The third episode of the series looking behind the scenes at Heathrow Airport, revealing the people, systems and science that keep us flying. Dan Snow is at the heart of the airport in air traffic control, and the programme follows all the preparations that ready a long-haul flight for take-off. Dallas Campbell is in Heathrow's paint bay, finding out about the hundreds of markings that must be painstakingly painted on to every plane. And Anita Rani discovers that as you fly off on holiday, you could be sitting above anything from mango to mail, cars to cougars.