At any one time, there are a million people flying above our heads. But what does it take to run this ‘city’$2 30,000 feet up in the sky? This fascinating series explores the hidden world of aviation, revealing the inner workings of the airports, factories and facilities that collectively keep this vast global network functioning. Delving into the science and engineering underpinning the aviation industry, the series introduces the people who keep the whole thing up and running as well as the hidden networks that air travel depends on. Filmed at some of the biggest, busiest, coldest and most remote airports in the world, City in the Sky builds a unique picture of the globally connected system that has transformed the way we live in the 21st century. And with air-passenger numbers predicted to double in the next 20 years, it also looks at what the industry will have to do to keep up.