Not entirely sure if this is a glitch or not, but I’ve only seen it rarely when I’ve switched to viewing a traveling plane in Pocket Planes. Once you view a different screen and go back to the same plane’s view it will be back to normal. But I think it’s not a glitch and rather an Easter egg because when the plane is upside down, the passengers all seem to be screaming, which would be typical when you’re in a plane and upside down.