@Janine: The recording of the CVR & FDR can not be disabled. If you have meant the transponder, I completely agree with you. I don't find any reason why there is a provision kept for someone in the cockpit to be able to turn the transponder off for the comercial flights. I was under the impression that the transponder cannot be turned off the same way as the recording by CVR & FDR but I was surprised to learn that it could be turned off by the pilot or anybody in the cockpit who is educated about it.
I believe the speculation around the unlucky flight MH370 and its Human Beings load, has overpassed any tolerable assumption of what is credible and what is just pure fantasy, but the question is more technical and refers to the technology inside an aircraft, so we know superficially that computers have the main role, and said computers because there are few redundants or in other words, if one fails there's its twin taking over the reins of governing the air giant, there are black boxes, OK, but WHY a giant of the air gets lost ????? Is it too far from aviation engineering to provide an electronic system maybe based on GPS system, to transmit position data that cannot be deactivated by anybody either pilots or cabin crew.... ?????
The black box (flight data recorder) is not the same thing as the radar ID transponder. The transponder sends the identifying data (I believe the military version is called Friend-or-Foe) that associates the plane ID with the radar blip---without it, all the radar sees is a reflection that could be anything: a balloon, a flock of birds, etc.
It is possible to turn off the transponder---it happened both on flight 370 and during the 9/11 event. I don't think it's possible to turn off the FDR, but the data is not available until they find the actual box, which of course has not happened yet in this case.