… and yet it’s by far the most likely one. Before each flight, the cockpit studies winds and weather conditions and identify the best route on that basis. For routes like lhr-sin given existing limitations, a small difference in winds can tip the balance between a routing over the Persian Gulf or Central Asia, and both happen as a result.

More exciting though, on a routing like icn-hel, a small difference in winds will make the best routing go over China and Central Asia… or completely opposite over Alaska and the North Pole.