Ever wonder why there are so many airplanes flying over Maine? Especially in the late morning to early afternoon hours? Are they trying to catch me in my knickers in the garden? Spying on me as I remove that tag from my mattress that warns “Do Not Remove”? Well, the answer is simple (and doesn’t involve any spying eyes or the mattress-police). Our state is just in the right place, at the right time. Or, as the real estate cliché claims, “location, location, location!”
Maine is perfectly located in the path of airplanes entering and exiting North Atlantic Organized Track System (NAT-OTS). (Spend any length of time in aviation and you will see that there’s an acronym for everything. Yes, everything!) Otherwise known as the “tracks” by pilots flying in them. The tracks are an organized way to control the flow of aircraft over the Atlantic Ocean – from one shore to the next. If you’ve been to Europe from the United States, chances are you’ve flown in the tracks.
Each day the tracks operate like a highway to convey flights from one side to the other. But, this highway is never in same place due to the position of the jet stream, wind conditions, and weather systems. And, this highway in the sky changes direction twice a day! During the evening in the United States the flow of the tracks is eastward (towards Europe). Then, in the morning the tracks become westward from Europe to the United States. It is here where Maine sees the most “track” traffic flying overhead. Although when we see them in Maine they aren’t technically in the tracks anymore. The tracks end roughly at 55 W longitude (near Gander in Canada) when radar services are available again. Then, continuing their journey, these flights enter US airspace and continue to their destinations. That’s why when you look up on those brilliant, blue sky days you see multiple contrails lining the sky, all going in the same direction.
This video from NATS is a great time lapse of the tracks, showing east and west traffic as it travels across the Atlantic Ocean in 24 hours.
Ok, so there’s a highway across the Atlantic. How did it get there? The North Atlantic Track Agreement was signed in 1898 (five years before Wilbur Wright, upon winning a coin toss, made the first powered flight in an airplane). This agreement created an organized system for transportation across the Atlantic. No, that’s not a typo – 1898. The first use of such a system was established for commercial shipping. Initially there were seven recommended routes and they were kept at a separation of 60 miles between ships to avoid collision. In fact, the Titanic’s doomed journey in 1912 was traveling on a recommended North Atlantic Track route when it struck an iceberg and tragically sunk. In 1913, the tracks were actually shifted one degree south to mitigate the possibility of iceberg hazards.
Commercial aircraft did not start to use a track system until 1961. By that time, the amount of traffic was growing too steadily and beginning to create difficulties for air traffic control (ATC). In 1965, the publication of the tracks became the standard for navigation across the Atlantic Ocean. Shortly after this the Oceanic Control Area (OCA) was established and split into five areas – Gander, Shanwick, Reykjavik, New York, and Santa Maria. 80% of all Oceanic track traffic passes through the Gander and Shanwick OCAs which hold a boundary at the 30 West longitude line, a rough halfway point between North America and Europe. I’ve also heard this referred to as the “Molson/Guinness” line in terms of beer! Ha!
Aircraft in the tracks are not controlled by radar. This is due to radar being limited to line of sight because of the curvature of the Earth. Pilots in Oceanic airspace use High Frequency (HF) radio and Satellite communications to relay their position and maintain separation with other aircraft in the tracks. Reporting is based on position by latitude and longitude. For every ten degrees of longitude, a pilot makes a reporting that includes position, altitude, and the next two reporting positions on the track route. Over 85% of aircraft flying in the tracks are equipped with Satellite-based CPDLC (Controller Pilot Data Link Communications) which utilizes text based messages to be sent between pilots and controllers.
I’ve been saying “tracks,” plural. Yes, there are multiple tracks that aircraft utilize. They are given letters for reference on flight plans and clearances. Westbound tracks are labeled starting with A, while eastbound tracks are labeled starting with Z. Track messages are transmitted to all operators twice daily so the operators can plan the day’s flights. There are also strict separation requirements while flying in the tracks. Separation on a specific track, say Track E, requires aircraft stay a distance of 60 nautical miles behind and in trail (laterally). This is at approximately 10 minutes apart. There is also a vertical separation in the tracks of either 2,000 feet or 1,000 feet depending upon whether the aircraft has been approved for reduced vertical separation minima (RVSM). To fly in the tracks, aircraft systems are also required to meet specific required navigation performance (RNP) which include redundancy in systems in case of failure or malfunction. So, there are a lot of safeguards established to make flying in the tracks uber-safe!
Usually each track is set at 60 nautical miles apart laterally (equal to one degree of latitude). However, as air traffic continues to increase (both for private and commercial flights) there is a need for more availability to the tracks. To increase traffic capacity and alleviate congestion in the sky “highway”, a system of “half tracks” has recently been established. Instead of 60 nautical miles apart, half tracks are 30 nautical miles apart or half a degree of latitude. Of course, there are even more safeguards and equipment required to fly a half track, including the requirement for CPDLC for communications.
The tracks operate at altitudes between 29,000 and 41,000 feet. When the Concorde flew across the Atlantic Ocean, it operated at much higher altitudes. To accommodate, there were fixed tracks set up; Track Sierra Mike (SM) and Track Sierra Oscar (SO) for westbound flights and Track Sierra November (SN for eastbound flights. An additional track, Track Sierra Papa (SP) was created just for flights to Bermuda! Because the Concorde flew between 45,000 and 60,000 feet there was little weather variation, hence, the need for adjustment for the jet stream wasn’t necessary.
So, when you’re looking up to the bright blue sky and see all those contrails headed in the same direction, you’ll know why – and what direction they’re going! Maine is, for more than one reason, in the right place, at the right time! And, they’re not the mattress-police! Oh and, if you’re wondering – no, I do not conduct nefarious activities in my garden. But, I did remove the tag from my mattress!
Blue Skies and Happy Easter!