Now, I understand that there is not an exhaustive list, but how do I know then?
There is caselaw decided by the ECJ, and we can also rely on the practice of the local courts. We just want to give you some example:
We have a long list for that, let us give you some example:
Contact us! It is possible that although extraordinary circumstances indeed happened, but that was not the direct cause of the flight delay, or the airline could have reasonably expected to avoid that. These cases are sometimes difficult, and needs individual assessment.
Well, let say that you travel from London to Budapest. There was indeed an accident two days ago, (two planes collided, fortunately no one was harmed), but there was a slight disruption in the operation of the airport, and therefore some planes were delayed, but it is hard to believe that this can reasonably affect any flight two days later.
Even if the claim for extraordinary circumstances is justified, you have the right for meal and accommodation, and if you (reasonably) spent more than the value of the voucher that the airline provided you, it must be reimbursed.