Can anyone confirm whether all airliners now have crash activated ELTs? Or whether just newer ones do, and the older ones just have ELTs in the cabin / rafts for manual activation?
At least in FAA land ELT's are required and have been as long as I can remember (
http://www.ntsb.gov/news/events/2012...ions/Smith.pdf)
They are activated (theoretically) by a G switch and/or cockpit remote switch (I don't recall seeing one in an airliner but I haven't spent much time up the pointy end of those). They don't (just like all normal radio) transmit from underwater even if it was activated.
As for debris from mid-air explosion, I'd be looking for something a-la TWA800
TWA Flight 800 disaster - a look back - Photo 16 - Pictures - CBS News in the water if it came apart in mid-air. Apparently they have nothing of the sort in the area they've been looking at.