I’m not buying the engine fire causes plane to crash explanation being given the media.  The Boeing 737-800 is highly reliable with sophisticated fire detection and fire suppression systems.  Also, this particular aircraft is only three years old.  An engine fire would not cause a loss of control of the aircraft unless an explosion would rupture the firewall between the engine itself and the wing structure.  The fire suppression systems on the 737 includes fuel and air shutoffs AND onboard fire extinguishers.  And the plane is designed to be flyable on one engine, which should have allowed it to return safely to Tehran or other nearby airport.

Watching the video, the plane was on fire all the way to the ground, which tells me that it was a serious explosion on board that got around the fire containment design.  This is very suspicious and I’m suspecting onboard sabotage or a shootdown.  Know what was going on at the time, I won’t be a bit surprised that Iran’s own anti-aircraft defense systems shot this one down.