London, England (CNN) — As they stare out of the four-story plate glass windows of Heathrow's control tower, Jason Cooper and his team should be gnawing their fingernails and swabbing the sweat from their brows.
On any given day, they're in control of one of the most insanely busy stretches of airport runway on the planet, guiding tens of thousands of people on and off the ground.
One false move could spell disaster: at best the costly loss of a precious runway slot; at worst a genuine aviation tragedy and massive disruption across European airspace.
Which is why it's both surprising and reassuring to find, during a recent CNN visit, that the atmosphere inside the tower at Heathrow, the UK's largest airport, is one of almost Zen-like calm.
"There's pressure, but no stress," says Cooper, who manages Red Watch, one of three groups of air traffic controllers (ATCs) that staff Heathrow's tower day and night. "I think most of us enjoy the pressure."
Under his command today are an apparently genial mixture of men and women of varying ages, all dressed down.
They do their jobs quietly and efficiently, talking into radio headsets, occasionally chatting to one another.
Outside though, the activity is relentless.
High wire balancing act
Heathrow control tower stands 87 meters over the airport.
With five terminals and only two runways -- each handling 19 million more passengers annually than any other airport in the world -- Heathrow is perpetually congested.
Airliners, including giant Airbus A380s, line up on taxiways for takeoff, while the sky is filled with an endless parade of jets coming in from or heading out to destinations around the globe.
It's the job of the tower controllers to keep snarl-ups to a minimum -- a high wire balancing act that requires intense focus and an impressive array of gadgetry.
Standing 87 meters over Heathrow, the tower offers impressive views stretching miles over flat terrain. Even on the cloudy day of CNN's visit it's possible to pick out the tower blocks of London's financial district, nearly 30 kilometers to the east, and Windsor Castle to the west.
That incredible view -- what Cooper calls "the greatest office window" in the region -- is an essential part of the job. The controllers need visual confirmation of every takeoff and landing, only resorting to radar, radio and computers when the weather closes in.
Inside the tower there are two tiers -- a raised central dais where two north and south runway controllers sit back-to-back, and a lower ring occupied by the ground controllers who govern aircraft from start-up at the stand until they've taxied into position on the runway and vice versa.
By law the controllers can only work in 90-minute stretches punctuated by half-hour breaks over a six to nine-hour shift. These relatively short work stints help them focus on the task of moving as many planes as quickly as possible -- up to 42 takeoffs per hour on a good day.
Movement of planes on and off the ground is tracked using computerized strips containing flight data.
Fingers dance over the touch screens as the controllers move around computerized strips (these used to be paper strips) that represent the planes and talk to pilots via the radio.
There's tricky mental juggling to perform as they figure out how to maximize takeoff slots so larger planes aren't followed by smaller aircraft that must wait longer for turbulence to clear.
At night there are extra complications guiding aircraft along Heathrow's busy taxiways. This is done using a giant touch screen that ATCs swipe to illuminate different stretches of Tarmac -- possibly one of the world's largest lighting control decks.
There are also tracking monitors that show the position and movement of all aircraft on the ground, and screens detailing meteorological elements such as wind direction and speed.
Cooper shows off a relatively new piece of kit called the TBS -- or time-based separation -- that's proving crucial to Heathrow's traffic flow. Instead of spacing aircraft on approach by distance, it factors in wind speed and works out how many minutes apart they can land safely.
All good when everything runs smoothly, but what happens when it doesn't?
Much of the control tower's calm atmosphere seems to be down to the contingency measures in place for when problems arise.
It's typically overstaffed in case sudden sickness depletes numbers.
And, says Cooper, almost every system is backed up at least two or three times.
Everything from the phones to the power supply is backed up two or three times in the tower.
In the event of a power cut, the tower has an emergency generator. If that fails there are batteries. And if those go, staff can quickly relocate to a standby tower facility in a secret location nearby.
The controllers really earn their money (in the UK more than $150,000 per year including overtime for senior ATCs) when disaster strikes and their cool nerves are tested to the limit.
Touch screen telephones in the control tower feature an oversized "crash" button, which instantly puts the ATCs in immediate contact with the emergency services and ground crews they need to coordinate with during major incidents.
"It was a very intense day at the office," he says. "Most days here are hard work, some are harder than others. You don't get a job as a Heathrow controller and expect to put your feet up for a couple of hours."
Few people, it seems, are cut out for air traffic controlling.
The qualifications required are minimal, but ATCs need an innate range of skills that allow them to perform the mental acrobatics needed to keep everything flowing. (Try these games on the NATS website: http://bit.ly/1GyKaTa)
Only one in every 300 applicants makes the cut but they come from all walks of life. Cooper says Heathrow employs ATCs in their 20s barely out of school alongside staff with multiple doctorates to their name.
The training is necessarily lengthy, taking up to two years.
Even when qualified, ATCs can spend 18 months working under guidance before being allowed to operate solo. The same goes for experienced controllers moving to a new airport.
And it never stops.
Coolest 'Xbox' ever
Heathrow's control tower simulator is equipped with all the same gadgets as the real thing.
Cooper takes us to a non-descript office block a few miles away from Heathrow where an almost full-sized control tower simulator has been constructed to help train and prepare ATCs and allow them to road test new aircraft and airport structural changes.
It's like a gigantic, awesome $2 million Xbox console with a 360-degree screen.
"We use it to put our ATCs in nasty situations," says Cooper, his fingers instinctively tapping the screen to line computer-generated aircraft up on the runway. "But it has to be relevant, you can't just come in here and set everything on fire just for the hell of it."
Sim manager Daniel Johnson puts his virtual tower through its paces, showing us weather conditions from thick fog to driving snow. He then takes us on a weird, stomach-flipping, out-of-body experience, sending the tower whizzing through the airport and out over London.
We also get to try our hand at clearing a few virtual jets for take off.
Even though it's not real, talking to the pretend pilot (actually Johnson in the next room) and moving the aircraft strips on the computer to get a pixilated Virgin Atlantic 787 off the ground proves a nerve-fraying experience.
Cooper isn't too impressed with the yawning gaps we allow between take offs, but offers some consolation.
"Even for us every day is a school day, you learn something about how to do the job differently.
"The place changes every day and you have to stay on top of the changes, but I cannot imagine having a job where you didn't."