Rescuers were scouring thousands of square miles in the remote North Atlantic on Tuesday, racing against time to find a missing submersible two days after it disappeared while taking wealthy tourists to see the wreckage of the Titanic in deep waters off Canada's coast.
The 21-foot Titan submersible has the capacity to stay underwater for 96 hours, according to its specifications - giving the five people aboard until early on Thursday before air runs out. One pilot and four passengers were inside the submersible early on Sunday when it lost communication with a ship on the surface about an hour and 45 minutes into its dive.
The Titanic site is about 900 miles (1,450 km) east of Cape Cod and 400 miles (644 km) south of St. John's, Newfoundland. US and Canadian aircraft have searched about 7,600 square miles, larger than the state of Connecticut, Captain Jamie Frederick told reporters at a press conference on Tuesday.
The Canadian military has dropped sonar buoys to listen for any sounds that might be coming from the Titan, with no results thus far. A commercial vessel with an unmanned vehicle capable of deep dives is also assisting, Frederick said.
"There is a full press full-court press effort to get equipment on scene as quickly as we can," he said.
Those aboard the submersible, the highlight of a tourist expedition that costs $250,000 per person, included British billionaire Hamish Harding, 58, and Pakistani-born businessman Shahzada Dawood, 48, with his 19-year-old son Suleman, both British citizens.
The 77-year-old French explorer Paul-Henri Nargeolet and Stockton Rush, founder and CEO of the vessel's US-based operating company OceanGate, were also reported to be on board. Authorities have not confirmed the identity of any passenger.
Rescuers face significant obstacles both in finding the Titan and in saving the people aboard, according to experts.
If the submersible experienced an emergency in mid-dive, the pilot would likely have released weights to float back to the surface, according to Alistair Greig, a professor of marine engineering at University College London. But absent communication, locating a van-sized submersible in the vast Atlantic could prove challenging, he said.
The submersible is sealed with bolts from the outside, which means the occupants cannot escape without assistance even if it surfaces.
If the Titan is on the ocean floor, a rescue effort would be even more challenging due to the extreme conditions more than two miles below the surface. The Titanic lies 12,500 feet (3,810 meters) underwater, where light does not penetrate. Only specialized equipment can reach those depths without getting crushed by the massive water pressure.
"It's really a bit like being an astronaut going into space," said Tim Matlin, a Titanic expert. "I think if it's on the seabed, there are so few submarines that are capable of going that deep. And so, therefore, I think it was going to be almost impossible to effect a sub-to-sub rescue."
OceanGate said it was "mobilizing all options" to rescue those aboard the Titan. US Coast Guard Rear Admiral John Mauger told NBC News the company is leading the search efforts with Coast Guard assets brought to the site.
"They know that site better than anybody else," Mauger said. "We're working very closely with them to prioritize our underwater search efforts and get equipment there."
Billionaires aboard the missing submarine
OceanGate schedules five week-long "missions" to the Titanic each summer, according to its website.
David Pogue, a CBS reporter, dove to the site on board the Titan last year. In a December news report, he read aloud the waiver he had to sign, which noted the submersible had "not been approved or certified by any regulatory body" and could result in death.
In an interview on Tuesday, Pogue said the OceanGate has successfully gone down to the wreck around two dozen times and that the company does a meticulous safety check before each attempt.
"They treat this thing like a space launch," he said. "It is definitely a culture of safety."
Harding, a UAE-based businessman and adventurer who is chairman of Action Aviation, posted a message on Facebook on Saturday, saying: "This mission is likely to be the first and only manned mission to the Titanic in 2023."
Fellow tourist Dawood is vice chairman of Engro, one of Pakistan's largest conglomerates with investments ranging from fertilizers and energy to vehicle manufacturing.
The sinking of the Titanic, which killed more than 1,500 people, has been immortalized in books and films, including the 1997 blockbuster movie "Titanic" that renewed popular interest in the wreck.