How long does it take to change your code? I would think that, immediately you have been instructed to change code (I.e. ATC is EXPECTING a change) going STBY for, say 15 seconds while you dial up the new code and return to AUTO or ALT, is an expectation. What am I missing here?
Accidents happen when multiple factors combine. Lets say that there is 1:1000000 chance of engine failure during those 15 seconds. You get multiple warnings, you forget to turn on transponder, you start to descent, nobody know where you are, TA/RA is not working in other aircraft and just happens A380 flying 1000 ft below you. 500 lives lost just for turning transponder to STBY.