How are planes tracked as they fly around the world?

This month marks the ninth anniversary of the tragic and mysterious disappearance of MH370 — a Boeing 777 that flew between Kuala Lumpur, Malaysia and Beijing on March 8, 2014. So far, there is no explanation. no certainty about what happened to the plane.

The event was shrouded in confusion and controversy. How a multi-million dollar machine with all its passengers and crew could disappear into thin air is the most baffling element of the story.

It is commonly believed that every plane appears as a small blip on the screen of the air traffic controller. You may have seen a movie where that blip disappeared spectacularly, causing disaster for the aircraft involved.

However, it may come as a surprise that aircraft are not always as visible to air traffic control as that little blip. In some parts of the world, air traffic control does not have equipment to detect aircraft and, therefore, does not have a screen to display them.

That said, no matter what facilities are available for air traffic control, there is always some layer of safety procedures in place to ensure that planes are safely separated from each other. In fact, the aftermath of the disappearance of MH370 has caused the global civil aviation authority to change the way it tracks planes.

flight MH370

Air traffic control tower at the airport. RAFAEL CORDERO/GETTY PICTURE

At dawn on March 8, 2014, flight MH370, a Boeing 777-200, took off from Kuala Lumpur International Airport (KUL) for a scheduled flight to Beijing. After climbing to 35,000 feet and approaching the edge of Malaysian airspace, the crew was instructed to contact Vietnamese air traffic control at 1:19 a.m. Malaysian time.

To do this, air traffic control gives the pilot a new radio frequency that they repeat to confirm that they have understood it correctly. Here’s what they did. It was then standard procedure for pilots to change radio stations from a Malaysian frequency to a new Vietnamese frequency and contact Vietnamese air traffic control. However, that radio call was never made on the new frequency.

Three minutes later, at 1:22 a.m., the flight disappeared from the screens of air traffic control and was heard from no one.

radar control

The most common way that air traffic control tracks aircraft is by radar. The system’s origins date back to World War II when British scientists developed technology to detect German aircraft flying over the UK mainland.

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Primary surveillance radar

The simple form of radar developed by the British is now known as the main surveillance radar. It uses a beam of electromagnetic wave energy sent into the sky by a transmitter.

As this wave travels out into space, anything it can hit (such as an airplane) acts as a deflector. This causes some of the waves to bounce back to the ground, where a signal is received by a station. The return of this radar is then displayed on the screen to the radar operator, who can determine the relative distance and direction of the aircraft.

The radar system uses electromagnetic waves to detect aircraft. RBKOMAR/GETTY PICTURE

Using multiple stations, it is eventually possible to superimpose the signals and find out the approximate altitude of the aircraft.

However, this system has limitations in both range and accuracy. The radar signal will generate a return if it hits anything — including thunderstorms, hills, and even small objects like birds. As a result, it is often difficult for radar operators to be sure of exactly what the return indicates.

This was fine in the early days of commercial aviation. However, as the skies get busier and the airspace more congested, air traffic controllers need a better, more accurate way of tracking aircraft to ensure flight safety.

Secondary surveillance radar

To address the growing challenges of using the original radar system in busier airspace, a new system called secondary surveillance radar was developed. Instead of sending signals from the ground and relying on that to attack the aircraft, the system uses an interrogation station and an on-board device called a transponder.

Before departure, pilots receive a specific four-digit number to enter into their transponder, identifying that aircraft for air traffic control. This is called the squawk code. The interrogation station can then send a signal to the specific aircraft, requesting certain information. When the transponder receives these requests, it sends back an encrypted signal containing the requested information.

The transponder can operate in two modes. Mode C returns the aircraft’s position, squawk code, and altitude up to 100 feet. In addition to position and squawk codes, Mode S sends altitude accurate to 25 feet, as well as aircraft call signals (e.g. “United 26LP”), magnetic heading, specified airspeed, ground speed and speed of rotation. It also tells the controller how high the pilots have directed the plane to ascend or descend.

All this extra information allows air traffic control to know exactly what the plane is doing without spending time asking the pilot. It is especially useful to operators who sequence the aircraft on final approach to the runway because it allows them to ensure that one aircraft does not overtake the aircraft in front. Also, since the controller can know the altitude the pilot has set for autopilot, air traffic control can detect any errors before they become a major threat.

However, a major weakness of secondary surveillance radar is that it still requires a ground-based radar system to detect the aircraft’s position. This is fine on land, where there are many radar stations, but as soon as the plane flies over large areas of rainforest, desert or water, the plane can no longer be tracked.

A good example of this is over the Atlantic Ocean. On either side of the pond, which is part of Canada and Ireland/Scotland air traffic control, good radar coverage allows for precise radar positioning. However, as the aircraft flew further from land, the radar could no longer detect them. Instead, a very simple method called procedural control is used.

procedural control

Before the invention of a more sophisticated system such as a secondary surveillance radar, pilots could simply turn over position reports to locate aircraft very simply. The report will contain information about the position, altitude and speed of the aircraft. Air traffic control will record this and can build a picture of the aircraft’s current location, as well as where it will be in the next minutes and hours.

When flying across the Atlantic, a similar system called procedural control is used.

The busiest part of the North Atlantic is divided into a series of highways known as railroad tracks; Each track has input and output points.

Before starting the crossing, the pilots let air traffic control know their required altitude and speed for the crossing and the time they will arrive at the entry point. Air traffic control collates this information from all flights it wants to pass through and assigns each aircraft an altitude and speed depending on when they arrive at their entry point. The pilot must then fly exactly according to the instructions of air traffic control.

Doing this resulted in each plane flying at least 1,000 feet away from the others. If there are multiple planes at the same altitude, they will fly at the same speed, making sure that one does not overtake the other. So once an aircraft leaves radar coverage, air traffic control knows it will remain safely separated until it is picked up by radar on the other side.


The procedure control system worked well, but it needed a large safety buffer built in because it couldn’t track the aircraft in real time. As a result, fewer aircraft can cross the Atlantic in a given time, which sometimes leads to delays.

A system that allows air traffic control to know the exact position of an aircraft, even when out of radar coverage, is needed. So, automatic dependent monitoring broadcast system was created.

ADS-B works like a secondary surveillance radar system but in reverse. Instead of a ground station interrogating the transponder, the transponder itself sends a signal that other ground stations or aircraft can receive.

The name sounds a bit complicated, but it describes exactly how the system works. ADS-B is automatic because it does not require other systems to interrogate; it automatically sends its own data. It depends because this information depends on data (such as aircraft position) provided by the aircraft system to send monitoring information to other stations. Finally, this data is broadcast and the sender does not know who will receive the signal.

The main benefit of ADS-B communications is that instead of requiring the reach of a ground-based radar station, the signal can be transmitted into space. Satellites then redirect it back to air traffic control, allowing air traffic control to see exactly where an aircraft is and what it’s doing in near real time. A great example of this is flight tracking programs like Flightradar24.


Sites like Flightradar24 use a variety of data sources to allow users to view an aircraft’s location almost anywhere in the world, plus data like its altitude, speed, and direction. This is because these sites can access the ADS-B receiver to get the correct data.

Most of this data comes from ground-based ADS-B receivers, but when aircraft are out of range — such as when flying over the Atlantic — they can also access data released by satellites. transmission. This means the information is so accurate that you can watch a plane fly past you on your phone at the same time it flies over your head.

Aircraft tracked by ground-based ADS-B receivers are shown in yellow, while aircraft tracked by satellites are shown in blue. FLIGHT RADAR24

bottom line

Modern technology on commercial aircraft is so good that air traffic control can track an aircraft’s position even while it’s flying over the ocean. ADS-B’s accuracy improvements have allowed air traffic control to reduce the minimum horizontal distance of aircraft over the Atlantic from 60 miles to 30 miles and increase the frequency of communications between the aircraft and the surface station. land. As a result, almost twice the number of transatlantic routes can occur at any given time without an extended period of silence, allowing multiple aircraft to perform optimally and economically. fuel safely.

While we may never find out the reason behind the disappearance of MH370, the tragedy has brought much-needed advances in tracking technology to ensure most aircraft can sustain connects to those on the ground, no matter where they’re flying.


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