Good morning,
Air traffic controllers would like to correct some misinformation being distributed by the airlines’ trade group’s PR machine.
In a Chicago Tribune “Travel Insider” column on August 5 about flight delays and the discussion about how a Next Generation air traffic control system could help, columnist Alfred Borcover paraphrased Air Transport Association Spokesman David Castelveter as saying, “Countries such as Canada, Australia and the United Kingdom are using next-generation precise satellite systems that permit much less than the normal 3 miles separation between planes.”
Sounds good. Except that it’s not true. There are only four places in the world where aircraft are allowed to legally be closer than three miles:
London Heathrow, but only during the daytime in good weather within 15 miles of landing, the United States at most major airports within 10 miles of landing, one terminal area in Sweden, and in Mr. Castelveter’s imagination.
The National Air Traffic Controllers Association asked its controller colleagues in other countries about their separation standards between planes, even when using advanced navigation technologies, and here is what we found:
While the technology is there, the standards that they have to use to separate aircraft remain the same – three nautical miles — restricted by the reality of controllers being able to intervene with any real possibility of maintaining safety. Says our contact there: “While we love RNP (Required Navigation Performance, a modern GPS navigationsystem) approaches and all they offer the industry, we still use three nautical miles.” And here’s more: “ADS-B (Automatic Dependent Surveillance – Broadcast) separation procedures similar to radar separation minima are implemented for en-route traffic. ADS-B separation procedures for non-radar terminal areas are being developed, but minima would not be less than the radar minima.”
Our contact says, “Satellite navigation can be used as one means of navigating for P-RNAV (Precision Area Navigation). However, the route spacing to be applied when using P-RNAV is five nautical miles for straight segments, and more for converging routes. The proposed route spacing is therefore still greater than the three nautical miles that can be achieved when applying radar vectors in the LTMA (London Terminal Control Area).”
Our contact notes that RNP procedures in terminal airspace could eventually enable routes to be spaced by as little as 1.2 nautical miles “using the principle of containment, rather than traditional separation standards.
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However, in practice, such low route spacing values won’t be achieved due to the need to maintain the ‘controller intervention buffer’, i.e. provide time for controllers to detect a blunder, formulate a corrective course of action, apply the corrective course of action and the aircrew respond to the corrective action. This buffer will, in my humble opinion, prevent routes from being spaced less than the three nautical miles that is already in use in some terminal airspace.”
Here’s what a Canadian air traffic controller wrote in the Tribune’s “comment” section beneath Mr. Borcover’s column: “As a Canadian air traffic controller, I can assure you that we are still using old radar systems with a minimum separation standard of three miles, with five miles being the standard the majority of the time. We are in the very beginning of looking at using satellite surveillance but it is not in use at this time.”
SOUTH AFRICA: South African controllers use five nautical miles as the minimum radar separation. “We are working to reduce to four nautical miles on final,” our contact says, “but it’s not approved yet. This is just radar and no fancy RNAV/RNP/GNSS in this process.”
Separation standards are the same as the United States’:
Five nautical miles for en route airspace and three for terminal airspace.
“There is discussion around reducing the en-route minima towards three nautical miles with RNP,” our contact says, “but this is still only an idea and would be some time away.”
Separation standards of three nautical miles are used ONLY in the terminal airspace of Rome and Milan. More separation is used everywhere else.
Separation standards are five nautical miles for en route and three nautical miles in terminal, except for one area where 2.5 nautical miles is used.
Doug Church
Director of Communications
National Air Traffic Controllers Association
202-220-9802