Right...don't transponders just have basically an off/standby/on switch, and then the buttons or dials for the code, and then the "ident" button that causes your information to flash or light up for the controller, so he can confirm it?
I can see somebody like me screwing up and accidentally putting 7500 in a transponder (momentarily), and I've heard stories about that happening before. But somebody flying an A330 or A340 across the Atlantic with 271 people onboard? Both members of the crew are NOT going to be newbies. That's a huge screwup, if that's what it is.
}:-)4
The system isn't perfect. A few years ago I was at cruise in a C150 below San Jose. ATC suddenly thought I had a 7700 code. My code wasn't even close. It was some kind of glitch on their end. I think the codes are assigned such that they aren't close to the special codes so that when you change codes you shouldn't hit them, at least if you careful.
That's how they worked when I was flying. Also I'm pretty sure that ATC doesn't assign codes like 7502 to anyone, so the chance of putting up one of the reserved codes, even for a couple of seconds, when switching to a newly assigned code is small. Normally these codes are not changed during a flight either, so there would be no reason for a plane to begin displaying 7500 instead of its assigned code.
ML/NJ