As U.S. and Canadian planes and ships continued to search for signs of the submersible that disappeared on its descent to Titanic, one local expert said the chances of finding the Titan and rescuing its crew of five depend on a number of factors, time being the most important.

The submersible Titan went missing in the North Atlantic about 900 miles east of Cape Cod on Sunday. The five people aboard the Titan reportedly had enough oxygen to last up to 96 hours. That supply was down to 41 hours as of early Tuesday afternoon when the U.S. Coast Guard held a press conference on the search.

David Lovalvo, the president of the Mystic-based Global Foundation for Ocean Exploration who has spent decades designing and piloting deep water submersibles, said numerous things can go wrong when diving to depths where the water temperature is frigid and the pressure extreme. The wreck of the Titanic, discovered in 1985 by Lyme resident and ocean explorer Robert Ballard, sits on the bottom more than 12,000 feet below the surface. Ballard was on an expedition Tuesday and was unavailable for comment.

Lovalvo was an engineering consultant to the Woods Hole Oceanographic Institution and is certified to pilot the DSV Alvin, a deep ocean research submersible owned by the U.S. Navy. He said submersibles are typically designed with numerous safety features and undergo rigorous testing.

While some submersibles have a safety system like ballast weights that would allow it to simply rise to the surface in the event of an emergency, there’s always a chance Titan became snagged and unable to free itself, he said.

“The one thing that could happen is entrapment, especially when you’re diving around a wreck,” Lovalvo said. “She’s very deep. There are not many assets that can get to that depth. The ones that exist are spread around the world.”

In the event the Titan is on the bottom, Lovalvo said “they are counting on someone coming down.” The best chance for getting a vehicle down to the Titan is a remotely operated vehicle, which would be equipped with hydraulic manipulators or cutters and be able to free it up.

“That would be the best scenario, if they were just stuck,” he said.

If they are not stuck and simply unable to rise to the surface because of some other issue, Lovalvo said the rescue scenario gets more complicated and could involve something like a cable connected to the support ship and a winch to haul up the Titan.

But the Titan’s life support systems would be put to the test as time goes on, he said.

“Water temperatures at that depth are close to freezing. That can diminish your duration of life support. That’s a factor,” he said.

“They will eventually get it. But how fast they get it is the issue. The reason they’re doing such an extensive look at the surface is because there’s always a chance they surfaced away from the ship and are out there bobbing around,” he said.

“The bottom line is it’s not out of the realm of possibility that they are just down there waiting for help. There is still a chance this could have a happy ending,” he said. “A positive outcome is what is on everybody’s mind. We’re just not going to know until they get underwater and see.“

The Titan was on a mission conducted by the private company OceanGate Expeditions. It’s support ship Polar Prince lost contact with the Titan 1 hour and 45 minutes into its two-hour descent to the Titanic. Those on board include a pilot and four “mission specialists,” including OceanGate CEO and founder Stockton Rush.

Published reports show the crew includes British billionaire Hamish Harding and Pakastani businessman Shahzada Dawood and his son, Suleman.

The search included an area of about 10,000 square miles, the U.S. Coast Guard said. The search includes aircraft, boats, radar equipment and sonar buoys able to detect sounds below the surface.

An underwater rescue at the depth of the Titanic, has never been attempted. The deepest ever underwater rescue came in 1973 when two men, Roger Chapman and Roger Mallinson, aboard the Pisces III, were rescued at a depth of 1,575 feet after being trapped for 76 hours.

Retired Navy Capt. Paul Whitescarver, former commanding officer at the U.S. Naval Submarine Base in Groton, said the Navy participates in the International Submarine Escape and Rescue Liaison Office, which facilitates an international response to submarines in distress. But while the group maintains submersible vessels designed to rapidly respond to downed submarines, those submersibles can reach about 2,000 feet, deeper than submarines, but not even close to the depths of the Titanic, he said.

The vessels used in submarine rescues are also specially designed to mate with the submarine to transfer crew out of the submarine.

The Navy released a statement on Tuesday, indicating it was sending personnel and a Flyaway Deep Ocean Salvage System, “a motion-compensated lift system designed to provide reliable deep ocean lifting capacity for the recovery of large, bulky, and heavy undersea objects such as aircraft or small vessels.” The equipment and personnel would support the Coast Guard and expected to arrive in St. John’s, Newfoundland on Tuesday evening.