alice writes:

MX, common misconception here about airliners.

Hardly a misconception. The "sweet spot" for airliners is quite high,
and airlines like to be there in order to use the smallest amount of
fuel for a given distance.

You need to look at the fuel required to maintain a given level
of thrust at altitude for a jet engine.

I've looked that the fuel required to cover a given amount of ground,
and it's much lower at high altitudes.

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