The urban marvels of London's Canary Wharf and the O2 Arena are enveloped in white. The usual buzz of activity at London City Airport's 80-foot-high control tower is quiet. The scores of screens include a feed of codified wind speed, temperature, visibility and trackings of the aircraft in the London area.

"Yesterday, the fog cleared within 10 minutes and we were up and running again," says senior controller Richard Crawley.

One of the perils of being situated next to the Thames is that the fog hangs around longer. Better days see around 36 in- and outbound flights an hour. "Once you're plugged into the system, it is always high pressure," Crawley says, because at any moment "a pilot can declare mayday and you've got to kick into action."

Crawley, 33, has always been part of the airport scene. Before talking planes up and down safely, he was a flight dispatcher in charge of turnarounds. "I worked at Manchester airport for six years, making sure all the services turned up and got off the planes in time, ready for the next flight," he says.

A year-long adventure in Australia and New Zealand and a bored Sunday internet surf later, Crawley applied on a whim to become an air traffic controller through the UK's National Air Traffic Services.

"The selection process is quite rigorous. You're given a lot of 3D problem-solving scenarios to test your analytical skills," he recalls.

There is a misconception that maths is a staple feature in an air traffic controller's life, but only light calculations are involved, Crawley adds.

After three months basic training with textbook learning and written exams, students are placed into one of three operational disciplines: area, approach or aerodrome (tower).

Crawley followed the path of an aerodrome controller and was soon moving heavy traffic in a simulator. After finishing his paid training, he was posted to a unit to start his on-the-job training.

"When you bring a plane in for the first time on your own, it's quite a strange moment," he says. "You've been used to having someone with another headset listening to what you're doing and then you think, 'Wow, I'm really doing this now'."

Air traffic controllers do not hand out directions to pilots; that's the job of the instrument landing system or the radar controllers. What they do is use a coded language to clear aircraft to land and take off.

"We issue a clearance and a squawk [a four-digit code punched into a piece of kit on the aircraft], and give an aircraft clearance to start, then we'll taxi them, clear them for take off, and two miles [about 3.2 km] out, we pass them on to radar control," Crawley says.

"For an inbound flight, communication starts when the aircraft is up to five miles away from the airfield. From that point, it takes several minutes until it is on the ground. You need the mental capacity to focus on several aircraft at once, which is why you're only allowed to be plugged in for up to two hours before taking a mandatory half-hour break."

The view from the tower gives instant gratification. "I love seeing what I'm doing. It's a thrill, especially after a busy session," Crawley says.

The opening ceremony of London's Olympics in 2012 was just that and more. "We had been building up to it for two years. On the day, there was a 15-minute shutdown of the airfield to allow the Red Arrows [Royal Air Force aerobatic team] to fly over. We are only three miles from the stadium, so all eyes were on us to get it right. We were talking to police, military and filming helicopters, as well as taking care of the flights coming in and out of the airport. It was one of the most satisfying feelings when we finished for the night," Crawley says.

An air traffic controller is somewhat of a choreographer. All the movement on the airfield is carefully timed. As passengers, seeing planes queue jump is irritating, but the controllers are only quickening the process of getting you to the skies: "The time of departure on a passenger's ticket doesn't mean anything up in the tower. It's not a first-come, first-served basis."

The departure sequence is decided according to the aircraft's route and weight vortex. A bigger aircraft creates a bigger vortex of air behind it, and there are five vortex categories.

"An A380 is known as super; 747 is heavy and medium; small and light follow. Between a heavy and a light, you have to give two minutes. If you switch it the other way round - putting a light first then a heavy - you can have one minute between them. It's the most productive use of time."

In an emergency, air traffic controllers orchestrate everything. "A few years back, an aircraft's nose wheel collapsed, which caused it to skid as it landed. We had a string of aircraft behind it and others waiting to depart, so we got into gear and called up the fire services and the airport switchboard, who then cascaded on to other services. There are only four of us in the tower, so you have to be able to work in a team." Guardian News & Media