[BrianG]

That's called crowbar protection. As long as the BEC output voltage was lower than the zener voltage, things would run fine. If the BEC goes bad and the output voltage goes higher, the zener would basically short out the BEC causing it to either shutdown from overcurrent, burn up, or the zener would blow. Since the CCBEC can output over 7A continuously, you'd need one heck of a zener. Otherwise, as soon as it blew the voltage would go back up to whatever it is outputting. Not really an elegant solution IMO, but certainly simple enough.