Thanks to all those that replied. I always learn something new.
I think this thread makes evident that while we may think that decision rules for ETOPS/"land at the nearest suitable airport" are clear, they are far from it. What is "suitable" can be open to debate based on runways, weather, fuel, MLW and distance to the next-best "suitable" airport. This seems so complicated that it is unlikely that a comprehensive a priori decision tree can be established. In the end, the decision must rely on the circumstances of the particular incident, and the decisionmaking prowess of the flight crew and dispatchers. That's why you guys should get paid as much (or more
) than you do.
Note: I only referred to ETOPS/two-holer decisionmaking because at least it does start from some baseline rule of general applicability (land at the nearest suitable airport). As we all know from BA B747 ex-LAX, permitted decisionmaking for 3's and 4's is even more untethered from predefined rules.