Rescuers continue to scour a large area in the remote North Atlantic for a third day, racing against time to find a missing submersible 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 has the capacity to stay underwater for 96 hours, according to its specifications - giving the five people aboard until Thursday morning (local time) 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 1450km east of Cape Cod and 644km south of St John's, Newfoundland. United States and Canadian aircraft have searched more than 19,000 square kilometres, Captain Jamie Frederick told reporters 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 was also searching near the site, Frederick said.
"There is a full-court press effort to get equipment on scene as quickly as we can," he said.
Meanwhile, France will send a ship equipped with a deep-sea diving vessel to help the search-and-rescue operation, the government said on Tuesday. The Atalante is managed by the Ifremer research institute.
"It carries the Victor 6000 autonomous robot, capable of descending to a depth of 6000 metres, beyond the 3800 metres of the wreck's position", Ifremer said, adding the ship was expected to arrive on the site by Wednesday evening (local time).
Additional crew members from another ship are also being urgently dispatched to the search operation.
Those aboard the submersible, the highlight of a tourist expedition that costs $US250,000 ($NZ403,000) per person, included British billionaire Hamish Harding, 58, and Pakistani-born businessman Shahzada Dawood, 48, with his 19-year-old son Suleman, who are both British citizens.
A government source confirmed to Reuters that 77-year-old French explorer Paul-Henri Nargeolet is on board, while Stockton Rush, founder and chief executive of the vessel's US-based operating company OceanGate Expeditions, is reportedly with them as the pilot.
Challenging rescue
Rescuers face significant obstacles both in finding the Titan and in saving the people aboard, according to experts. The submersible is sealed with bolts from the outside, which means the occupants cannot escape without assistance even if it surfaces.
INHOSPITABLE TERRAIN
If the Titan is on the ocean floor, it would be nearly impossible to rescue, experts say, due to the extreme conditions 4km below the surface. The Titanic lies 12,500 feet (3810 metres) underwater, where light does not penetrate. Only specialised equipment can reach those depths without getting crushed by the massive water pressure.
The submersible lost contact about halfway down on its dive. "It's pitch black down there. It's freezing cold. The seabed is mud and it's undulating. You can't see your hand in front of your face," said Tim Maltin, an expert on the Titanic's sinking and wreckage.
BRING IT UP?
If the submersible is on the ocean floor, experts say that a sub-to-sub rescue is unlikely. Only a handful of submersible craft exist that could reach the depths of the Titanic wreck. Even if they could reach it, submersibles do not have the power to tow the missing vessel up to the surface.
If it's on the ocean floor, the number of unknowns is enormous. "We know more about the moon surface than the bottom of the ocean, because we just haven't surveyed it," said Jamie Pringle, a forensic geoscientist at Keele University in Britain.
FINDING IT ON THE SURFACE
If the vessel is bobbing at the ocean's surface, finding it will be a needle-in-a-haystack situation, experts say. The vessel the size of a van will be even harder to spot if it is partially submerged. It is far out in the ocean, so moving ships and equipment to the large area being searched takes time.
If the submersible experienced a mid-dive emergency, 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.
Safety issues
The ability of the tourist sub's hull design to withstand such depths was questioned in a 2018 lawsuit filed by OceanGate's former director of marine operations, David Lochridge, who said he was fired after he raised safety concerns about the vessel.
OceanGate said in its breach-of-contract suit against Lochridge, who is not an engineer, that he refused to accept the lead engineer's assurances and accused him of improperly sharing confidential information. The two sides settled their court case in November 2018.
Neither the company nor its lawyer, Thomas Gilman, immediately responded to requests from comment from Reuters.
An attorney for Lochridge declined to comment.
Several months before the suit was filed, a group of submersible industry leaders wrote a letter to OceanGate warning that the "experimental" approach" to the sub's development could result in "minor to catastrophic" problems, the New York Times reported.
US President Joe Biden is "watching events closely," White House national security adviser John Kirby said on Tuesday, adding that the US Navy is on standby to help if needed.
OceanGate said it was "mobilising all options," and US Coast Guard Rear Admiral John Mauger told NBC News the company is helping to guide the search efforts.
"They know that site better than anybody else," Mauger said. "We're working very closely with them to prioritise our underwater search efforts and get equipment there."
David Pogue, a CBS reporter, dove 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 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.
The sinking of the Titanic on 14 April 1912, which killed more than 1500 people, has been immortalized in books and films, including the 1997 blockbuster movie Titanic that renewed popular interest in the wreck. The huge ship had been on its maiden voyage.
Who is on board?
The British billionaire and chairman of aviation company Action Aviation is among those missing, according to his stepson. Dubai-based Harding had posted on social media that he was proud to be heading to the Titanic as a "mission specialist", adding: "Due to the worst winter in Newfoundland in 40 years, this mission is likely to be the first and only manned mission to the Titanic in 2023."
Harding was also on board the 2019 "One More Orbit" flight mission that set a record for the fastest circumnavigation of earth by aircraft over both geographic poles.
SHAHZADA DAWOOD and his son SULEMAN
Their family have confirmed they are on board. Shahzada is vice chairman of one of Pakistan's largest conglomerates, Engro Corporation, with investments in fertilisers, vehicle manufacturing, energy and digital technologies. According to the website of SETI, a California-based research institute of which he is a trustee, he lives in Britain with his wife and two children.
PAUL-HENRI NARGEOLET
The 77-year-old French explorer is director of underwater research at a company that owns the rights to the Titanic wreck. A former commander in the French Navy, he was both a deep diver and a mine sweeper. After retiring from the navy, he led the first recovery expedition to the Titanic in 1987 and is a leading authority on the wreck site. In a 2020 interview with France Bleu radio, he spoke of the dangers of deep diving, saying: "I am not afraid to die, I think it will happen one day."
STOCKTON RUSH
The founder and CEO of the vessel's US-based operating company OceanGate is also on the submersible, according to media reports. "It is an amazingly beautiful wreck," Rush told Britain's Sky news of the Titanic earlier this year. "Rush became the youngest jet transport rated pilot in the world when he obtained his DC-8 Type/Captain’s rating at the United Airlines Jet Training Institute in 1981 at the age of 19," according to his biography on OceanGate's website.