I've always heard IRR-ops (generally in the plural, even if only one flight is affected) from airline personnel. Never EYE-rops.

Maybe it's like IRR-ak or EYE-rak. IRR-ack (or irr-ACK) is correct, at least to Iraqis, but that doesn't stop lots of Yanks from saying EYE-rack. Might have something to do with what fits best with the overall speech patterns they're used to.