Crashes are pretty rare. You would need to stream all the black box data of all planes all the time in order to catch the few instances where you actually have a crash.
That’s a lot of constant network traffic to deal with for not a lot of instances where you need it.
On top of that you would *still* have to consider the scenario that there’s a technical problem with transmission immediately before the accident, in which case you’ll want the black box as a backup anyway.
It’s also important to note that searching for the black box isn’t a huge effort on top of the normal crash response and investigation. A lot of responders or search vehicles are going into that area anyway to search for survivors, dead people, wreckage, clues… and the black box. Even if you had all the data streamed to you, you’d still be doing most of that.
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