Beacon on the black box will only transmit for a limited time before the battery dies, and then you have to be fairly close to it's location if I understand it right.
*nod* I was trying for sarcasm (see odeon's comment above), then I heard on the news they thought they might be finding it via black box because the thing sends signals out (somehow I hadn't known that), and realized it actually wasn't an idiotic notion after all.