@onetrack
So far it seems the missile was launched 30km-35km away of the plane, when the BUK would have used it rocket fuel, it would still be more than 15km away. And there were clouds underneath the MH17. So, I would think it would need a little miracle to see the coming missile.
And the nearest plane was 30km away, above the MH17. After some 60 seconds of the missile explosion the plane flew roughly above the place where MH17 center body was going to hit the ground. If someone would be very carefully observing downwards from side windows, perhaps someone could have seen something in a distance of 5km+. Most likely also cockpit section had gone below clouds at that time.