Most airplanes and other aircraft are equipped with — a device that transmits aircraft position and other flight information to an air traffic control centre. These same signals can be received by inexpensive receivers based on a technology called ADS-B. This is exactly what flight-tracking websites do, providing users with real-time snapshots of everything in the sky.
When a US Air Force plane carrying Speaker of the House Nancy Pelosi landed in early August, Taiwan, more than 700,000 people around the world witnessed this event using the Flightradar24 flight tracking service.
The aircraft, a military version of a Boeing 737 called a C-40, took off from Kuala Lumpur in Malaysia before heading to Taiwan on a rather bizarre detour to avoid clashes with the Chinese military. This increased the flight time by several hours. It was not immediately clear to observers what the final destination would be, sparking controversy on the Internet, until finally the plane turned north towards the island. As a result, it was Flightradar24's most tracked flight ever, with 2.92 million people following at least part of the seven-hour journey.
Flightradar, part of a group of popular flight tracking services along with FlightAware and Plane Finder, was founded in Sweden in 2006. Moreover, the goal was to attract additional traffic to the airfare comparison service.
It first gained worldwide recognition in 2010, when the eruption of the Icelandic volcano Eyjafjallajökull canceled thousands of flights and attracted four million visitors.
There were other significant events followed by users all over the world through Flightradar24.
In April 2020, almost 200,000 users watched the Boeing 777 draw the crescent and star — symbols of the Turkish national flag in the sky over Ankara — during the celebration of the 100th anniversary of Turkish sovereignty.
Prior to this, in September 2017, thousands watched Delta's plucky Boeing 737 fly straight into Hurricane Irma, land in Puerto Rico, and take off for New York 40 minutes later, flying neatly between the hurricane's branches.
However, even in the absence of major events, the number of people tracking flights is constantly growing. Many use the site to track down a loved one, their own flight, or find an incoming plane to fly later in the day.
Among interested observers — those who rent equipment and they want to monitor it in the sky. Finally, it is the airlines themselves, airports, aircraft manufacturers, who use large amounts of data to obtain information about the industry.
To collect data, Flightradar built its own network of ADS-B receivers, which, according to them, is the largest in world and has about 34,000 units, covering even such remote areas as Antarctica.
About a quarter of the receivers are owned by Flightradar24, but most of them are built by enthusiasts who provide data on a voluntary basis. Since it is relatively easy to assemble the apparatus — all components cost around $100, many of which have come into the system since Flightradar24 began opening up its network to the general public in 2009.
Receiver density affects the clarity of flight tracking around the world, but over oceans objectively there are holes. In this case, the islands and satellite equipment ADS-B are used to the maximum.
Having such a granular and localized amount of data can be useful for getting an early picture of emergencies and accidents: All incoming information is stored on servers, and if necessary, you can go back to a specific date and extract the original data. This is usually done if an accident has occurred or if there is an official request from an air navigation service provider or an accident investigation department.
Sometimes data can reveal the cause of an accident before an official investigation does. In the case of Germanwings Flight 9525, which was deliberately driven uphill by the co-pilot on March 24, 2015, the data paint a very clear picture: one of the parameters included in the most complete data package, — this is the altitude given by the pilots to the autopilot. Well, this altitude value has been set to zero.
Aircraft owners and operators can choose not to display their data publicly, most commonly for military, government or private aircraft — only about three percent.