Basic trigonometry will tell you that the apparent size, elevation and speed of a high-altitude airliner and a lower-altitude turboprop are virtually indistinguishable from the ground. That's before you throw in cloud cover, sun position, distances involved, and the fact that MH17 was approaching head-on, all of which blur the ability to tell one from the other.
Basic trigonometry immediately tells you the altitude if you know the angle and distance (the two parameters Buk operator always sees).
Last edited by ASIP; 9th Aug 2014 at 00:52.