By Steve Gorman and Joseph Ax
(Reuters) -A multinational search team scanned the sea near the century-old wreck of the Titanic on Thursday, the fifth day since a tourist submersible went missing with five people aboard and with just hours to go before its air supply was expected to run out.
The minivan-sized submersible Titan, operated by U.S.-based OceanGate Expeditions, began its descent at 8 a.m. (1200 GMT) on Sunday, losing contact with its support ship near the end of what should have been a two-hour dive to the wreck.
The Titan set off with 96 hours of air, according to the company, so its oxygen tanks would likely be depleted some time on Thursday morning, although precisely when depends on factors such as whether the craft still has power and how calm those on board are, experts say, and assumes the craft is still intact.
Rescue teams and relatives and friends of the Titan's five occupants took hope when the U.S. Coast Guard said on Wednesday that Canadian search planes had recorded undersea noises using sonar buoys earlier that day and on Tuesday.
The Coast Guard said remote-controlled underwater search vehicles directed to where the noises were detected had not yielded results. Officials said the sounds might not have originated from the Titan.
"When you're in the middle of a search-and-rescue case, you always have hope," Coast Guard Captain Jamie Frederick said on Wednesday, adding analysis of the noises was inconclusive. "With respect to the noises specifically, we don't know what they are."
The French research ship Atalante, equipped with a robotic diving craft capable of reaching depths even below the Titanic wreck which lies about 12,500 feet (3,810 metres) below the surface of the North Atlantic, has been moving to the area.
The French robot, called Victor 6,000, has arms that can be remotely controlled to help free a trapped craft or hook it to a ship to haul it up. The U.S. Navy is sending a special salvage system designed to lift large undersea objects, such as small vessels.
DEEP-SEA EXCURSION
The wreck of the Titanic, which sank in 1912 on its maiden voyage after hitting an iceberg, killing more than 1,500 people, lies about 900 miles (1,450 kms) east of Cape Cod, Massachusetts, and 400 miles south of St. John's, Newfoundland.
The Titan was carrying its pilot and four others on a deep-sea excursion to the shipwreck, capping a tourist adventure for which OceanGate charges $250,000 per person.
The passengers included British billionaire and adventurer Hamish Harding, 58, and Pakistani-born business magnate Shahzada Dawood, 48, with his 19-year-old son Suleman, who are both British citizens.
French oceanographer and leading Titanic expert Paul-Henri Nargeolet, 77, and Stockton Rush, founder and chief executive of OceanGate, were also reported to be on board. Rush is married to a descendant of two of the Titanic victims.
Sean Leet, who heads a company that jointly owns the support ship, the Polar Prince, said on Wednesday that "all protocols were followed" but declined to give a detailed account of how communication ceased.
"There's still life support available on the submersible, and we'll continue to hold out hope until the very end," said Leet, chief executive of Miawpukek Horizon Maritime Services.
Even if the Titan were located, retrieving it would present huge logistical challenges.
If the submersible had managed to return to the surface, spotting it would be difficult in the open sea and it is bolted shut from the outside, so those inside cannot exit without help.
If Titan is on the ocean floor, a rescue would have to contend with the immense pressures and total darkness at that depth. Titanic expert Tim Maltin said it would be "almost impossible to effect a sub-to-sub rescue" on the seabed.
Questions about Titan's safety were raised in 2018 during a symposium of submersible industry experts and in a lawsuit filed by OceanGate's former head of marine operations, which was settled later that year.
(Reporting by Steve Gorman and Joseph Ax; Additional reporting by Tim McLaughlin, Rami Ayyub, Tyler Clifford, Louise Dalmasso, Daniel Trotta, Brad Brooks and Ariba Shahid; Editing by Raju Gopalakrishnan, Edmund Blair and Emelia Sithole-Matarise)