in various types of airspace throughout the world. In other words, Aireon’s cost of service will be substantially less than the benefits generated. Moreover, and most significantly, with no new equipage costs for airlines," said Crichton.  

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