The plane just disappeared from radar at 37,000 ft. No descent data. It’s there then it’s gone. This suggests a breakup of the aircraft at altitude. Mechanical fault or bomb?
The plane was coming and going from Paris. Terrorism? A time bomb could have been placed in a well hidden place while it was in Eritrea or Tunisia, set to go off hours and several flights later. Who knows?
There s no way a modern airliner just comes apart in midair. If the airplane is squawking one second and not the next, it’s a pretty safe bet it exploded.
There are back up systems that will still work during a catastrophe, like a steep dive for the deck or a structural failure.