From the very beginning the notion that a ‘technical problem’ could cause a modern airliner to fall from the sky in pieces seemed the least likely of potential causes of the horrific and tragic Russian air disaster. One cannot imagine the anguish of relatives whose loved ones are suddenly gone. One can see why both the Russians and the Egyptians were so reluctant to admit that terrorism could be the cause. The Egyptian tourism industry is in enough trouble from the fear of terrorist attacks; an aircraft brought down flying from a supposed safe area still frequented by tourists would be very difficult to cope with. The Russians are now engaged in Syria and President Putin has widespread support at home for his policy, but terrorist outrages which kill innocent civilians in retaliation may weaken that.
Nevertheless there are now only two likely causes. Terrorism via a bomb on board or a missile fired from the ground. Or an exploding engine which ripped the fuselage and caused the plane to break up; even with that a systems failure really does seem unlikely, although not impossible. An engine might have been sabotaged, which could be an easier terror option than getting a bomb aboard. We should not have long to wait for the answer.
Whatever it is can little help the grief for those whose lives have been lost. But it will have wide implications. It no longer seems right to allow civilian airliners to fly over conflict zones and regions bordered by failed states. There is this theory that at a certain height the plane is safe from ground to air missiles, but that is no longer certain and the risk is too great.