Wow, Friendly Pelican... Like you're saying. There is NO WAY to catch that error at, before or past transition level. Garbage in is garbage out... If you're new to the bus it is worth noting that the FMG(E)C has a model of the standard atmosphere incorporated into it. Hence the 36090' for the tropopause on the init page. That's also why ISA deviation is only showing when the Captain's altimeter is set to STD (A320, A330, A340). When descending the level at which the STD box starts blinking is dependant on the QNH input on the PERF page.