14 hours after EgyptAir Flight 804 disappeared from radar while en route from Paris to Cairo, Egyptian, Greek, and American aircraft and ships are gathering around the Greek island of Karpathos in the southern Aegean Sea. Wreckage has shown up near there, and they’re searching for survivors, of course—66 people were on board the Airbus A320. But they’re also beginning the massive and complex operation that starts any time a jetliner crashes or disappears. It’s search-and-rescue, but also an attempt to figure out what actually happened. (A few hours later, an EgyptAir official said that wreckage was unrelated to the missing jet.1)

Around 3 am local time, just after reaching Egyptian airspace and about 30 miles from the coast, flight 804 made a hard left turn, then a full circle to the right, Greek defense minister Panos Kammenos said in a press conference. It dropped from its 37,000-foot cruising altitude to 15,000 feet, then to 9,000 feet, and disappeared from radar a few minutes later. French President François Hollande told reporters “this plane crashed at sea and has been lost.”

So what comes next? An early priority is to find the most helpful tools in any investigation: the cockpit voice recorder and flight data recorder, the so-called black boxes. Built to survive just about anything, they’re actually bright orange and carry locator beacons that signal when they hit water. The recorders will send out pings for several weeks, and work just fine even under 14,000 of ocean.

The recorders are valuable to investigators because they contain two hours of audio recording from the cockpit and dozens of datapoints from the entire flight, including altitude, airspeed, and heading, along with the positions of individual controls and flaps at any given moment.

Meanwhile, the investigation team will start pulling together other relevant information, including flight crew and aircraft histories, weather data, radio communications and radar tracks, and witness testimonies, if any exist.

Search parties will gather and carefully log every piece of debris they find. That’s not as tricky as it sounds. “Every manufacturer puts a data tag, or data plate, on every part that goes on an airplane,” with the exception of things like screws, former NTSB investigator Greg Feith told WIRED last year. Basically everything should have a serial number, bar code, or part number.

Those pieces, along with any human remains, might show signs of burning, other damage, or chemical traces indicating an explosion. Investigators will geotag all that, according to information from France’s Bureau d’Enquêtes et d’Analyses, so they can “analyze the circumstances of the accident and build the most precise scenario.”

None of this happens fast. Aircraft accident investigations commonly take two years to complete, despite the kind of speculation that has already started moving through the media. They’re painstaking because the amount of evidence is massive. But it’s the only way to determine what went wrong, how it went wrong, and why—and to keep it from happening again.

1Story updated at 17:20 EST to include update from authorities that the wreckage found near Karpathos is not related to EgyptAir 804.


Here’s How Experts Will Investigate EgyptAir 804’s Crash