As time runs out for the Titan sub crew, search and rescue experts explain what happens next

Despite the final stores of oxygen aboard the missing Titan submersible due to run out Thursday morning, the monumental effort to rescue its five passengers continues unabated.

Aircraft fitted with sonar, various sea vessels and deep sea exploration tools have been deployed in an effort coordinated by the US, Canada, France and others to find the OceanGate Expeditions’ submersible — which disappeared just an hour and 45 minutes into its Titanic exploration off the coast of Newfoundland on Sunday with air reserves of 96 hours.

Frank Owen, a former submarine officer with the Royal Australian Navy and search and rescue expert, stressed rescuers will continue to search with “a huge amount of urgency” and will certainly “go long beyond 96 hours,” which were estimated to end Thursday at roughly 7 a.m. EST.

Reports of recurring “underwater noises” characterized as both “banging” and “tapping” spurred hope Wednesday, the search-and-rescue mission’s third day.

“This is a search and rescue mission, 100%,” First Coast Guard District Captain Jamie Frederick told reporters Wednesday. “We’ll continue to put every available asset that we have in an effort to find the Titan and the crew members.”

Aboard the ship were OceanGate founder and CEO Stockton Rush, Titanic specialist Paul-Henri Nargeolet, UK billionaire explorer Hamish Harding and Pakistani billionaire and mogul Shanzada Dawood and his 19-year-old son, Sulaiman. They are sealed into the sub by 17 bolds, which can only be opened from the outside.

The looming loss of breathable air also raises the question of what happens next?

Butch Hendrick, a longtime diver who teaches water rescue procedures, told The Post he did not expect officials to begin to change the mission from a rescue effort to a recovery effort — the difference being the belief that the victims would still be alive — until at least 24 hours after the estimated oxygen reserve has expired.

“At that point,” he said, “they’ll start to make decisions that, ‘Yes … we have done the best we can and it’s time to go to another level of search.’”

Hendrick, president and founder of US-based public safety dive training company Lifeguard Systems, said recovery missions typically involve a slower search process with less manpower and fewer resources.

“But they will still have major vessels and equipment,” he added.

Searchers have been scouring waters up to two and a half miles deep, spanning an area two times as large as Connecticut.

The Coast Guard has called in as many ships, airplanes and other equipment — such as undersea technology to scan for additional noises — to aid in the search and rescue mission.

Hendrick and Owen both questioned the amount of oxygen that was estimated to have been left.

Hendrick noted how OceanGate never tested for the full 96 hours, and “it was never tested under stress of five persons in it.”

“It’s very difficult to say, ‘We have X amount of hours left,’” he added.

But Owen said the 96 hour limit could be extended “if the people on board have managed to conserve their oxygen by breathing slowly and sleeping.”

Locating the Titan submersible is the first hurdle — then comes the question of how to get it to the surface.

The submersible is said to have the ability to “self-surface,” a mechanism that allows the vessel to rise to the surface in the event of an emergency.

There has so far been no sign of the submersible along the surface.

“If it can’t do that, it suggests that it’s either entangled, right?” Owen surmised. Or “it’s got extra weight on board,” such as water.

Searchers have brought in the Victor 6000 remotely operated vehicle (ROV) to search for the sub within the remains of the Titanic and, if stuck, try to help it dislodge from whatever might have it caught.

It is also hoping to attach a winch from a support ship to the sub, which could then bring it to the surface, although that could also create problems.

“You’re lifting with a winch that is probably on the same ship as [another] winch that is providing the umbilical to the remotely operated vehicle.”

The ROV could also carry, for example, a bladder of fuel to the submersible using an anchor, and then attach the container to the vessel, release the anchor and give the sub the buoyancy it needs to float, Owen said.

But it’s “a lengthy process,” he went on.  “It’s a salvage job rather than a recovery rescue.”

Owen added: “We would hope that that’s not the case, and everybody will be fighting hard, as hard as they can.”