4 ms·

Fun fact about octal: every commercial and most non-commercial aircraft have a transponder to identify with Air Traffic Control. The squawk code is in octal. h

• rplst8 10y ago
  A lot of the data buses on aircraft also use octal to identify the data words.
• privong 10y ago
  And the squawk codes are broadcast as part of the ADS-B system[0]. These packets can be received with the inexpensive USB software-defined radios (e.g., [1]). [0] https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_%E2%80%93_broadcast https://en.wikipedia.org/wiki/Automatic_dependent_surveillan... [1] http://www.rtl-sdr.com/adsb-aircraft-radar-with-rtl-sdr/ http://www.rtl-sdr.com/adsb-aircraft-radar-with-rtl-sdr/
• dingaling 10y ago
  And the civilian SSR system was built on the released frequencies and protocols of Mode 3 of the military Mark X IFF system, which was adopted by civilian agencies in the mid-1950s after a particularly nasty airborne collision. Sixty years later and we're still bounded by legacy. As a result of shortage the general-use squawk codes are namespaced into each national ATC region, so aircraft have to constantly change squawks even in supposedly contiguous regions such as Eurocontrol. Squawk 4463 means a different thing in UK airspace than in French. Ironically, military aircraft still support Mode 3 in order to integrate with civilian ATC, who call it Mode-A, but all their special don't-shoot-me-I'm-friendly stuff is handled by more modern encrypted protocols.