Missing an operation OCCASIONALLY isnt a big deal. Mind you there is 2 FTX/OPs a month so missing one a month may become an issue. But one every 3 or 4 months IMO wouldnt be trouble.
Yea and what Stewart said, make sure you let your FTL know.
As long as it is only occasionally and you let your COC know, it should be of no issue. The issue derives in people failing to show up with no forward word or word at all.