A look at the hidden world of the skies above us and the stories of the people who spend their life in flight. The job with the highest pressure at NATS is keeping everyone safe entering or leaving London's airspace, one of the busiest patches of sky in the world. Up to 4,000 people can be in the hands of just one controller at any one time. Tom and Tim, two of the thousands who aspire to be the next generation of air traffic controllers, are beginning the rigorous three-year course. For some, the growth in air traffic is too much. Martin Barraud is leading a campaign to stop the narrowing of flight paths and increased noise overhead. Protest group Plane Stupid use direct action to raise awareness of the environmental cost of flying but face a possible jail sentence for taking part in a sit in.