In this photo released by Action Aviation, the submersible Titan is prepared for a dive into a remote area of the Atlantic Ocean on an expedition to the Titanic on Sunday, June 18, 2023. Rescuers raced against time Tuesday, June 20, to find the missing submersible carrying five people, who were reported overdue Sunday night. (Action Aviation via AP)

BOSTON (AP) — Time is quickly running out in the search for a missing submersible that lost contact with its mother ship on Sunday as it descended to the wreck of the Titanic with five people aboard.

As an international fleet of surveillance vessels and aircraft forges ahead with ongoing search and rescue efforts, each passing second makes it less likely that the passengers on the Titan will be found alive as their oxygen supply is expected to run out by this morning.

Even if the Titan is located in the North Atlantic, it could be nearly impossible to reach if it is stuck on the ocean floor at roughly 12,500 feet near the Titanic’s wreckage.

The five people on board are pilot Stockton Rush, the CEO of OceanGate, the company leading the expedition; British adventurer Hamish Harding; Shahzada and Suleman Dawood, a father and son from a prominent Pakistani family; and French undersea explorer and Titanic expert Paul-Henry Nargeolet.

There are several possible outcomes for the Titan and its passengers.

TITAN FOUND ON SURFACE

The Titan has built-in safety systems that help it rise to the surface in case of emergency including sandbags and lead pipes that can be released, as well as an inflatable balloon. The system was designed to work even if everyone on board is unconscious.

That would be the best case scenario, but even then there would not necessarily be any survivors, said Lawrence Brennan, a professor at Fordham University’s School of Law.

VESSEL FOUND INTACT ON OCEAN FLOOR — NO SURVIVORS

If the Titan is stuck on the ocean floor the occupants would eventually run out of oxygen and develop hypothermia from extreme cold, according to experts.

Nargeolet, who has made more than 30 trips to the Titanic’s wreckage, explained to the Titanic Channel in a 2019 interview the possible dangers of being trapped in another submersible, called the Nautile, in the deep ocean.

There is enough oxygen for four or five days, but that’s no help because it’s unlikely help will arrive in that time, he said. The biggest issue at the ocean floor is the water temperature of roughly 33 degrees.

ENTANGLEMENT

Getting stuck in ropes, lines or nets is another possibility.

There’s a lot of old fishing rope in the ocean and there is danger of entanglement from the Titanic’s ropes or cables, said Greg Stone, a California-based ocean scientist who has been on similar submersibles.

In that case, the mother ship should have had a remotely operated submersible vehicle with cutters that could descend and cut the lines, Stone said.

Mission pilot Rush was aware of entanglement dangers.

“What I worry about most are things that will stop me from being able to get to the surface — overhangs, fish nets, entanglement hazard,” he said in an interview with CBS News last year.

VESSEL FOUND INTACT WITH SURVIVORS

A Canadian military surveillance aircraft detected underwater noises in the area of the Titanic wreck, which might indicate that at least someone is alive on the Titan and trying to signal for help.

The U.S. Coast Guard said they couldn’t say what was making the noises but they are searching the area where they were detected.

The noises are encouraging because submarine crews unable to communicate with the surface are taught to bang on their hull to be detected by sonar.

The problem in that scenario is finding another vessel that can go deep enough for a rescue.

The best chance to reach the submersible could be to use a remotely operated robot on a fiber optic cable, said Jeff Karson, a professor emeritus of earth and environmental sciences at Syracuse University.

HULL BREACH

A breach of the Titan’s hull at depth would mean instant death from the heavy pressure in the deep ocean.

The water pressure 12,500 feet below the surface at the site of the Titanic wreck is roughly 400 atmospheres or 6,000 PSI.

CBS News journalist David Pogue said the vessel’s two communications systems stopped working about an hour and 45 minutes after the Titan submerged on Sunday.

“There are only two things that could mean. Either they lost all power or the ship developed a hull breach and it imploded instantly. Both of those are devastatingly hopeless,” Pogue told the Canadian CBC network on Tuesday.

NO HOPE OF SURVIVAL

Even when there is no hope of any occupants surviving because their oxygen is depleted, recovery of the vessel will be difficult.

One of the problems with locating the submersible could be that debris from the Titanic is spread out over a kilometer and some could be as big as the submersible itself, Karson said.

The submersible is essentially “another lump down there,” he said.