Communication: How Air Traffic Control Works

A brief overview of the air traffic control system, and an explanation of how planes are safely guided from take-off to landing.

You may not pay much attention to it the next time you fly somewhere, but from the moment your airplane door closes, until the moment it opens again at your destination, the timeliness and safety of your journey are ensured by the air traffic control system.

So how does air traffic control actually work, and how does your plane get safely from point A to point B? The system is a complex combination of radar, computers, and radio transmitters. And of course, efficient communication between the pilots in the air and the controllers on the ground is just as important. For this reason, English has become the common language of air traffic control. All passenger and military aircraft flying in the United States are required to present to Central Flow Control (CFC), what is known as a flight plan - basically, a proposed itinerary of exactly how they intend to fly from one airport to another. Although complex, the flight plan is similar to an itinerary you might draw up for a road trip, although this one includes not only direction, but altitude and speed as well. The amount of fuel that will be used is calculated as accurately as possible, too. The plan is then approved and overseen by air traffic control. Keep in mind that at any given time, there are about 4000 airplanes flying in the airspace over the United States - many of these planes are flying into and out of the same airports, or within the crowded airspace above major cities. Not only must each individual aircraft's flight plan be approved, they may need to be modified because of weather or other delaying factors. Air traffic controllers - the people you see on movies who sit in a darkened room hunched over a computer monitor - are also responsible for maintaining a safe distance between planes in the air. Controllers must also direct planes that are coming in to land to a particular point in the sky so they can land at a specific time - these "˜time slots' are especially important at a busy airport such as New York's JFK where planes land every minute or so.

The nerve center of the huge CFC system is based in a huge building in Washington DC, but the system itself is subdivided into smaller and more manageable sections. For example, if you were to fly from New York to Los Angeles, your plane might pass through several air traffic centers, as you crossed the country. Each center is responsible for controlling their own "˜section' of sky, and safely handing the plane over to the controller in the next center. This is even more complex if you are flying overseas - you may pass through the control sector of several countries before reaching your destination. Usually, the buildings that control that particular section of airspace are located in secure facilities far from any airport. The control tower that you see at the airport is mostly just responsible for instructing the pilot which runway to use and when to take off and land. Most aviation accidents happen at take off or landing, so the task of guiding the plane through the maze of taxiways and runways at the airport is just as essential as guiding it while airborne. If you could step inside the main room at the control tower, you would see a huge flat diagram of the airport, with each plane that is currently on the ground portrayed by a different colored marker. These markers are constantly being moved around to depict the exact location on the taxiway or runway of every aircraft. Once airborne, responsibility for the flight's route switches over to air traffic control.

So what actually causes those all too frequent delays? One of the jobs of air traffic controllers is to maintain a safe distance between planes - this may mean "˜juggling' with an aircraft's speed, direction, and rate of climb or descent. All this is being done in a three dimensional section of airspace, and there are usually other airplanes in that section too. At a busy airport, there may be literally more planes trying to take off and/or land than the system can handle safely. Keep in mind that not only must a safe distance between planes be maintained, but also a safe time between take offs and landings. Busy airports can have what is known as "˜holding patterns' i.e. all the planes coming into land will be stacked up one behind the other and may have to circle before being cleared to land. The FAA recently approved a plan by American and United to reduce their daily flights into and out of Chicago's O'Hare airport - one of the world's busiest - in an attempt to help reduce delays. Some airports may have only one runway or weather conditions may require more time between take offs and landings. This may lead to delays, or even cancellations. Sometimes an airline will make the difficult decision to cancel one flight, so that all the other flights that day can depart on time. Weather is a main cause of delays of course, even though the weather problem may not be apparent. For example, fog in San Francisco may cause departures to be spread out more than usual, making your flight arrive late in Dallas, and then be late taking off for New York. CFC forecasts the weather every day and plans accordingly.

As more and more passengers take to the skies, the air traffic control system is constantly trying to strike a balance between safety and efficiency. Not surprisingly the job of an air traffic controller is one of the most stressful jobs there is - your life is literally in their hands. Nobody likes delays when they are flying - but the next time your flight is delayed due to air traffic control, you will have a better idea of why that is.

© High Speed Ventures 2011