This is an interesting article by David Cenciotti. He is a journalist with good knowledge on military aviation.
According to an authoritative source, two Su-27 Flankers escorted the Malaysian Boeing 777 minutes before it was hit by one or more missiles.
The Aviationist » ?All flights, including Malaysian B777, were being escorted by Ukrainian Su-27 Flanker jets over Eastern Ukraine?
A quote:
In other words: since the Russian interceptors had downed a Su-25 on the previous days, the Ukrainian escorted all military and civil flights over eastern Ukraine on Jul. 17. Including MH17.
Anyone who flew in this area ever noticed being escorted?