[tropo]

No, but cost probably does. There have been a number of satellites flown (GOCE, GRACE, SLATS) with the sort of equipment you'd need. With that equipment, simply measure the strength of gravity in multiple parts of the plane. This gets you altitude, just as GPS or air pressure would, and then you can determine the angle of the plane.

An edit as response to the followup mentioning Einstein, due to HN throttle:

Yes, yes... and it doesn't matter for this purpose, because you can measure gravity at multiple points within the aircraft and because gravity falls off with distance.

https://en.wikipedia.org/wiki/Inverse-square_law#Gravitation

We have built equipment sensitive enough to measure this difference and we have flown it in satellites.

[mannykannot]

"Einstein’s ground-breaking realization (which he called “the happiest thought of my life”) was that gravity is in reality not a force at all, but is indistinguishable from, and in fact the same thing as, acceleration, an idea he called the “principle of equivalence”.

https://www.physicsoftheuniverse.com/topics_relativity_gravi...