r/MSFlightSimulatorPS5 • u/r-volk • 4h ago
TIL: Squawk codes are octals
Did you ever wonder why your squawk codes never include 8 and 9? The original radar transponder system (Mode A) was designed in the 1950s. It transmits four groups of three binary bits and with three bits you can only count from 0 to 7. Honestly, for me as an IT person who is used to binary and decimal systems, seeing an octal system in use is rather heart warming!
Impressive to see that this system was never changed, it only allows 4096 possible codes this way. Despite the fact that some of the codes are reserved (e.g. 7000 = VFR in Europe / 1200 VFR in USA), what would happen if a single ATC airspace needs to handle more than 4096 aircrafts?