Friday, July 18, 08:20 PM GMT +0800 Media Statement 4 : MH17 Incident
MH17 filed a flight plan requesting to fly at 35,000ft throughout Ukrainian airspace. This is close to the ‘optimum’ altitude.
However, an aircraft’s altitude in flight is determined by air traffic control on the ground. Upon entering Ukrainian airspace, MH17 was instructed by Ukrainian air traffic control to fly at 33,000ft.
http://www.malaysiaairlines.com/my/en/site/mh17.html