We saw that when Claire was trying to sign the adoption papers, her pens failed to work in the same way that Mike's gun didn't work for him at multiple attempts. So come on Powers That Be, when are you going to tell us why the island wouldn't let Claire take Aaron anywhere but to the island? The psychic said that it would have to be that flight. So it looks as if the island was calling the shots there. I hope that we don't have to wait until the finale of all finales, to learn why Aaron was supposed to crash on the island (and, exactly how it is that the island has all this power to control events!). But it's such a huge mystery at this point, that's probably when and how it will be revealed...in the final scene before the blackout-boom-logo. At least maybe TPTB will give us a few hints and crumbs along the way.
Some theories on Aaron can of course be found at Lostpedia. One that sounded interesting to me was: "Jack and Kate are the "nice couple in LA" to whom Richard Malkin wanted Claire to give Aaron. He didn't know that the plane would crash, but only knew of the future where Jack and Kate were happily raising Aaron." That makes it appear that although Malkin was perhaps not an operating psychic, maybe he did get flashes of precognition like Desmond that didn't really fit together, and he just pieced them in his head to make as much sense of them as he could. Hmmm.