[reaperducer]

By default, flights are optimized for cost.

Decades ago, before all of the routes and scheduling got to be more of a mesh than an ideal hub-and-spoke, this was an absolute. But now, being late can cost far more money than what would be spent in fuel.

Now, very often the airlines would rather burn some fuel and keep a plane on time than delay or cancel a dozen connecting flights at the destination.

[SEJeff]

I was noting the fact that they are able to change the speed of a plane to optimize for the specific key performance indicator they deem the most necessary at the time.

I used to work in IT for delta a touch over a decade ago as a systems engineer.

[fomine3]

Optimize for fuel cost means that planes usually don't fly at maximum speed. It also provides margin to avoid being late by speed up.

[SEJeff]

Precisely!