Every day, over 2000 aircraft travel across the Atlantic ocean, bound for North America or Europe on the North Atlantic Organized Track System. Have you ever wondered how pilots navigate and communicate during the journey? Communication over the Atlantic is an interesting combination of modern digital messaging, satellite communication, and the early 1900’s low-tech!
To accommodate the twice-daily stampede, air traffic planners in Gander, Newfoundland and Prestwick, Scotland create weather optimized routes across the Atlantic, called the North Atlantic Organized Track system (NATs). NATs are like a multi-lane, one-way highway in the sky. The tracks change each day to provide the most efficient routes for the airlines. A track NOTAM (Notice to Airmen), also called a “track message,” that defines each day’s tracks is published online.
Airline dispatchers and pilots use the published tracks to plan the day’s flights. Each track is labeled by a letter to make it easy to reference on a flight plan. Westbound tracks are labeled A, B, C, D, etc. Eastbound track labels are at the end of the alphabet (W, X, Y, Z).
Every day, from 0100z–0800z (8 pm–3 am EST) hundreds of airliners fly eastbound from North America to Europe. From 1130z–1900z all that traffic flies back to North America. Why those times? Because that’s when most passengers want to fly these routes.
About 30 minutes before a flight departs, the crew contacts air traffic control to receive a route clearance. For most domestic and trans-pacific flights, ATC issues the crew a complete route from start to finish. For atlantic crossings, the route clearance covers the beginning and ending domestic portions of the flight which includes a series of coordinates of latitude and longitude like 52N30W. Even though they have been assigned a particular track in their flight plan before departure, the crew receive their final oceanic clearance only 30-90 minutes before entering the oceanic airspace for the track they have been assigned on ground.
There’s no radar over the ocean, but oceanic controllers must still make sure all the aircraft are safely separated by distance and altitude. Since they can’t “see” the aircraft, controllers rely on pilots to report their position at regular intervals. A position report provides an aircraft’s location, speed, and altitude so the controller can build a 3D picture of all the traffic. In the old days, pilots reported their position by HF radio every 10° longitude. Now it’s digital (and much easier).
This is an example of a message sent to a pilot from the ATC, this communication is also known as Controller-Pilot Data-Link Communications (CPDLC):
ABC123 CROSS 50N040W AT OR BEFORE 1428
AFTER PASSING 50N040W MAINTAIN MACH 0.82
The meaning is, “Flight ABC123 is to adjust its speed to ensure that the flight will reach the coordinates 50N 040W no later than 1428 UTC. After passing coordinates 50N 040W, the flight is to maintain speed Mach 0.82.