Why flight trackers lose planes over the ocean

You are following a flight across the Atlantic and halfway over, it stops moving, or vanishes. Nothing has happened to it. It has flown out of earshot of the receivers that feed the map.

Trackers hear aircraft, they do not watch them

Public flight trackers mostly do not use radar. They use ADS-B: a message every aircraft with the equipment broadcasts about once a second, with its position, height, speed and identity. Thousands of receivers on the ground, many of them run by volunteers at home, pick these messages up and send them to the tracker, which puts them on a map.

A receiver can only hear an aircraft it has a line of sight to. Flightradar24 says a typical receiver covers 200 to 250 km, and up to about 400 km when it is well placed; FlightAware gives about 480 km at most, for an aircraft at cruise height. Beyond that, the curve of the Earth gets in the way.

Where the gaps are

• Oceans. Out of sight of the coast and of islands, there are no receivers on the ground at all. Before satellites, controllers over the North Atlantic had a position for each aircraft only every 10 to 14 minutes, according to NAV CANADA.
• Deserts, polar regions and remote land. Few people live there, so few receivers are set up.
• Mountains. Ridges block the signal, especially for aircraft lower down.
• Low level. An aircraft on the runway or a few hundred feet up is heard only by receivers nearby. At a small airport with no receiver close by, a track may start in the air and end before it lands.
• Interference. Jamming of satellite navigation can corrupt the position an aircraft broadcasts, which is why tracks sometimes jump or vanish over certain regions.

The FAA gives an example from before ADS-B: over the Gulf of Mexico there was no surveillance at low altitude, or beyond 200 NM from the coast.

Satellites fill the gaps

Since 2019, receivers carried on Iridium's satellites have picked up the same ADS-B messages anywhere on Earth. The constellation, 66 satellites in low orbit, was complete in January 2019, and NATS and NAV CANADA were the first to use the data, over the North Atlantic, from 27 March 2019. NAV CANADA reported that it let controllers space aircraft much closer, cutting the gap between aircraft one behind the other from about 40 NM to 14 to 17 NM. Aireon, the company behind it, says more than half of the world's airspace was using its data by 2023.

Public trackers have started to use it too, with limits. Flightradar24 added satellite data from Aireon in February 2026; outside the reach of its receivers on the ground, positions from it appear every 15 minutes, with the aircraft's icon in blue. FlightAware sells it in its commercial products.

How airlines and controllers keep track

Over the ocean, aircraft also report their position by datalink, through ADS-C, a contract with the control centre to send reports at set intervals, on demand, or when something happens. Since November 2018, ICAO has asked airlines to track their aircraft at least every 15 minutes, and its rules now require it for the largest aircraft over oceanic areas where controllers get reports less often. The requirement came after Air France 447 in 2009 and Malaysia Airlines MH370 in 2014.

None of this reaches public trackers by default. So a flight that is plainly visible to its airline and its controllers can still show a gap on your screen.

Estimated positions

When an aircraft flies out of range, some trackers keep moving its icon along its expected route. Flightradar24 draws these estimated positions with a dotted trail, and has said it estimates for up to a few hours on flights with a known route. An estimate is useful for an arrival time and misleading for anything else: the aircraft may have turned, climbed or held while the icon carried on.

How FlyScout handles gaps

FlyScout never fills a gap with a position the aircraft did not send. On its map, an aircraft still flying stays where it was last heard until the next real position arrives. A gap in the record stays a gap; the only exception is where an aircraft turned while out of range, and its own reports of its course before and after the gap say how it turned, in which case the map draws that turn rather than a sharp corner.

Gaps also matter for finding unusual flights. A hold or a go-around flown where no receiver can hear it cannot be found, and a track with long gaps cannot be measured well. That is why FlyScout measures each event on the aircraft's whole recorded track rather than a few snapshots, and says when a path's positions were calculated by the receiver network rather than broadcast: see MLAT explained.