BOSTON (AP) — A renowned Titanic expert, a world-record holding adventurer, two members of one of Pakistan’s wealthiest families and the CEO of the company leading an expedition to the world’s most famous shipwreck are facing critical danger aboard a small submersible that went missing in the Atlantic Ocean.

The submersible Titan was reported overdue Sunday night about 435 miles (700 kilometers) south of St. John’s, Newfoundland, according to Canada’s Joint Rescue Coordination Center, spurring a desperate international rescue effort. Rescuers were racing against the clock because the oxygen supply could run out by approximately 6 a.m. Thursday.

A Canadian aircraft detected underwater noises during the hunt for the Titan. The U.S. Coast Guard said via Twitter early Wednesday that as a result of the noises detected by the Canadian P-3 patrol aircraft, search efforts have been relocated and the data is being used to help guide the ongoing effort.

The expedition featuring the Titan was led by OceanGate, making its third voyage to the Titanic, which struck an iceberg and sank in 1912, killing all but about 700 of the roughly 2,200 passengers and crew.

A pilot and four other people are on the Titan. They are:

STOCKTON RUSH

Although his background is in aerospace and technology, Rush founded OceanGate Inc. in 2009 to provide crewed submersibles for undersea researchers and explorers, according to the company’s website. Rush is the Titan’s pilot, said company spokesperson Andrew Von Kerens.

The private company based in Washington started bringing tourists to the Titanic in 2021 as part of its effort to chronicle the slow deterioration of the wreck.

“The ocean is taking this thing, and we need to document it before it all disappears or becomes unrecognizable,” Rush told The Associated Press in 2021.

In an interview with CBS News last year, Rush defended the safety of his submersible but said nothing is without risk.

“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, adding that a good pilot can avoid such perils.

Rush became the youngest jet transport rated pilot in the world at age 19 in 1981, and flew commercial jets in college, according to his company biography. He joined the McDonnell Douglas Corp. in 1984 as a flight test engineer. Over the past 20 years, he has overseen the development of multiple successful IP ventures.

Greg Stone, a longtime ocean scientist and a friend of Rush, called him “a real pioneer” in the innovation of submersibles.

“Stockton was a risk-taker. He was smart. He was, he had a vision, he wanted to push things forward,” Stone said Tuesday.

HAMISH HARDING

A British businessman, Harding lives in Dubai in the United Arab Emirates. Action Aviation, an aircraft brokering company for which Harding serves as chairman, said he was one of the mission specialists, who paid to go on the expedition.

Harding is a billionaire adventurer who holds three Guinness World Records, including the longest duration at full ocean depth by a crewed vessel. In March 2021, he and ocean explorer Victor Vescovo dived to the lowest depth of the Mariana Trench. In June 2022, he went into space on Blue Origin’s New Shepard rocket.

“Both the Harding family and the team at Action Aviation are very grateful for all the kind messages of concern and support from our friends and colleagues,” the company said in a statement.

In a Facebook post Saturday, Harding said he was “proud” to be part of the mission.

“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,” he posted. “A weather window has just opened up and we are going to attempt a dive (Sunday).”

Harding was “looking forward to conducting research” at the Titanic site, said Richard Garriott de Cayeux, the president of The Explorers Club, a group to which Harding belonged.

“We all join in the fervent hope that the submersible is located as quickly as possible,” he said in a statement.

SHAHZADA AND SULEMAN DAWOOD

Father-and-son Shahzada and Suleman Dawood are members of one of Pakistan’s most prominent families. Their family said in a statement that they were both aboard the vessel.

“We are very grateful for the concern being shown by our colleagues and friends and would like to request everyone to pray for their safety while granting the family privacy at this time,” the statement said. “The family is well looked after and are praying to Allah for the safe return of their family members.”

Their firm, Dawood Hercules Corp., based in Karachi, is involved in agriculture, petrochemicals and telecommunication infrastructure.

Shahzada Dawood also is on the board of trustees for the California-based SETI Institute that searches for extraterrestrial intelligence. The Dawoods live in the UK, according to SETI.

Shahzada Dawood is also a member of the Global Advisory Board at the Prince’s Trust International, founded by Britain’s King Charles III to address youth unemployment.

He has degrees from the University of Buckingham in the United Kingdom and Philadelphia University (now Thomas Jefferson University) in the U.S.

PAUL-HENRY NARGEOLET

Nargeolet is a former French navy officer who is considered a Titanic expert after making multiple trips to the wreckage over several decades.

David Gallo, a senior adviser for strategic initiatives and special projects at RMS Titanic, said in an interview with CNN that Nargeolet was on board.

He is director of underwater research for E/M Group and RMS Titanic Inc., has completed 37 dives to the wreck and supervised the recovery of 5,000 artifacts, according to his company profile.

He was expedition leader on the most technologically advanced dive to Titanic in 2010, which used high-resolution sonar and 3D optical imaging on the bow and stern sections as well as the debris field.

While with the French Institute for Research and Exploitation of Sea, he led the first recovery expedition to the Titanic in 1987.