The link to the main BBC Website story of 17th July 2014 before MH-17 was hit.
It is all about Kiev claiming that Russian aircraft crossing the border and attacking Ukrainian aircraft directly and includes a puff piece from Daniel Sandford about what an escalation this would be if true.
In short (and stated previously on these boards) With Kiev high command telling everybody (including its front line forces) that the Russian Airforce was attacking them directly, this would have been the day that pro Kiev forces switched on their full Air Defence capability in earnest.
The rebels also had AD weapons but they had been using them for weeks already.
The new comers were the Pro Kiev side and within hours an Airliner was downed.