An aircraft heard sounds at 30-minute intervals from the area where the sub disappeared, according to internal e-mails sent to DHS leadership obtained by Rolling Stone
An aircraft heard sounds at 30-minute intervals from the area where the sub disappeared, according to internal e-mails sent to DHS leadership obtained by Rolling Stone
Man this sounds terrible. But the banging noises will probably stop some time today. The 4 days of oxygen will end very soon.
I'd say it's unlikely they would make banging noises if they were somewhere on the surface, waiting to be found. It's more of a thing if you're stuck underwater and cannot use flare gun, radio or similar equipment.
A few days ago an article explained there are lots of structures around the wreck where such a submarine could get stuck. That would also explain why the sub is not at the surface, as they can just drop weights and it will automatically emerge to the surface.
They can't use a flare gun or even leave the submersible because they were sealed in from the outside. They are likely on the surface because the banging was picked up by buoys, but the search area is so large that it's unlikely they'll be found. Also the banging is part of the search and rescue process as they bang every half hour.