If you’ve ever looked at the world map on Flight Radar 24, you’re bound to wonder how all the aircraft in the skies at any given time manage to avoid one another while traveling at nearly 600 miles per hour in almost every conceivable direction five miles above the surface of the Earth. At any given time, there are between 8,000 and 13,000 airplanes in the air. Over 30,000 flights with two million passengers on board take off every single day in the US alone. Air traffic control (ATC) is responsible for bringing order to what would be a dangerous and chaotic situation and we owe our thanks to the dedicated men and women whose job it is to keep us all safe.
Different regions have different names for the departments involved in these exacting air operations. In the United States, airspace is divided into 21 separate zones and each is further split into different sectors. There are pockets of airspace in each zone that have a diameter of approximately 50 miles. The US Federal Aviation Administration (FAA) has formed the nation’s air traffic control system around these divisions and there are controllers assigned to specific zones. Terminal Control Centers (TRACONS) are responsible for providing all ATC services within their airspace. Generally, there are four types of traffic flows for which Terminal Control Center controllers are responsible. These are departures, arrivals, overflights, and aircraft operating under Visual Flight Rules (VFR).
Prior to takeoff, pilots entering the system for instrument flight must submit a flight plan to ATC and must wait for a response to their request. ATC will either approve the plan as submitted (cleared as filed) or may change it, but in either case, pilots must read it back to ensure it’s been interpreted correctly. (I can recall filing many instrument flight plans with ATC and was always glad I kept a lap pad and pen handy to jot down their instructions as controllers invariably speak rapidly.) Once clearance is received, the pilots in command of the aircraft will be in communication with local controllers in the tower who will provide taxi instructions and give permission for take off. Once airborne, a different controller will track the aircraft’s progress through the airways. Each controller is responsible for aircraft in a certain airspace. When the aircraft is nearing the edge of their sector, they coordinate its handover to the next controller. This continues throughout the plane's journey until it reaches the destination airport.
How do controllers know where an aircraft is at any given time? An avionic instrument called a transponder combines the ability to transmit information and to respond to an inquiry from ATC radar sites. Much of this communication is automated. A pilot is told by ATC to insert a specific code into the airplane’s transponder before flight (squawk a 4-digit numerical sequence which is distinct for that aircraft and that flight). There are some 4,096 different combinations of these four digits. The pilot determines which four-digit code to insert based on either the code that ATC has assigned or, if flying under Visual Flight Rules, he or she will use the standard code of 1200. There are a handful of emergency transponder codes as well. Code 7500 is the designator for hijacking, 7600 is used for lost communications (complete radio failures), and 7700 is the catch-all code for other emergencies. I should point our that aviators almost never use the word, ‘code.’ Instead, the four digits of coded signal is referred to as a “squawk.” Indeed, the word, “squawk” is both a noun and a verb. For example, let's assume you're flying in a Cherokee and your call sign (aircraft registration number) is abbreviated as 62V. Should ATC decide that you should change your current transponder code to 2641, this is what you’d hear over the radio: Cherokee 6-2-Victor, squawk 2-6-4-1.
In the United States, air traffic controllers go through two phases of training. The first phase is typically completed through a program approved by FAA Air Traffic Collegiate Training. Thirty-six schools across the country are approved through this initiative to offer associate, bachelor’s, and master’s degree programs for prospective air traffic controllers. Those interested must be US citizens, be younger than 31 years of age when they are first hired, and pass a criminal history background check as well as a medical exam that includes vision, color vision, hearing, psychological, substance abuse, cardiovascular, and neurological screenings. Graduates of approved programs must receive a recommendation from their school and pass the FAA’s bio-data assessment and Air Traffic Skills Assessment Test to move on to the next step in the training process. Based on the results of these tests, the FAA hires a group of graduates to continue their training at the FAA Academy. Here, air traffic controllers receive intensive training that includes classroom instruction and work on air traffic control simulators. Students who complete this training program are assigned to a job location where they continue their training while working. Air traffic controllers must be certified by the FAA.They earn certification by passing a knowledge and practical exam and meeting experience requirements through on-the-job training after graduation from the academy.
During instrument flight, every factor is decided beforehand from the approved flight plan to the departure runway assigned, particularly when it comes to commercial flights. Air Traffic Control ensures that pilots adhere to the plan and will be in contact should an aircraft veer off the approved route. The ultimate purpose is to avoid collision and ensure a smooth flow of air traffic for a safe and seamless journey. You’ll note that airport traffic control towers are very high structures so that controllers have an optimal view of the airport environment. The control tower is an essential element of aeronautical operations. At controlled fields, no aircraft is permitted to fly without being in communication with the tower and control centers are responsible for organizing air traffic so that take offs, en route flight and landings occur without incident. Today, there are Web sites that share control tower live signals at many of the world’s busiest airfields so that users can listen to pilot and controller communications in real time.
The importance of air traffic control cannot be overstated. We have controllers to thank for managing the flow of air traffic, ensuring that aircraft maintain a safe distance from one another and follow designated flight paths. They monitor weather conditions and adjust flight routes accordingly, as well as provide pilots with critical information about other aircraft in the area. Without air traffic control, the aviation industry would be unsafe and chaotic. The role of ATC has become even more critical in recent years, with the increased growth of air travel since the pandemic which has placed further demands on the airspace system. As the number of flights continues to rise, air traffic controllers must work even harder to ensure that each flight proceeds in a safe and secure manner.
Until next time...safe travels.
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