It is remarkably hard to tell especially as your senses get mislead in a plane. This is why there is a very big distinction between VFR and IFR. With VFR (vis

It is remarkably hard to tell especially as your senses get mislead in a plane. This is why there is a very big distinction between VFR and IFR. With VFR (visual) you look out the window and can clearly see the horizon, which way is up etc and cannot fly at night or in weather/visibility conditions. With IFR (instrument) the training is to ignore your senses because they will mislead you and use your instruments instead even if they seem wrong based on your senses. Here for example is a plane rolling while tea is being poured. If you couldn't see out the window you wouldn't even know what was going on http://www.youtube.com/watch?v=Xp2Uc9XvmjY http://www.youtube.com/watch?v=Xp2Uc9XvmjY There have been crashes where VFR pilots have flown into instrument conditions and ask which was is up. It sounds incredulous to us on the ground but it really does happen. The net effect is that the passengers and crew on the plane would not have felt as if anything is wrong.