I imagine you're referring to situational irony, but there are a few more literary ways to use it. Ignoring that, it really isn't hard to see how it is ironic that they planned to do today anyways, but instead of everything going smoothly, there was a severe unseen outage that they weren't prepared for.
When the whole trend of "irony has only one meaning" start? Every dictionary I've looked at includes something like "incongruity between the actual result of a sequence of events and the normal or expected result" (I've got an old Webster's New World from the 40's that gives the example "it was an irony of fate that the fireboat burned and sank, which is exactly the kind of thing that a certain type of person claims is "coincidence, not irony").
Sorry, I don't mean to be a pedantic jackass, but still I said it.