If the sky at the top of Mt Everest is black due to lack of atmosphere ....?

Question

then why the heck isnt the sky black when you are in a plane?

Answer 1

Because the sky is upside down when you are in a plane.

The sky at Mt. Everest is only black at night. Just like everywhere else.

Answer 2

The sky is not black at the top of Mt.  Everest.  All you have to do is to look at the TV specials.

Answer 3

It's not.