Dumb question: if planes descend, do they disappear off tracking? If so, why is this so? If the plane descends intact, why wouldn’t it be traceable? (I realize that if it is blown up, it would tend to “disappear.”
Again CNN assuming the plane made a landing and was ditched in the water... Ok, this guy did say that isn’t likely since there is no communication.
If the transponder is working you would, I believe, be able to track it all the way down depending upon how often it squawks. If the power is cut or there is some catastrophic failure (boom!) then probably not.