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　　A little-known "niche civil aviation good thing" became popular overnight.

　　Its real-time flight tracking function attracted 300,000 people last night, which directly caused the traffic to explode on this little broken website, and it collapsed for a while.

　　If you went to bed earlier, now you can take another look at the interface of this website called Flightradar24.

　　Just like that, the map will show all kinds of planes flying in the sky. Select the one you want to inquire (the small red plane in the picture), you can get detailed flight information, and see its real-time flight track on the map (purple line in the picture).

　　Is it quite convenient? With this artifact, female friends no longer have to worry about me being late for pick-up.

　　Closer to home, here are some knowledge points: How can Flightradar24 track the route so accurately, even Airbus, Boeing and other companies are using it?

　　Let's study it together.

　　Track flights with open source data

　　To put it simply, Flightradar24 mainly uses open source data to achieve flight tracking.

　　According to the official website, Fligtradar24 combines a variety of data sources, including ADS-B, MLAT, radar data, as well as airline and airport schedules and flight status information.

　　ADS-B

　　ADS-B stands for Automatic Dependent Surveillance Broadcast. This is the main technology used by Flightradar24 to receive flight information.

　　Basically, the technology works like this:

1. The aircraft determines its position through the satellite navigation system

2. The aircraft regularly broadcasts the position information through the ADS-B transponder installed on the aircraft

3. The relevant signal is received by the ADS-B ground receiver of Flightradar24

4. These data are synchronously updated to Flightradar24's website and app

　　In fact, not only is it useful for air traffic control on the ground and tracking sites such as Flightradar24, ADS-B also provides convenience for the pilots on board.

　　The ADS-B data includes the aircraft's altitude, heading, speed, and additional information such as conflict warning information and route inflection point information .

　　And compared with the radar surveillance system, ADS-B data update speed is fast, data accuracy is high, the transmission information is rich, and the installation and use costs are also much lower.

　　Therefore, on an aircraft equipped with an ADS-B receiving device, the pilot can also obtain traffic information and conduct autonomous avoidance to avoid collision.

　　Currently, most aircraft in the world are required to be equipped with ADS-B equipment.

　　Fligtradar24 has the world's largest ADS-B network with more than 30,000 ground receivers.

　　MLAT

　　But not all aircraft are equipped with ADS-B devices, and MLAT can be used to track them if they are not carried.

　　The full name of MLAT is Multilateration, which mainly uses the wireless positioning technology of Time Difference of Arrival (TDOA) to calculate the position of the aircraft without ADS-B equipment.

　　In simple terms, MLAT utilizes signals sent by older transponders on planes. By measuring the time it takes to receive a signal with multiple receivers, the aircraft's position can be calculated.

　　This method requires four or more receiving devices.

　　In addition to the two data mentioned above, Flightradar24's data sources also include satellite data, North American radar data, and North American real-time data from the Open Glider Network (OGN).

　　By the way, Flightradar24 has a lot of fun little features.

　　You can see the 3D effect of the plane soaring in the air.

　　ps. Some advanced features require payment.

　　From hobby project to the most popular flight tracking app

　　Now, Flightradar24 is one of the most popular travel apps in both the Apple App Store and Google Play, with over 40 million cumulative downloads.

　　However, Flightradar24 started out as a side project.

　　Mikael Robertsson and Olov Lindberg from Sweden noticed the ADS-B aircraft signal communication method out of interest.

　　So they bought a few small signal receivers and put them on the roof to track planes flying over Stockholm.

　　In 2006, they created a website to compare flight prices and added flight tracking to the site.

　　Soon, the model attracted a lot of aviation enthusiasts, and some people expressed their willingness to install receivers on their roofs to collect data for the website.

　　As a result, the tracking range of Flightradar24 has been further expanded.

　　By 2009, they officially opened the network to the outside world, allowing anyone with an ADS-B receiving device to upload data to them.

　　In addition, there are fans who helped them write a software that can obtain various information from the ADS-B signal.

　　It can be seen that the flight's origin, destination, callsign, location, altitude, airspeed and heading will be displayed on the Flightradar24 official website, and even data such as the aircraft's pilot instrument settings and remaining fuel can be provided.

　　Providing such timely and comprehensive information, Flightradar24 has also attracted many professional aviation personnel, such as air controllers to check the real-time situation of each aircraft.

　　Flightradar24 can also be seen in many major news events.

　　In 2010, a volcanic eruption in Iceland caused widespread flight cancellations in Europe, and many media were using Flightradar24 to track flight information.

　　In 2014, the Malaysia Airlines MH17 crash occurred, and Flightradar24 also provided a lot of information on the flight movements of the day.

　　The occurrence of these two events has brought huge traffic to Flightradar24.

　　According to founder Robert Song, the 2010 Icelandic volcanic eruption affected flight events, and the number of visitors to Flightradar24 exceeded 4 million.

　　In 2014, there were frequent air crashes, and the number of visits to the website increased by about 50 times that year.

　　It was also around this time period that Flightradar24 gradually transformed into commercialization, developed its own APP, and slowly expanded the scope of signal receivers from Europe to the world.

　　In addition, the US Federal Aviation Administration (FAA) has already required all aircraft, including private helicopters, to be equipped with ADS-B transmitters by 2020.

　　Now, Flightradar24 has grown into one of the most popular flight tracking applications in the world.

　　According to the official website, Flightradar24 tracks more than 180,000 flights every day, with more than 2 million daily active users.

　　One More Thing

　　It is worth mentioning that due to the wide range of aircraft using the ADS-B system, Flightradar24 filters some data to protect privacy.

　　However, there have also been accidents. For example, in 2014, the flight route and location information of the special plane taken by the Japanese Prime Minister and other senior leaders could be directly viewed on Flightradar24.

　　And there are many websites with similar functions like Flightradar24, such as ADS-B Exchange, FlightAware, OpenSky Network, Radarbox24, PlaneFinder and so on.

　　Among them, ADS-B Exchange is one of the more wild ones. It allows users to check the flight information of celebrities, politicians' private jets, and even military aircraft information.

　　As these sites grew, so did a lot of news about private voyages.

　　For example, it was found that this year Taylor Swift topped the list of celebrities for carbon emissions from flying in a private jet.

　　There are even 19-year-old high school students who have opened more than 30 robot accounts to disclose private jet flight information. Celebrities involved include Musk, supermodel Kari Jenner and more.

　　Earlier, an enthusiast said in an interview that the experience of tracking flight movements gave him a feeling of "bird watching".