I have to admit I've only flown in simulators but everyone of them implements the "CLR" button of the transponder in an A320 (maybe also others) the following way:

  • It removes the fourth digit only if present
  • Otherwise (meaning at most three digits defined) it clears the complete code

Why is it that way and why doesn't it either clear each digit individually, or all digits every time?

  • 1
    $\begingroup$ It might be good to know what kind of flight simulators you have experience with because not all are intended to emulate each function of the real aircraft. $\endgroup$ Jun 1, 2021 at 16:12
  • $\begingroup$ I've tested it myself on the FS Lab A320, but seen in on the Flightfactor and MS2020 A320s. $\endgroup$
    – xZise
    Jun 2, 2021 at 20:44
  • $\begingroup$ Well hopefully someone with A320 experience will chime in here, but I can tell you from experience that not everything in MS functions like it does in the real airplane. Consumer PC simulators have gotten pretty darn good, but they are after all really just games so I wouldn't put too much stock on them being accurate... $\endgroup$ Jun 2, 2021 at 21:08
  • 1
    $\begingroup$ Not a pilot, but it seems pushing CLR shortly clears the last digit entered, pushing 2s clears all digits. At least on a Gables ATC-TCAS panel. $\endgroup$
    – mins
    Jun 4, 2021 at 17:58
  • $\begingroup$ It may be linked to the fact that when you enter the last digit the previous code is removed, while if you enter only 3 digits or less, the previous code is still active. $\endgroup$
    – ocirocir
    Sep 13, 2021 at 9:02


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