Perhaps this: >In inverted flight, the curved wing surface becomes the bottom surface, and according to Bernoulli’s theorem, it then generates reduced pressure

Perhaps this: >In inverted flight, the curved wing surface becomes the bottom surface, and according to Bernoulli’s theorem, it then generates reduced pressure below the wing. That lower pressure, added to the force of gravity, should have the overall effect of pulling the plane downward rather than holding it up. This is not what Bournoulli's theorem states. Bournoulli's theorem doesn't say anything as to why fluid flows the way it flows. It just says for a fluid in a steady state flow, increases in speed are associated in decreased pressure. Hence the principle suggests, if you find a plane is able to fly steady upside down, then expect to find the air flowing faster over the wing on the opposite side of gravity under those conditions - just likewise when a plane is normally flying right side up. Again why fluid flows the way it does around airfoils is separate question -and really the crux of the mystery here. Answers to this is probably hidden in the solutions to the Navier–Stokes existence and smoothness problem: https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_existence_and_smoothness https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_existenc...