Guide
Flight tracking basics
A live flight tracker shows aircraft positions that the aircraft broadcast themselves. Most planes send their position, altitude, speed and identity by radio about twice a second. Thousands of volunteer-run receivers on the ground pick up those signals and feed them to a network, which puts every aircraft on one map within a few seconds.
Where the positions come from
The main source is ADS-B (Automatic Dependent Surveillance–Broadcast). An aircraft with ADS-B Out works out its own position from GPS and broadcasts it, along with a unique 24-bit address, its callsign, barometric altitude, ground speed, track, vertical rate and squawk code. "Automatic" means no one has to ask; "dependent" means the position depends on the aircraft's own navigation system; "broadcast" means anyone with a receiver can listen.
Since 1 January 2020 the FAA has required ADS-B Out for most aircraft flying in the busiest US airspace, so nearly every airliner, business jet and a large share of light aircraft now broadcast. Aircraft that only carry an older Mode S or Mode C transponder can sometimes still be placed using multilateration (MLAT), which times the same signal at several receivers. Our guide to ADS-B vs MLAT covers the difference.
Who receives the signals
ADS-B signals travel by line of sight on 1090 MHz or 978 MHz. A small antenna and an inexpensive software-defined radio can hear aircraft 100 to 250 nautical miles away, depending on altitude and terrain. Hobbyists, airports, flight schools and enthusiasts run these receivers and share what they hear.
airplanes.live is a community network of these volunteer feeders. Its data is unfiltered: it shows what receivers actually hear, including many military and government aircraft and aircraft whose owners have asked the FAA to limit display of their data in FAA-sourced feeds. heywhatsflying.com reads a snapshot of the US portion of that feed and turns it into national statistics, lists and a map.
What a tracker can show you
- Identity: the 24-bit ICAO address (hex code), callsign, and usually the registration and aircraft type from a database.
- Position and motion: latitude, longitude, altitude, ground speed, track and vertical rate.
- Status: the squawk code, including emergency codes, and the emitter category (light, heavy, rotorcraft and so on).
To decode each field, read how to read flight data.
How "live" is live?
Aircraft broadcast position roughly twice per second. Receivers forward messages almost instantly, and the network aggregates them every second or so. heywhatsflying.com then refreshes its national snapshot about every 10 to 15 seconds and pauses when your browser tab is hidden. In practice, what you see is typically 5 to 30 seconds old. That is close to real time for curiosity, but it is not a substitute for air traffic control, and nobody should use it for navigation or safety decisions.
Why some aircraft are missing
- No receiver in range. Coverage is excellent over cities and busy corridors and weaker over oceans, deserts, mountains and remote parts of the West. Low-flying aircraft drop out first because terrain blocks line of sight.
- No ADS-B Out. Aircraft flying outside mandated airspace, such as some light aircraft and gliders, may carry only a basic transponder or none at all.
- Turned off for a reason. Some military, law enforcement and other sensitive government flights operate without ADS-B, as allowed by FAA rules. See why military aircraft show or don't.
- On the ground. Many aircraft switch off transponders while parked. Airborne counts exclude aircraft reporting "ground".
National view vs local view
heywhatsflying.com answers "what is flying right now, across the country?": the total airborne count, the highest and fastest aircraft, emergencies, military and government flights, helicopters and the most common aircraft types. If you want to know what is flying over your own house, our sister site heywhatsabove.com uses your location to show nearby aircraft and where to look in the sky.
Using the data responsibly
ADS-B broadcasts are public radio signals, and tracking them is legal in the US. Still, behind most aircraft are real people: patients on air ambulances, crews having a bad day, owners who value privacy. We show national aggregates and notable aircraft, avoid speculation about emergencies or military missions, and point you to the airplanes.live globe when you want to dig into an individual flight's track.
Next steps
- See the live national map.
- Look up a specific aircraft by hex code on the aircraft lookup page.
- Learn the vocabulary in the glossary.
Questions
How do flight trackers know where planes are?
Most aircraft broadcast their own GPS position, altitude, speed and identity using ADS-B. Volunteer-run ground receivers pick up the signals and share them with networks such as airplanes.live, which combine them into a live map.
How delayed is live flight tracking?
Aircraft broadcast about twice a second and networks aggregate within seconds. On heywhatsflying.com the national snapshot refreshes about every 10 to 15 seconds, so positions are usually 5 to 30 seconds old.