Guides
Flight-tracking guides
Plain-English guides to what you see on a live flight tracker: where the data comes from, what each number means, and why some aircraft show up while others don’t.
How many planes are in the sky right now?
How many aircraft are flying over the US right now, live, plus FAA daily figures and how the count rises and falls by hour, weekday and season.
Airlines and operators: who is flying
Who is in US skies: major airlines, regionals, cargo, fractional jets, GA and military, and a table of common callsign prefixes with their operators.
Flight tracking basics
How live flight trackers know where planes are: ADS-B broadcasts, volunteer receivers, community feeds, delays and coverage gaps, explained simply.
ADS-B vs MLAT: two ways to find an aircraft
ADS-B aircraft report their own GPS position; MLAT calculates position from signal timing at 4+ receivers. How each works, accuracy, and the US mandate.
Why military aircraft show up on trackers, or don't
Why tankers and transports often appear on flight trackers while fighters usually do not: ADS-B rules, operational security, MLAT and military hex codes.
How to read flight data
What hex, callsign, registration, type, altitude, ground speed, track, vertical rate, squawk, category and "seen" mean on a live flight tracker.
Altitude and flight levels: who flies how high
How high planes fly in the US: the 18,000 ft transition altitude, flight levels, typical cruising altitudes by aircraft type, and our altitude bands.
ADS-B emitter categories explained
ADS-B emitter categories tell trackers what is transmitting: light, heavy, rotorcraft, glider, balloon, drone or ground vehicle. Full A0 to C7 list.
Helicopters, balloons and other oddities
What makes a flight "interesting right now": rare types, helicopters, balloons, gliders, blimps and survey orbits, and how to spot them on a live map.
Callsigns, registrations and hex codes
How flight numbers, callsigns, ICAO and IATA airline codes, N-numbers and 24-bit hex addresses relate, plus privacy programs like LADD and PIA.
Squawk codes explained
Every transponder code with a fixed meaning, from 7700 to 1200.
Glossary
Definitions of 49 flight-tracking terms.
FAQ
Quick answers to the most common questions.