“Sure it is possible. But hasn’t it been flying fine for 14 years with the repair it received?”
Yes, but that is exactly what you would expect with that kind of a stress fracture in a monolithic structure. Aluminum aircraft, commercial and military, are rebuilt and/or retired after so many cycles and flight hours to avoid undetected metal fatigue failures from occurring in flight. In cases such as the novel wings of the TU-144 or the latest composite material aircraft, the engineering assumptions have not yet had sufficient time to reveal whether or not the forecast assumptions about composite material fatigue are fully reliable or not. See what happened with the de Havilland Comet air disasters and how their engineering assumptions about metal fatigue proved to have fatal flaws. Also look at what happened to a 131st Tactical Fighter Wing F-15 when it prematurely cracked and broke apart in mid-air, grounding the fleet of F-15 aircraft. My test pilot uncle and his crew were killed during World War Two when a aircraft manufacturer failed to understand and recognize the metal fatigue in his patrol bomber aircraft caused it to disintegrate during testing over the bombing range.
Certainly it is possible. The reason I doubt it is because of the timing and location. Russia did not start bombing ISIS that long ago. ISIS only recently called for attacks on Russians. So sure, it certainly could be that it was worn out metal. I do not think ISIS is that lucky. They are evil. If it was an accident, they are evil enough to immediately take credit. I don’t know. They are evil enough to take the credit when it is not due. My money is on the premise that they actually had something to do with it.
There was another plane that went down a while back where they took credit and everyone said “I don’t know I don’t know...” until the pilot ended up on one of their snuff films. I don’t remember the details. Do you?
Apparently we denied they shot that one down, too.
http://www.bbc.com/news/world-middle-east-30600500
With NDI inspections, there is not much of a risk for undetected stress fractures/failures.
“Also look at what happened to a 131st Tactical Fighter Wing F-15 when it prematurely cracked and broke apart in mid-air, grounding the fleet of F-15 aircraft.”
The portion of the canopy rail that failed was not subject to NDI inspections that would have caught it. The canopy rails were over-built and all that BUT that rail was somehow thinner than all the other rails in the F-15 fleet—hence the failure.