[emmelaich]

But not "non human-powered" flight? If Icarus flapped a little, that counts.

[Retric]

If you can’t maintain altitude without losing significant airspeed, you’re just falling.

[behehebd]

Even if you maintain both you can still be falling (orbits!)

[Retric]

Gravitational orbits lose energy over time. Not really relevant on human timescales but interesting trivia if nothing else.

[behehebd]

Due to friction? Or is it other physics?

[Retric]

Gravitational waves, though in the vast majority of case they are extremely weak.

https://en.wikipedia.org/wiki/Gravitational_wave