Mike Wendling
BBC News

Image source, David Lochridge

A submarine expert who worked for OceanGate – the company that operates the missing submersible – warned of potential safety problems in 2018, according to US court documents.

David Lochridge moved from Scotland to Washington state to work for the firm. In a BBC interview in 2017 he enthused about the mission and said it was "destined for the sea".

But less than a year later he warned his bosses that flaws in the Titan's carbon hull might go undetected without more stringent testing, and urged the company to have an outside agency certify the vessel.

He said his verbal warnings were ignored until he wrote a report and was called into a meeting with several officials - including OceanGate chief executive Stockton Rush, who is aboard the missing submersible.

OceanGate responded by firing Lochridge. The company sued him for revealing confidential information, and the submarine expert countersued for unfair dismissal. The lawsuit was later settled.

Through his lawyer, Lochridge declined to comment.

Court documents also state that Lochridge learned that the manufacturers of the Titan’s forward viewport only certified it to a depth of 1,300 metres. The Titanic wreck lies 3,800 metres below the ocean surface.

Shortly after midnight local time in Newfoundland, Canada, the first reports emerged of potential signs of hope.

Two US media outlets reported a leaked internal memo sent to the US Deparment of Homeland Security.

This said a Canadian aircraft had detected underwater "banging sounds" in 30-minute intervals coming from the search area.

"The P8 [seacraft] heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed and banging was still heard," Rolling Stone magazine reported the email as saying.

CNN also reported an internal update sent Tuesday night, which suggested more sounds were picked up.

“Additional acoustic feedback was heard and will assist in vectoring surface assets and also indicating continued hope of survivors,” said the second memo according to CNN's report.

An hour after the media reports, the US Coast Guard confirmed that a Canadian search aircraft had picked up "underwater noises".

The Titan submersible could be in ultra deepwater - the craft is capable of reaching 4,000m in depth.

It was on its way to the site of the Titanic wreck, which lies on the ocean seabed at a depth of 3,800m.

The sub lost contact about one hour and 45 minutes into its two hour dive to the wreck.

There has been no sign of it so far. However, authorities in the past few hours have confirmed that they have detected "underwater noises" in a sonar search of the area.

The US Coast Guard said it had relocated operations to zero in on the sounds' origins but nothing has been found so far.

The crew of the Titan submersible lost contact with its support surface vessel, the Polar Prince, an hour and 45 minutes after it began a dive to see the wreck on Sunday.

Titanic's wreck lies 435 miles (700km) south of St John’s, Newfoundland, in Canada, though the rescue mission is being run from Boston in the US.

The US Coast Guard said about an hour ago a Canadian search aircraft had detected "underwater noises" in the search area.

Remotely operated vehicles were relocated "in an attempt to explore the origin of the noises" but have so far "yielded negative results".

The US Coast Guard's Northeast Command said on Twitter, external these relocated searches continue.

The discovery of noises were first reported by US media, about an hour before official confirmation.

CNN and Rolling Stone reported that an internal US Department of Homeland Security memo said a Canadian aircraft had picked up "banging noises" heard in 30-minute intervals on Tuesday.

"Banging was still heard" four hours after the inital pick-up, when additional sonar was deployed to the area, the memos said according to reports.

Image source, OceanGate

• The missing sub, dubbed the Titan, has less than 30 hours of emergency oxygen left, based on previous estimates
• The US Coast Guard just said that a Canadian search aircraft picked up "underwater noises", external in the search area, but it is unclear when and how long the noises lasted
• Among the five passengers onboard are British billionaire Hamish Harding, British-Pakistani businessman Shahzada Dawood and French explorer Paul-Henry Nargeolet
• On Sunday, the sub lost contact with its support ship one hour and 45 minutes into its two-hour dive down to the Titanic wreck site, which lies at a depth of 3,800m
• Search and rescue operations have covered an area of 7,600 sq miles (19,650 sq km), larger than the US state of Connecticut

Image source, SUPPLIED

If you're just catching up on this story, here's a quick reminder of who the five passengers onboard are:

• Hamish Harding, 58, a British adventurer who has previously been to space and - multiple times - to the South Pole
• British businessman Shahzada Dawood, 48, a member of one of Pakistan's richest families and a supporter of two charities founded by King Charles
• His son Suleman Dawood, a 19-year-old student
• Paul-Henry Nargeolet, 77, a former French Navy diver who has reportedly spent more time at the Titanic wreck than any other explorer and was part of the first expedition to visit it in 1987
• Stockton Rush, 61, the chief executive of OceanGate, the firm that operates the Titanic voyages

Here is what we know about them.

We're continuing our live coverage of the ongoing search for the tourist submersible that went missing on Sunday while taking five people to view the wreck of the Titanic.

We’ve just heard that an underwater sonar search on Tuesday picked up "banging" noises from an the area where the sub disappeared off the coast of Newfoundland in Canada. Rescuers are racing against the clock as the vessel’s supply of emergency oxygen is expected to run out by Thursday.

Follow as we bring you the latest updates.