Here is an image of one of my calibrated maps from PlanePlotter. You will see in this image how jet aircraft fly along assigned jet airways. Basically they are highways in the sky and in general all flights use the same airways. The only flight in general that uses a different route each time is QF63 to Johannesburg which uses a flex route which sometimes sees it fly just south of Mebourne then accross the bight, whereas other days they can be seen down the west coast of Tasmania and right down into the Southern Ocean.
