... Commander William Marks from the US Seventh Fleet, which is taking part in the search, says he expects the plane's flight recorders to be floating in the water.
"In calm seas, if there were a soccer ball [football] or a basketball floating in the water, the radar could pick it up. They [flight recorders] typically have a radio beacon and so for example our P3 [radar] - if they are flying within a certain range of that - will pick up that radio beacon. We have not yet picked up anything, but that's typically what those black boxes contain." ...
The sentence in bold letters, is incorrect, as far as my knowledge is concerned.
Well, if they would be at the surface. But the CVR/FDR does not float if they are stuck in the fuese of the plane which sinks to ground.
Underwater the P-3 only would pick up the sound if they would deploy the sonnar buoy.
Thinking on the size of the area - if you actually have no bloody idea of where to deploy the buoy, it would be almost impossible to pickup the signal.
Remember, AF447, the signal was captured by a submarine on its sonnar!