[Skybird]

Me too thinks a terror strike is the most likely scenario, for two reasons.

First, if there is no distress call that got sent, whatever happened must have happened very fast. Engine fires and malfunctions usually do not lead that quickly to penultimate desaster that pilot and copilt cannot even release an emergency call. Which leaves some kind of explosive decompression as the top explanation.

Second, we are approaching summer holidays slowly but surely, and a major international sports event. And Muslim terror is locked in a fight with the Egyptian state for which tourism is a major source of income. Any attack reducing that income, is a blow to the Egyptian state.

Also there already have been attempted and successful attacks on airliners in Egypt recently.

From a Muslim terrorists POV , the chosen target makes sense. Plus revenge for Mursi and the MB, and all that.

Russian FSB also claims it to be a terror strike, but gives no evidence.

Other scenarios are possible explanations as well at this point of time. But the terror theory has the highest realistic probability of all possible scenarios one could imagine, currently. And the aircraft model, an A320, has a remarkable technical reliability record.