Air traffic control towers (ATC) are now among the most distinctive and easily recognisable buildings at airports with each gateway seemingly boasting its own unique facility.
Like modern day lighthouses they are often imposing structures that tower into the heavens and can be seen from miles around.
They continue to get bigger, better and taller and, after being around for the best part of a century, are now considered part of the furniture at airports.
But the fact is that most airports don't have them at all. These are the small-to-medium sized airports, which simply don't generate enough traffic to justify the significant investment required to build them.
And when flight movements do suddenly soar – for example, at an annual one-off event such as an air show – airport operators have the option of erecting temporary towers to handle the extra demand.
These are also used when natural disasters strike. The Federal Aviation Administration (FAA) recently dispatched a portable control tower to Haiti to assist with aircraft operations at Port-au-Prince when the permanent building was debilitated by the devastating earthquake of January 12.
The temporary tower – 44ft long, 13ft high, 8ft wide and weighing about 25,000 pounds – was transported aboard a large, chartered cargo aircraft, accompanied by two diesel-powered generators and supporting fuel tanks. FAA technicians made it operational within 48 hours of its arrival at Toussaint Louverture International Airport.
Temporary towers can be indispensable, but for the world's busiest gateways, control towers are, of course, both permanent and essential. They're manned 24 hours-a-day, all year round by a team of controllers who have undergone rigorous training to operate the sophisticated equipment installed in today's most modern structures.
That equipment varies according to local needs, but on top of basic radio and telephone systems this would generally include computerised flight progress monitors, a radar display showing traffic on the aerodrome, aviation light signals in the event of radio failure, and wind and pressure gauges.
A rotating beacon helps pinpoint an airport's position at night, using colour-coded flashes to inform incoming pilots if it is a civil or military airport, whether or not it is used by the emergency services, and to warn them if it is close to water.
Windows giving 360-degree field of vision are generally tilted outwards at a 15-degree angle to eliminate reflection of controllers' equipment and cut out glare, while ceilings are often painted black. In an environment where visibility is so important, many companies produce specialist materials to aid the work of the air traffic controller.
A company called Plastic-View, for example, claims to have installed its product in 98% of all US control towers, and in 75 countries worldwide. Its ‘see-through’ window shades dramatically reduce sun glare, while preserving a clear view, allowing air traffic controllers to maintain visual contact with both air and ground traffic, and eliminating eye-straining glare.
It also makes computer and radar screens easier to view, and because the materials reflect over 60% of the total solar energy, temperatures are kept uniform throughout the tower, making the working environment far more comfortable.
Today's towers represent considerable feats on many levels: architecture, engineering, computer systems and assembly.
When the top 27 metre portion of London Heathrow's €60 million tower – a heavyweight structure tipping the scales at 900 tonnes – was moved to its new location near Terminal 3, three 144-wheel remotecontrolled hydraulic flatbed trucks were required to transport it from the construction site.
Designed by the Richard Rodgers Partnership, the 87 metre high tower is twice the size of its predecessor and is easily one of the most distinctive new additions to London’s skyline in the past five years.
It's all a far cry from the earliest days of air traffic control, when controllers would stand on the airfield and communicate with the pilots of incoming flights using a system of coloured flags.
It was not until 1930 that the first purpose-built control tower was erected at Cleveland's Hopkins International Airport, becoming fully operational five years later. And, 1935 heralded the world’s first ATC centre in New Jersey, which co-ordinated aircraft movements between Newark, Chicago and Cleveland.
Early controllers tracked aircraft using blackboards, maps and boatshaped weights to perform the most basic form of air traffic control. This extraordinarily simple system however, was revolutionised soon after World War 2 by the advent of radar, which by 1952 was being used by civil aviation authorities to control both approaching and departing flights.
Twelve years later came the introduction of two ‘flight separation’ layers, one governing aircraft flying at 1,000-18,000ft, and the other for flights cruising at 18,000-45,000ft.
The distinction of being the world's tallest tower (142 metres) is claimed by Vancouver Harbour Water Airport or Vancouver Coal Harbour Seaplane Base as it is also known, although this claim is slightly unfair as it is perched on top of a skyscraper!
In reality though the record belongs to Bangkok–Suvarnabhumi and its 132.2 metre high ATC tower, although it officially only holds the honour of possessing the tallest free standing tower.
Height-wise, it may be one of the more modest at 51 metres, but Sydney Airport’s ultra-modern tower is certainly one of the more striking, featuring a central support column, passenger lift and a spiral emergency staircase.
The designers were briefed to come up with a design that was not only functional, but in time would evolve into a popular and distinctive Sydney landmark, and arguably they have been successful, although understandably it cannot quite compete with the city's famous opera house when it comes to grabbing tourist attention.
The ATC tower, the airport’s fifth since its 1937, was also one of the first to use sophisticated touch-screen consoles to give controllers easy access to radar, communication and meteorological data.
Another gateway looking to make a big impression with its control tower is Abu Dhabi International Airport, which plans to open a new 109 metre high facility later this year as part of its ongoing $6.8 billion development programme.
The eye-catching curved design of the 20-storey tower, together with its location between the airport’s two runways, ensures that few passengers will be able to miss the new $40 million addition to the airport’s infrastructure.
And Cleveland Hopkins, which claims to have been the first airport in the world to open an ATC tower, will soon boast one of the newest if its planned new 300ft tower opens in 2012 as scheduled. The facility will replace a 21-year-old building that in 1999 leaked so badly that it was shut down for a day because of safety fears. The existing ATC tower houses two separate air traffic control operations and 66 controllers.
According to FAA spokesman, Tony Molinaro, Cleveland's new tower “will be an integral part of the Ohio airport's expansion programme and part of a wider FAA effort to replace ATC towers in dozens of airports across the United States.”
Control towers are absolutely integral to flight safety, so it may come as little surprise to learn that in the US the FAA runs a National Air Traffic Control Tower of the Year award based on management, facilities and performance statistics.
Equally unsurprising is the fact that control towers have become a prime target for political activists. In November 2008, anti-government protesters allied to the People's Alliance for Democracy stormed the control tower at Bangkok–Suvarnabhumi,
Thailand’s main international gateway, just one day after invading the main terminal and forcing several airlines to cancel flights.
The erection of a new ATC tower generally reflects the need to update technology and, where required, accommodate extra staff to handle rising levels of air traffic. But even when control towers have outlived their operational usefulness, they're not necessarily bulldozed.
Manchester Airport's five-storey hexagonal tower was decommissioned following a €56 million revamp of Terminal 1, but the airport has unveiled plans to convert it into a trendy bar, giving up to 100 customers a panoramic view of the airfield.
When it comes to accommodating flights, there is little doubt that the air traffic controllers at Hartsfield-Jackson Atlanta, Chicago O’Hare and Dallas/Fort Worth are the busiest in world, with Atlanta alone handling more than 2,500 flights daily.
However, for one week every year, they have a rival in tiny Wittmann Regional Airport in Oshkosh, Wisconsin, when aviation enthusiasts from across the planet descend upon it for the Experimental Aircraft Association's annual AirVenture.
The week long aviation show attracts some 10,000 flights and such is the enormity of the event that it is known as the Super Bowl of air traffic control, where only the best controllers are on duty. And, on a single day in July, 2008, they handled 3,035 flights in just 10 hours – 400 more than Atlanta did on the same day.
What its controllers wouldn’t give for a state-of-the-art ATC tower like the one in Atlanta or planned for Abu Dhabi or Cleveland Hopkins.