Rescue teams were racing on Wednesday (Jun 21) to trace the origin of sounds heard from the depths of the North Atlantic in a search for a tourist submersible with five people on board that vanished on its descent to the century-old wreck of the Titanic.

The US Coast Guard said remotely operated vehicle (ROV) searches were deployed in the area where Canadian aircraft detected the undersea noises on Tuesday, as the clock ticked in the last 24 hours of the missing craft’s presumed air supply.

“Those ROV searches have yielded negative results but continue,” the US Coast Guard wrote on Twitter on Wednesday.

The 6.4-metre submersible Titan, operated by US-based OceanGate Expeditions, began its descent at 8 am (1200 GMT) on Sunday, according to the US Coast Guard. It lost contact with its parent surface vessel soon after that during what should have been a two-hour dive to the Titanic.

The mini-sub was designed to remain underwater for 96 hours, according to its specifications. That would give its occupants enough air until roughly 1200 GMT on Thursday, if it remained intact. Experts said a range of factors affected that deadline including whether it still had power in the icy depths.

The wreck of the British ocean liner, which sank when it hit an iceberg on its maiden voyage in 1912, lies on the seabed at a depth of about 3,810 metres. It is about 1,450 km east of Cape Cod, Massachusetts, and 643 km south of St John’s, Newfoundland.

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Those aboard the submersible, the highlight of a tourist expedition that costs US$250,000 per person, included British billionaire and adventurer Hamish Harding, 58, and Pakistani-born businessman Shahzada Dawood, 48, with his 19-year-old son Suleman, who are both British citizens.

French explorer Paul-Henri Nargeolet, 77, and Stockton Rush, founder and chief executive of OceanGate Expeditions, were also reported to be on board. The authorities have not confirmed the identity of any passenger.

A friend of Harding, Jannicke Mikkelsen, who has accompanied the British entrepreneur on other expeditions, told Reuters on Tuesday she was hoping for good news but was not optimistic. “It would be a miracle if they are recovered alive,” she said.

Teams from the United States, Canada and France have been involved in the search, covering an area of open sea larger than the US state of Connecticut or about half the size of Belgium.

Aircraft and ships from the US Coast Guard, US Navy and Canadian armed forces had combed more than 19,700 square km of the North Atlantic, US Coast Guard Captain Jamie Frederick said on Tuesday.

The Canadian military dropped sonar buoys to listen for any sounds that might come from the Titan and a commercial pipeline-laying vessel with a remote-controlled deepwater submersible was also searching, he said. A French research ship carrying a deep-sea diving robot submersible was dispatched to the area at the request of the US Navy and were expected to arrive later on Wednesday, France’s Ifremer ocean science research institute said.

US Coast Guard said Canadian Lockheed P-3 Orion aircraft, which have sub-surface surveillance gear to trace submarines, detected the underwater noises in the search area on Tuesday.

Remote undersea equipment was deployed in the area where the sounds were detected and data from the P-3 aircraft was shared with the US Navy experts “for further analysis which will be considered in future search plans,” the US Coast Guard wrote in its Twitter statement.

It did not give details about the nature of the sounds, but CNN and Rolling Stone magazine, citing internal US government communications, reported Canadian aircraft detected banging sounds at 30-minute intervals in the area.

Rolling Stone said the sounds were picked up by sonar buoys and that sonar picked up more banging four hours later.

CNN, citing a US government memo, said additional sounds were heard about four hours after the banging was detected but said the second occurrence was not described as banging.

Experts say rescuers face major obstacles both in finding the Titan and in saving the people aboard.

In the event of a mid-dive emergency, Titan’s pilot would likely have released weights to float back to the surface, said Alistair Greig, a marine engineering professor at University College London. But he said it would be difficult to locate the van-sized submersible in the Atlantic without any communication.

The submersible is sealed with bolts outside, preventing occupants escaping without assistance even if it surfaced.

If Titan were stuck on the ocean floor, a rescue effort would face even bigger challenges because of the huge pressures and total darkness at a depth of more than 2 miles. Titanic expert Tim Matlin said it would be “almost impossible to effect a sub-to-sub rescue” on the seabed.

The sinking of the Titanic, which killed more than 1,500 people, has long been immortalized in books and films. Popular interest was renewed by the 1997 blockbuster movie “Titanic”. REUTERS