The world's first air traffic control tower was commissioned by the UK Government 100 years ago.
It was built at the now-closed Croydon Airport, south London, and stimulated the development of air traffic control.
Due to the rise of airline passenger services, on February 25 1920 the Air Ministry ordered the construction of a building that was 15 feet tall, with large windows on all sides, to control air traffic.
The Aerodrome Control Tower was completed later that year and provided a name and design that has remained synonymous with air traffic control. It was rebuilt in 1928 and converted into a museum in 2000, following the closure of the airport in 1959.
The first controllers provided basic traffic, location and weather information to pilots over the radio, and the progress of about a dozen daily flights were tracked using basic radio-based navigation and plotted on paper maps.
Today, UK air traffic control provider Nats handles up to 8,000 flights a day in some of the world's busiest airspace.
The aviation industry wants the use of airspace to be made more efficient. Many of the flight paths used by airlines are more than 50 years old, which has been compared with driving across the UK without using a motorway.
The Department for Transport is working with the Civil Aviation Authority on plans to modernise airspace.