Apologies for pulling this thread slightly to one side, but has thought ever been given to the possibility of giving the FDR a flotation capability, perhaps with an attached gas bottle and inflatable bag?
In the case of a landing on hard ground and/or fire, these attachments would be broken off or destroyed without affecting the FDR's survival, but in the present AF situation with the aircraft structure apparently breaking up before or on contact with the sea the flotation ability might bring the FDR to the surface for rapid recovery.