[dorfsmay]

What create the air pressure in an airplane? Is it external air speed? Or compression from the engines?

If the latter, how does it work on airplanes with needless engines?

[dschuler]

I don't know much about it, but I think it's usually provided by pressurized bleed air from the engines.

There are cabin pressurization test carts for use on the ground, as well as start carts to provide bleed air for starting engines, and bleed air in turn can supply cabin pressurization in flight, although this probably requires some rigging on the ground.

Interestingly, they switched to electric compressors for the 787 [0] because those no longer provide bleed air from/to each engine to simplify the plumbing.

[0] https://aerosavvy.com/aircraft-pressurization/