[Zufriedenheit]

Can this become dangerous for airplanes? Or are they fully burned up before reaching that low altitude?

[naberhausj]

This article [1] indicates that they burn up at altitudes between 37-50 miles above the surface. If so, that's well above the 40,000' that planes normally fly.

[1] https://www.space.com/spacex-starlink-reentry-pollution-dama...

[Rebelgecko]

There's typically only a small amount of matter that makes it down intact, and they usually aim to deorbit in the middle of nowhere (eg Point Nemo)