Airport control towers house the workers and much of the technology underpinning modern aviation. In the U.S., the Federal Aviation Administration owns, builds and operates most control towers and provides air-traffic-control services at 264 airports.

In contrast, air-traffic control in some countries is privatized. For example, Nav Canada, a private non-profit corporation, has been responsible for air traffic control since 1996 in Canada, and other countries in which private air-navigation-service companies operate include Germany, Italy, Switzerland, Norway, Poland, the Ukraine and Indonesia.

Air-navigation technology in the coming years will undergo a major transformation. Since the World War II era, according to the FAA, "the thousands of planes overhead at any given time are flying indirect routes over radar towers. The next-gen system that is being introduced is an upgrade to satellite-based technology. Satellite navigation will let pilots know the precise locations of other airplanes around them. This will allow more planes in the sky while enhancing safety, and satellite landing procedures will let pilots arrive at airports more predictably and more efficiently."

According to Quentin Browell, the head of communications for the Civil Air Navigation Services Organisation (CANSO), "Automation will be the big technological game-changer in the next few years. Aircraft have gone through several automation cycles over the past 30 years, but air traffic management [ATM] is now only really starting that journey. We will see more machine-to-machine interaction, enabling us to fly planes closer together and thus build capacity," that is, allowing more aircraft to take off and land within a given time period.

Commercial aviation is expected to grow steadily. "We forecast an average annual global growth rate of air-passenger traffic of 4% for almost two decades," says Angela Gittens, director general of Airports Council International.

Several very tall towers are being developed. Most notably, a new 136-meter-high control tower under construction at King Abdulaziz International Airport (KAIA) in Jeddah, Saudi Arabia, will claim the record for the world's tallest tower when it is completed next year.

KAIA handles the enormous number of pilgrims visiting the holy cities of Mecca and Medina. The first phase of a three-phase expansion will increase the airport's capacity to 30 million from 16 million when it is completed later this year.

A new control tower currently is being built at the Indira Gandhi International Airport in New Delhi by the private airport operator Delhi International Airport Ltd. The 102-m-tall tower will accommodate 21 controller positions within the visual control room and 12 ground controller positions.

While almost all airport control towers are free-standing, a few have been sited on existing buildings. The highest such tower is Canada's Vancouver Harbour Control Tower, at 142 m, which manages seaplane traffic using the Vancouver Harbour Water Airport. It was built on top of a 29-story office building and is considered the 31st story because of a small base it sits on.