Originally Posted by
Often1
ATC seems to be the classic example of an extraordinary circumstance both because there is absolutely no predictive basis and because the decisions are made entirely by others.
I'd be really surprised if an airline didn't have some sort of predictive model that estimates the risk of an ATC delay, especially when considering short to medium length delays (long and rare delays might be harder to do). Time of day, day of week, month of the year, and so on, probably give good clues as to the risk level. Dealing with these delays is an inherent part of running an airline and so there's nothing extraordinary about it.