So you're flying from, say, London to China, and you take a flight. Suddenly, you find yourself needing to daven. So you're shuckling, saying psalms, or whatever and then suddenly, out of the blue, the pilot says, "We have just passed Jerusalem. The city is behind us."
What do you do? You're supposed to face towards Jerusalem, but you're in the middle of the amida or some other important prayer that shall not be interrupted. Do you turn around? Do you keep facing East?
Assume you are standing while the plane is flying.