The crew races against time and terrifying conditions aboard the lost tourist submarine Titanic

HALIFAX, Nova Scotia — Gio Benitez of “GMA” reports from Halifax, Nova Scotia about the desperate search for five missing people aboard a tourist submarine inspecting the wreckage of the Titanic.

A Canadian plane did take a banging sound over sonarbut the first time it was detected was more than a day ago.

A United States Coast Guard search of the area turned up nothing.

The United States, Canada and France are all involved in the search for the missing submarine.

The crew is looking underwater but also above water because in case of an emergency, submarines are designed to surface and float on the water.

But the submarine has not yet been sighted.

Even if the submarine makes it to the top, the occupants cannot get out. They are locked and bolted from the outside.

Submarines have less than 24 hours of oxygen left on board.

If they are underwater, underwater is very dark.

In order to survive, they must be very quiet and asleep in order for them to conserve oxygen.

If they emit too much carbon dioxide in a panic, it can also poison the air.