Jetsbest - My typo.
Further, I was of the understanding that AFTER a CRITICAL SYSTEM failure.
The maximum diversion distance or EDTO limit takes into account other system failures. So that in the event of the sH#t really hitting the fan the aircraft was within a reasonable range of an airport to land at.
The certification of maximum diversion distance limitations takes into account additional system features or failures such as:
Cargo Fire Suppression
Cargo Fire Hold (lining) containment
Propulsion on the remaining engine
Equipment Cooling
Ice protection Failures (should you be down single engine / depressurised picking up ice)
So its not only the initial critical system failure, but the what if's if something else fails later.
MC