Aviation guides
The explanations behind the data on this site: how tracking works, what the codes mean, and how to read a fare or a delay.
Fifth-freedom flights, explained
A fifth-freedom flight is a leg an airline flies between two countries that are not its own, selling tickets on that leg alone. They exist because of how international traffic rights work, and they are a reliable place to find unusually good premium fares.
Read the guide →Squawk 7700, 7600 and 7500: what emergency squawk codes mean
A squawk is the four-digit transponder code an aircraft broadcasts so radar can identify it. Three codes are reserved worldwide for trouble: 7700 for a general emergency, 7600 for lost radio contact, and 7500 for unlawful interference.
Read the guide →How to track a flight: flight numbers, callsigns and tail numbers
A flight can be identified three ways: by the flight number on your ticket, by the callsign the crew uses with air traffic control, and by the registration painted on the aircraft. Trackers mostly speak callsign and registration, which is why DL123 shows up as DAL123.
Read the guide →What counts as an on-time flight? The 15-minute rule, explained
By the standard definition a flight is on time if it arrives at the gate within 15 minutes of its scheduled arrival. The rule shapes airline rankings, schedule padding and the delay figures you see on flight pages.
Read the guide →How ADS-B flight tracking works (and why some planes don't show)
ADS-B is the system by which an aircraft broadcasts its own GPS position, altitude, speed and identity about twice a second. Anyone with a cheap receiver can pick it up, and networks of volunteers pool those receptions into the live maps you see on flight trackers.
Read the guide →E175, E75L and E75S: what the Embraer E175 codes mean
The Embraer E175 has two ICAO type codes. E75S is the original short-wing aircraft built from 2005; E75L is the long-wing version delivered since 2013, with a wider span and new wingtips that burn about 6% less fuel. Inside they are the same aircraft, and airlines list both as an E175.
Read the guide →ICAO aircraft type codes, explained
What A20N, B38M, E75L and AT76 mean, how to read a type designator, the IATA equivalents, and a lookup list of hundreds of codes.
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