When we think of the shortest distances between two cities, our brain tends to work in two dimensions, which ignores the fact that the Earth is a sphere.
The shortest distance between those cities – which is the route an airline wants its planes to fly – is a curve when represented on a map rather than a sphere.
To travel the shortest distance between two points, aircraft follow that curve, known as a great circle route.
For example QF27, the Qantas flight between Sydney and Santiago, travels deep into the Southern Ocean, and nowhere near Auckland, which would appear to be a waypoint between the two on a map.
When Singapore Airlines re-starts its non-stop service from Singapore to New York later this year, the eastbound flight will take about 18 hours.
However, the flight time from Singapore to San Francisco is 16 hours 15 minutes. There is no way you can fly between San Francisco and New York in less than two hours, and the reason the Singapore Airlines flight is able to “shrink” the distance is down to great circle routes.