An Inside Look at Flightradar24, the Team Watching Every Airplane in the Sky

STOCKHOLM, Sweden -- Keeping track of every airplane in the sky -- all 14,000 of them or so at any given moment -- is a heady task but one a team of travel enthusiasts in Stockholm, Sweden, are able to do with unparalleled detail due to a high-tech network of receivers positioned around the world.

Flightradar24, which had its first breakthrough in 2010 after an Icelandic ash cloud grounded thousands of flights, has since grown into the go-to source for everyone from aviation enthusiasts to media outlets and even governments looking for answers after an air traffic disaster.

"I would say that the credibility of our data has grown tremendously. Media turns to us immediately," Mikael Robertsson, one of the co-founders of Flightradar24 told ABC News recently during a visit to the company's Stockholm headquarters. Government agencies are also looking to Flightradar24 and its trove of data, Robertsson said, noting that a group of government officials recently visited the company's headquarters.

"They use our data and want to know how to access it quicker," he said.

How They Do It

What began as a secondary business to an airfare price comparison website has grown into a lucrative business for Flightradar24, which sells its app for $3.99 and also offers subscriptions geared toward businesses and consumers.

Fredrik Lindahl, CEO of Flightradar24, told ABC News the company has about 1.5 million users per day from around the world.

The competitive edge behind Flightradar24 is the company's network of 10,000 receivers scattered around the world. They're on top of office buildings, at airports or even on the roofs of homes owned by aviation enthusiasts. An antenna on the roof is wired to a receiver inside that collects the data.

"With 10,000 receivers, we cover more or less the land mass around the world. We have some gaps in China, Africa but pretty much all the land is covered," Robertsson said.

Every airplane is equipped with a transponder and sends out what's called an ADS-B signal. If an airplane is flying off the coast, it can make contact with a receiver 150 to 200 miles away, Robertsson said. The receivers upload data to Flightradar24's servers every five seconds.

"The transponder is transmitting data twice per second," Robertsson said. "So, during five seconds the receiver is picking up ten times from an aircraft but uploading only one package, so we are dropping a lot of data."

When Disaster Strikes

Robertsson and Lindahl said their busiest day ever was due to the Icelandic ash cloud, when people were apparently fascinated by the empty airspace and checking their website. But perhaps the most puzzling day was when Malaysia Airlines' Flight MH370 disappeared.

"The news came out just before midnight Swedish time," Robertsson said. "I remember I was just about to go to bed and I saw on some media there was an aircraft missing so I started to check our data and I could see that we had this aircraft in coverage as it left the Malaysian coast. I think about 20 minutes later it just disappeared and then media started to report this aircraft has crashed in China, Vietnam, some reported it landed. So much different information was coming out and it was just a big mess."

Robertsson pulled the last data point Flightradar24 had for MH370, which was just off the Malaysian coast, and said he tweeted about it and posted on Facebook, hoping to help bring some clarity to what had turned into an echo chamber of misinformation.

For about 12 hours, there were numerous incorrect reports "about crashing and fires and landing," he said. "And then media started to go back and check, 'What do we really know?' I think that is the first time maybe that media trusted the data we had and started to report the last position was outside the Malaysian coast. It took between 12 and 24 hours, I think, before the reporting was more correct."

Four months later, after MH17 was shot down and crashed in Ukraine, it took just five minutes before Flightradar24's servers crashed.

After the first Malaysia Airlines incident, Robertsson said Flightradar24 began recording all of the data from a receiver so they could easily retrieve it in the event of a disaster.

"Everything is saved in the box, so if something happens we can go back and download the data," he said. "A receiver can only have five to ten hours of data before it is running out of memory so it's overwriting and we have to act quite fast when something happens to go back and get the data."

Immediately after the March 24, 2015, crash of Germanwings Flight 9525 in the French Alps, the Flightradar24 team downloaded the data from their receivers and saw a clear picture of what appeared to be a controlled descent, signalling the crash was intentional.

"We didn't go public with until the authorities said he [the co-pilot] basically committed suicide, but we could see," Lindahl said. "We figured it wasn't our place to do that before the authorities but after that we shared the data [with authorities]."

Watching It Live

The unanswered questions of a tragedy are part of what brings people to Flightradar24, but Robertsson and Lindahl said they have also noticed a spike in curiosity when people want to follow an aviation event as it unfolds.

Visitors watched as an American pilot and his wife, who were unresponsive, flew past their destination in Naples, Florida, and continued flying to the Caribbean before the plane crashed off the coast of Jamaica, killing the couple.

Traffic spiked another time when a cargo aircraft needed to return to the airport in Amsterdam but first needed to shed some weight by dumping fuel.

"They were circling outside the coast of Holland for one or two hours and someone in Dutch media picked up this aircraft is holding outside the coast and they put it on the first page and other media in Holland picked this up and it was everywhere in Dutch media that this aircraft is holding," Robertsson said. "This is something that happens more or less every hour anywhere so it isn't big news but it was more or less the first time Dutch media picked this up and they made it so big so we had 50, 60, 70 thousand people from Holland on the site watching this aircraft go around and around in circles."

Covering the Oceans

While their network is expansive, Robertsson and Lindahl said they're looking to make their coverage truly global, which means tackling a difficult problem: how to cover the oceans.

The company's 10,000 receivers are dispersed around the world and cover ranges of up to 150 to 200 miles, but this leaves coverage gaps for the thousands of flights that cross oceans every day. Among the options the company is considering, according to Robertsson, are satellites or ships equipped with receivers.

Balloons have also caught the attention of the Flightradar24 team. Google has experimented with launching internet-beaming balloons into the stratosphere, something Robertsson said could be a solution for achieving global coverage for Flightradar24.

"Google, for example, is sending up balloons that can stay up for 100 days, so we are not talking balloons that stay up a couple hours but maybe we can send up balloons that could stay up for weeks or months," he said.