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When A Flight Vanishes From The Sky, Amateur Trackers Know It Instantly

Twice this year a Malaysia Airlines jet has disappeared. And each time, anyone with an Internet connection could discover, immediately, the plane’s last known location, other planes in the area, where they came from, what time they took off, and where they were going.

This rich repository of flight data, available free on websites such as Flightradar24, FlightAware and Plane Finder and related apps, comes courtesy of aviation enthusiasts around the world who set up equipment in their homes to scan the skies. Particularly valuable are plane geeks who live near airports, on remote oceanic islands or in Africa, and they can often get the equipment for free in return for sending in what they find.

The data from their scanners, supplemented with time-delayed information from the U.S. Federal Aviation Administration, adds up to a map of the world’s skies, with about 100,000 flights moving across them each day. The information has uses that go far beyond tracking air disasters. Taxi drivers can watch their passengers’ passage and time their pickups. Pilots can decide when to drive to the airport to meet their incoming planes. And sky watchers can satisfy their curiosity about the jets they see and hear flying thousands of feet above.

These lofty data sets arose from modest beginnings: Private pilots in the U.S. who wished their families could track their progress started FlightAware; Plane Finder stemmed from Ship Finder, started by big-boat watchers in southeast U.K. ports.

Two Swedes started Flightradar24 as “link bait” for their fare-comparison website, chief executive Fredrik Lindahl said in a Skype interview. “It quickly turned into something else.”

Mikael Robertsson and Olov Lindberg met when they were teenagers, at a demo party — a weekend retreat to create computer demo graphics and to socialize. Years later, Robertsson quit his job at a price-comparison website and got in touch with his old friend, Lindberg. “We met for a lunch, and just during this lunch, we found out that we are a team; we should start a company together,” Robertsson said via Skype.

Their main interest wasn’t tracking flights; it was helping people find cheaper ones, through a website they called Flygresor. They erected plane-location data receivers on their Stockholm homes to pick up transmissions from local planes, then put screenshots of the traffic they picked up online, hoping to attract clicks to their flight-comparison site.

Eventually, Flightradar24 became their main focus. They brought in Lindahl, Lindberg’s former classmate, to run the company two years ago.1

Data receivers work by picking up planes’ transmissions of their locations. (Flightradar24 sends out 50 free receivers each week, and I bought a cheaper version online for $40.) Older planes typically get their location information from ground radar. The next generation of aviation technology locates planes using satellites. Planes with that equipment have more accurate location information. The FAA has mandated that all electrical aircraft use the next-generation equipment — automatic dependent surveillance-broadcast, or ADS-B — by 2020, a process that so far has crawled.

The websites supplement the ADS-B data with transmissions from older, less precise technology, which their network of receivers also picks up. Since last year, Flightradar24 has used something called multilateration, which requires four or more receivers to pick up the difference in time of the arrival of signals from older, Mode-S technology.2

Also, the FAA releases data on planes over the U.S. and Canada, plus those originating from or going to those destinations, with a five-minute delay.3 Few equivalent aviation agencies in other countries release such data publicly, with or without delay, though anyone with the equipment and requisite ability to interpret its output can identify and locate planes in his or her area.

“In order to balance freedom rights with security, the FAA releases it, but releases it in a delayed manner,” said Ric Peri, vice president of government and industry affairs for the Aircraft Electronics Association. The group represents companies that sell flight-location equipment to airlines and aircraft manufacturers.

The companies that publish the data say its availability makes us safer. After all, if those who shot down Malaysia Airlines Flight 17 didn’t mean to shoot a passenger jet, the shooters might have avoided the mistake by using one of the sites, said Mark Duell, vice president of operations at Houston-based FlightAware, in a telephone interview.

And any terrorist who might intend to shoot down a passenger jet could see and hear it once it’s in range; these sites wouldn’t help much, Duell said. Anyone who wanted advance notice of a given plane’s location for nefarious reasons and could afford a surface-to-air missile could also easily afford his own flight-tracking equipment anyway, and so wouldn’t need these sites. They’d be using information anyone can get, because aviation authorities have decided the benefits of everyone knowing where planes are, to avoid accidents and increase transparency, outweigh the risks.

The data also makes it possible to answer such questions as how many flights passed through the Donetsk area4 of Ukraine in the week before Malaysia Airlines Flight 17 was shot down there. (Answer: 830, according to Flightradar24.)

“I have no concerns that the data is public, or could fall into ‘the wrong hands,’” Jason Rabinowitz, who feeds data to Flightradar24 and Plane Finder from his home in Nassau County, New York, said in an email interview. “After the crash of Malaysia 370 and 17, the entire world turned to Flightradar for answers, data that may not have been available anywhere else.”

Some planes don’t want to be located: military planes, say. The sites say they respect any block requests and obscure those planes’ information, though “the occasional one gets through,” Duell said. That happened to Flightradar24 in 2011, when Air Force One flew to Stockholm and was tracked online on the way. Oops. “Our intention was not to show Air Force One,” Lindahl said. “Due to technical problems, it did show up.”

The plane-location companies’ focus is on expanding their data sets by getting more receivers out into the world. The equipment is compact. The more expensive receiver Flightradar24 uses weighs half a pound and is about 3 feet long and 3 feet wide. The cheaper one is a USB stick and a tiny antenna.

I opted for the cheaper one. It arrived at my London apartment from Germany a week after I ordered it. It took about an hour to set up and get running. The process isn’t for the timid. I followed the instructions provided by FlightRadar24, which involved installing a few different files, including two different kinds of zipped files and a program just to unzip one; overriding the default Windows process for installing drivers; finding the precise latitude and longitude of my home; and positioning the antenna on my balcony, which upped the number of aircraft it found from zero to as many as nine. Even after following the instructions to the letter, I was stymied until reading deep into the help forum and then realizing I needed to restart one of the programs to save the settings.

The payoff was a bit anticlimactic. I was hoping for a map of planes in the London sky whose data I was receiving. Instead I saw a series of codes that meant nothing to me. But I was feeding my data into the greater collection, and obtaining free access to the premium version of the site.

A screen shot from FlightRadar24 Premium shows planes in the sky over London. The green line represents the plane whose path we followed.

A screenshot from Flightradar24 Premium shows planes in the sky over London. The green line represents the plane whose path I followed.

FlightRadar24 Premium

More experienced users track their own stats and hunger for confirmation that it is their antenna, and not some other user’s, that’s picking up the data used to locate a plane in the sky. I found some of these users in the forum thread where I was hunting for technical advice, until they were shut up by a post saying, “This thread is for issues with the feeder software. Not your disappointment at glory.”

Not everyone signs up for glory. Rabinowitz has been feeding data to Flightradar24 for two years. He lives two miles from John F. Kennedy Airport in Queens, New York, and when he joined, there was reliable coverage in New York City only from 10,000 feet and higher. The sites need receivers close to airports to get good coverage of planes at gates and runways.

“Setting up a local receiver simply meant better coverage in NYC,” Rabinowitz, a data research manager at the flight-finder site, wrote in an email. Rabinowitz now uses free flight-tracking hardware from Flightradar24 and Plane Finder. “Coverage for both services has gone from about 10,000-feet-and-above only to ground-level-and-up coverage at JFK and about 200 feet and up at the other airports” in the area, Newark Liberty and LaGuardia.

All the sites offer to send free equipment to people who fill a gap in their coverage. Earlier this year, Flightradar24 targeted Facebook ads at Bermuda residents and received a dozen applications within a week. Last month, it sent out 20 to 30 receivers to people in countries in the southeast of Africa, a continent that looks mostly devoid of air traffic on the sites’ maps, because the companies lack a rich network of African contributors. Flightradar24 has a network of about 4,500 receivers worldwide.

In the company’s early days, the equipment wasn’t as simple as it is today. Though Robertsson didn’t set out to start a flight-location company, he’d always loved planes and travel. He remembers fondly traveling to meet with partners around the world to help them get set up. He relished the journeys to remote locations, such as the Canary Islands — not, as he’d done before, to the tourist spots, but to someone’s home, to meet a local resident and work with him.

Robertsson sometimes scans world maps, looking for islands he doesn’t know. “It’s funny to find these small islands, find out if there is electricity, find out if someone is living there, if it is possible to go there,” Robertsson said. “My dream is to go to every small island in the world and install a receiver.”5

When he’s not studying maps or screening applications for new network partners, Robertsson sometimes still stares at his computer screen, watching his little animated planes inch through the monitor-sized sky. “I zoom in [on] some area around the world and watch what type of aircraft fly over that, where they are flying, which routes,” he said. “I think it’s fascinating when it’s live and it’s updating and something is happening. That makes it so fascinating.”


  1. They sold Flygresor in January, to the online travel agency European Travel Interactive. Now Lindberg runs Flygresor while Robertsson is chief product officer of Flightradar24.

  2. Plane Finder is introducing MLAT soon, Mark Daniels, director at Portsmouth, U.K.-based Pinkfroot, Plane Finder’s parent company, said in a telephone interview. Flight Aware hopes to in the next year, Mark Duell, vice president of operations at Houston-based FlightAware, said in a telephone interview.

  3. Flightradar24 has been incorporating this data into its maps since 2012.

  4. Within 86.4 miles

  5. Receivers need power and an Internet connection. “We already have receivers at remote locations that are visited only infrequently,” Flightradar24’s Lindahl said.

Carl Bialik was FiveThirtyEight’s lead writer for news.