(inspired by a question on reddit, I’ll post a reply too)
Short answer: ocean is very big, submersible is very small.
Long answer: Imagine going out on a football pitch with a white paint marker. Randomly walk around and pick a single blade of grass to paint white. Now grab someone that didn’t observe you and tell them to find the painted blade of grass. Also tell them they have a limited time, and that you might have pushed the blade of grass doen into the ground.
There has to be a solution that would have allowed them to send a buoy up to transmit a mayday and coordinates like some life boats do. This would help the rescue teams to narrow the search grid. I wouldn’t have gone down in that thing, but if I WAS, I would at least feel better with something like that.
A beacon should work as I described in a separate response. A buoy could work too, but the buoy a) would need to be designed to float up from 4 km and still be functional at the surface b) the sub doesn’t necessarily know where it is below the ocean. GPS doesn’t work down there!
