Why do planes vanish?

An airliner is followed by several systems at once. Secondary surveillance radar interrogates the transponder, which replies with identity and altitude; ADS-B broadcasts GPS position every second; ACARS sends short data messages over VHF or satellite; and the crew talk to controllers by radio. When all of these stop at once, the aircraft has, from the ground's point of view, vanished. Primary radar, which detects the reflection of the aircraft's skin without any cooperation, still works, but its range is limited by the horizon and by the size of the target: roughly 250 nautical miles (460 km) for the best civil installations, far less in practice. Beyond that, oceans and polar regions are outside radar cover altogether, and a flight relying on position reports by HF radio or satellite is only known to be where it last said it was.

Sudden loss of contact is rare and almost always has an ordinary cause: a transponder failure, a controller handover gap, an electrical problem, or in the worst case an accident whose location is known within minutes from the last data. Two cases account for most of the public sense that planes disappear. Air France 447 vanished over the South Atlantic on 1 June 2009 after its pitot tubes iced up and the crew lost control; ACARS messages showed the sequence but the wreckage was only found in April 2011 at a depth of about 3,900 m. Malaysia Airlines MH370, a Boeing 777 with 239 people on board, disappeared on 8 March 2014 after its transponder stopped some forty minutes into the flight. Malaysian military primary radar tracked it turning back across the peninsula, and hourly satellite handshakes with an Inmarsat ground station placed it in the southern Indian Ocean. Only a few pieces of debris have been found; the seabed search was suspended in 2017, resumed by a private company in 2018 and again in 2025, without result (data as of September 2026).

ICAO's Global Aeronautical Distress and Safety System followed. Since November 2018 airlines must know the position of every aircraft on oceanic routes at least every fifteen minutes, in practice through ACARS or satellite ADS-B. Aircraft built from 2025 onward must carry autonomous distress tracking that transmits position every minute when the flight is in trouble, using a source that cannot be switched off from the cockpit. Flight recorders on new aircraft now hold twenty-five hours of cockpit audio, and underwater locator beacons broadcast for ninety days instead of thirty. Space-based ADS-B, carried on the Iridium NEXT constellation since 2019, has closed most of the surveillance gap over oceans. An aircraft can still be lost, but the area to search has shrunk from hundreds of thousands of square kilometres to a few.