Background: The North Atlantic Tracks System is a system of pre-designated flight paths that are often used during transatlatic crossings, where radar coverage cannot be used for traffic control. Their path changes from one day to the next, based on polling of the participant airline desired routes.

Autoritative source for NATS: FAA

Easier to use source: NATS map , SkyVector (Open Layers, Nav, North atlantic, West)

Westbound track are lettered from A to D-E-G, depending on the number of tracks opened that day. They are published 2200 UTC the day before.

Flying over greenland is defined as at least one track path being, for any distance, higher than latitude 60N, and between 40W and 60W - see the following: