c. A literary style employing such contrasts for humorous or rhetorical effect.
2.
a. Incongruity between what might be expected and what actually occurs:
Humour doesn't enter into this. No connection - you're applying the wrong definition.
The quote above indicates just two of several types of irony, and the first, the literary style, is clearly not relevant here. Helicopter accidents are nothing whatsoever to do with literary style - what a bizarre suggestion!
The second defiition however is the one that does apply; the apparent incongruity between safety inspectors going flying and then having an accident. You wouldn't question the irony of a health and safety herbert falling off his doorstep, would you?
ie a perfectly logical, accurate and acceptable use of the word "ironic".