North Atlantic Tracks
This may be a silly question. I was looking at the North Atlanic tracks on a regular map. When I transpose the tracks onto a globe, they make a curve or arc across the ocean. When flying these routes, is the aircraft in a very, very slight continuous left or right bank for a longish period or are the routes flown in a series of straight lines over the earth's curvature with an alteration of heading now and then.