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Wreckage has been sighted, but NOT confirmed to be from the missing plane.
Terrorism is begining to look likely IMHO. Even the most sudden mechanical failure or bird strike or extreme weather, generally allows time for a plane to glide for some minutes at least and transmit a distress signal.
Even if the plane is subsequently lost with all on board, there would still be a record of the distress call, and some idea of the crash site.

Very sudden disaster without time for a Mayday call does perhaps suggest a bomb, shoot out, or a highjacking by someone not competant to fly the plane.

I am afraid that I now see no hope for those on board. Historicly there have been cases of survivors of air crashes being discovered long afterwards in remote places, but with modern locating beacons etc this seems unlikely in the modern world.