Mid Air?
Unannounced / unidentified military activity is not unheard of in this area.
For an established proven commercial aircraft to completely disappear without any indication, points to some sort of catastrophic instantaneous failure/ breakup.
That would indicate explosive, structural or midair.
Beyond that we just cant say.
Some of the drivel spouted here would be quite humorous if the situation was not so tragic.
The media frenzy of speculation, theories and fantasy is thoroughly distasteful but sadly a reflection on humanity (or rather lack of it)
I'm sure all will out eventually.