17 Beware the vortex Pilots often wait a long time to get clearance. This is to allow the air to settle after a previous take-off, as a plane’s wingtips generate vortices in the air, which can take two or three minutes to disperse. If the following aircraft set off immediately, the rapidly moving air would make the plane difficult to handle. The delay gives the air time to recover from the miniature whirlwinds caused by the preceding plane. 18 The doors aren’t locked In practice, the doors on a plane don’t need to be locked. If you watch an aircraft door being opened, it swings in an unusual way. It first has to be opened inwards before manoeuvring it out of the way. Once the plane has taken off, a significant pressure difference soon builds up between the inside of the plane and the outside. This differential forces the door into place. To open it, you would have to pull against the air pressure, well beyond the capabilities of human muscles.