Transponder: Difference between revisions

Transponders are radio beacons which make aircraft more identifiable on ATC displays and systems. Modern transponders support transmitting additional data such as an identification ('squawk') code and aircraft altitude. See more at [http://en.wikipedia.org/wiki/Transponder_(aviation)]

See [http://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes] for official description. Civilian Mode-S and Mode-C both transmit pressure altitude (at 10-foot and 100-foot precision, respectively). To do this the transponder needs an altitude source. In real-life this can be a separate box called an encoder, or may be derived for FMC / ADIRU sources. It's important to note this altitude is referenced to standard pressure (29.92 inHg / 1012Hpa), and not corrected for actual barometric pressure in the local environment.