"An Irish Airman Foresees His Death"—seems simple enough, don't it? It tells us that the poem will be the meditation of an Irish airman (pilot) who foresees his own death. And… that's what we get, for the most part. The speaker doesn't really foresee the exact circumstances of his death, but that's no mater. He knows he will die. But there's more to the title than just this.
First, notice that it says "An Irish Airman" and not "The Irish Airman" or "Bill O'Keefe sees his death." The title names a generic Irish pilot, not any specific one (even though Yeats had a very specific one in mind, one Major Robert Gregory). The "an" is important because it could refer to any number of Irish pilots. The speaker's eventual fate isn't just his own, but, potentially, that of any number of other guys. This is Yeats' way of speaking for the Irish pilots as a whole, not just the one that he knew.
The other thing about the title is that it seems really matter-of-fact. It reminds us of some emotion-less newspaper headline, a blurb in a long list of facts. There's no hint of sadness or tragedy, no vociferous anti-war protesting, no comments on the absurdity of the airman's death, nothing. Nada.
This is not to say that Yeats didn't care, but rather that he cared in a different way. The title sarcastically or ironically imitates the ways in which the death of soldiers was, and often is, reduced to just a flat statement that says nothing about who the soldier was, how sad his death was, or anything: "so-and-so foresaw his death; so-and-so was shot down." War is bad, and the way a soldier's death is sometimes handled is just as bad, as the title lets us know.