As part of its air transportation modernization effort known as NextGen, the Federal Aviation Administration (FAA) requires all private and commercial aircraft to continuously broadcast digital
information about the aircraft's identity, position, speed and other details using a system known as Automatic Dependent Surveilance–Broadcast, or ADS-B. Some, but not
all, military aircraft also transmit ADS-B data.
Anyone with an inexpensive radio receiver and the appropriate software can intercept these transmissions and thus gain live information about aircraft within line of sight of the receiver. Feeder networks of these receivers, usually operated by volunteers,
power flight-tracking websites such as ADS-B Exchange,
Flightradar24 and FlightAware.
This website makes use of ADS-B tracking data from a single receiver located about 2.5 miles south of the Madison airport. The receiver is also a feeder into the ADS-B Exchange flight-tracking
network, and the computer code used here for mapping aircraft information has been adapted from code developed for feeders on that network.
There are some limitations to the ADS-B information presented here:
Military fighter jets—including the Madison-based 115th Fighter Wing—typically do not transmit ADS-B data, and are thus invisible to the live mapping system here. (However they can later be identified based on their unique noise profiles across the network and validated in most cases with fighter-jet TIS-B tracks on ADS-B Exchange.)
Trees, buildings and other obstacles can block the signals, which can make aircraft appear to freeze or even disappear from the live map.
The receiver used here tunes the main ADS-B frequency used by all commercial aircraft and most private aircraft, but some general-aviation aircraft use a different ADS-B frequency and will thus not be visible on the map.
To show aircraft icons that correspond to the type of aircraft, the mapping code relies on crowd-sourced database lookups that may be incorrect or that may not exist for some individual aircraft. Occasionally the icon for an aircraft may start
out as one type, then change to another after it has been successfully retreived from a database. The aircraft details can be shown in the expandable sidebar of the live map and can be used to identify the manufacturer, model, and even ownership of a given aircraft.
