How Air Traffic Control Works

​The US airspace is the largest and busiest in the world. It takes 520 air traffic control (ATC) towers and 14,000 air traffic controllers. ATC maintains order on the runways and skies for seamless takeoffs, flights, and landings.

ATC functions like a well-orchestrated opera as airplanes move through different flight phases. It relies on systems and human resources to control airport operations and air traffic flow. Air traffic controllers communicate and coordinate with each other radar through ACT towers, terminal control centers, and radar systems.

The US airspace has 21 zones (centers). Each zone has its sectors and a distinct airspace measuring 50 miles in diameter, called Terminal Radar Approach Control (TRACON). Each TRACON has several airports, each with a distinct airspace. ATC system command center monitors planes as they move through different zones.

In the preflight or the first stage of every flight, the pilot conducts preflight checks and files a flight plan with the ACT. A flight plan captures aircraft particulars, such as the airline name, flight number, type of aircraft, equipment, intended airspeed cruising altitude, and route flight. At the ATC, a flight data person checks the flight plan, reviews it against the weather, and then enters it into the FAA host computer.

The host computer generates a flight progress strip, which contains all the necessary details about a flight and goes from one controller to the next across the flight’s path. Once ATC approves the flight plan and flight, the flight data person clears the pilot and passes the strip to the ground controller, who is responsible for all ground traffic.

When the ground controller ascertains that it’s safe, they direct the pilot to push back the aircraft from the gate. The ground controller uses radar to track all the taxiways, ensuring a pilot doesn't taxi to an active runway. They then direct the pilot on which way to tax and which runway to take off.

The local controller clears pilots to take off. Even with clearance, it’s up to a pilot to decide if it’s safe to take off. As the plane lifts off, the pilot activates a transponder, which relays information on airspeed, flight number, altitude, and destination. At the same time, the local controller hands over the reins to a TRACON-based departure controller. From there, the pilot talks with the departure controller.

The departure controller monitors a flight through TRACON airspace. Once it leaves TRACON airspace, the ARTCC controllers take over. Whenever a plane passes to another controller, the FAA host computer updates the flight strip and sends it to the new controller.

An ARTCC involves at least two center controllers. The radar associate controller reviews the flight strip and coordinates with that sector’s radar controller. The radar controller ensures a safe distance between flights in a sector by specifying cruising speed and altitude. Once the flight leaves a sector, the next sector’s controllers take over.

As the aircraft approaches the destination airport (50 miles), that zone’s TRACON approach controller takes over. They advise the pilot on the approach direction, speed, and altitude. When the plane is within 10 miles of the runway, the local controller at the airport takes over. Once the pilot has landed, the ground controller takes over and directs the pilot to the right terminal gate.

Passing planes from sector to sector and center to center helps ease air traffic. The alternative would be for just the departure and arrival ATC to coordinate flights, which would lead to collisions on the runway and in mid-air.

Douglas Charney

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