This episode explores just what it takes to keep the ‘city in the sky’ airborne and safe between take-off and landing. Once you’re in the air, flying may seem everyday and uneventful, but behind the scenes there are thousands of hidden processes keeping you there. One key element of this is navigation, and we discover exactly how pilots find their way across thousands of miles of open sky in the dead of night. We reveal the hidden global network of locators known ‘waypoints’ that pilots can follow through the air. We meet the air traffic controllers responsible for regulating the busiest airspace in the world: the skies over Atlanta, Georgia. On every shift, they hold the lives of thousands of passengers in their hands. We also explore the revolution in aircraft construction, looking at how new ‘composite’ materials have enabled the evolution of planes that are lighter and stronger than ever before. They have also helped transform the passenger experience – thanks to their strengths new planes can be put under high pressure, and this extra air helps us passengers feel better in flight. And it’s not just about the planes themselves, it’s also about us human beings. When we get sick in the air, there’s a hidden airborne medical service available to help. The Medaire facility, in Phoenix Arizona, offers highly trained ER doctors who can remotely diagnose passengers who fall ill at 35,000 feet. The existence of all of these elements have helped make flying safer than ever before.