A spirit level does not work in an accelerating frame of reference. From the point of view of a spirit level, there is no difference between straight and level flight (1g due to earth's gravity) or a spiral dive (>1g due to a spiraling turn downwards).

Gyroscopes work, which is why artificial horizons are a thing. But an artificial horizon doesn't show anything except where your nose is pointing. You need all sorts of other sensors to tell you which direction you are actually going.

OK, thanks for the succinct explanation. Its nice to know that people smarter than me are trying to solve this.

Not smarter, just an aviation layman geek :)

A spirit level does not tell you anything. The had existed in planes almost since planes exist.

You can not differentiate a force coming from plane acceleration and deceleration from gravity(which also comes from some kind of apparent deceleration). People in the space Station are being affected almost with the same gravity that you or me.

In fact, a spirit level or your ears provide you with wrong information all the time with no visibility.

With planes, the first thing you have to learn is not trusting your senses.