Hopes of a rescue rise slightly - but numerous challenges remainpublished at 15:06 British Summer Time 21 June 2023

15:06 BST 21 June 2023

Pallab Ghosh
Science correspondent

The ocean is full of sounds, but reports suggest that the “banging” picked up by the rescue team is regular and so may be produced by a human source.

On board the missing craft is a retired French diver, who would know the protocol to alert search teams is to bang for three minutes every half an hour.

Rescuers will have been trying to pinpoint the location of the sounds using a series of buoys fitted with microphones in order to narrow down the search area. The next step is to lower a remotely operated vehicle (ROV) to locate the Titan using sonar and cameras.

If it is on the sea floor, the chances are that the vehicle has become entangled, possibly by wreckage from the Titanic. The ROV will have some capacity to move wreckage using robotic arms. But the possibility of success will depend on the extent of the entanglement and the Titan’s orientation.

It must be stressed that in previous undersea rescue attempts – such banging signals have been checked and found to be spurious, notably in 2017 when the Argentinian submarine, ARA San Juan. Later analysis of the audio determined it was actually from a natural source and not from the submarine.

So while hopes of a rescue have risen slightly – there are still numerous uncertainties and challenges – not least the lack of time in the Titan’s emergency oxygen supply which is due to run out in just over 24 hours.

Image source, Getty Images

US journalist Michael Guillen recounts his harrowing experience of being trapped in a similar vessel during a dive in the North Atlantic back in 2000.

"As we approached the stern area we were caught up in a very fast-moving underwater current. So we ended up getting stuck in the propeller," Dr Guillen, who was at the time science editor at America's ABC network, told BBC Radio 4.

"All of a sudden, there was just a crash," he recalled.

They were stuck there for a better part of an hour and Guillen already had said his goodbyes in his mind.

"I'll never forget this thought that came to my head: this is how it's going to end for you."

But then, after the efforts of the pilot, they sensed something had changed and they sensed that they were floating.

The journalist recollects that all this was happening in complete darkness, as the pilot turned off the spotlight.

Click here to read more about Guillen's experience in 2000.

A friend of the British businessman Hamish Harding - one of the five people on board the Titan - has told the BBC about the 58-year-old British adventurer's final words before he set off on his Titanic dive.

Jannicke Mikkelsen said she is "terrified" and "not sleeping" as rescue efforts continue.

What happens if sub reaches the surface?published at 14:12 British Summer Time 21 June 2023

14:12 BST 21 June 2023

Victoria Gill
Science correspondent

Hannah in Plymouth asks: If the vessel did reach the surface, is there any way for the people inside to get fresh oxygen in or are they still reliant on the supply provided?

Submarine search and rescue expert Frank Owen told BBC News on Wednesday morning that “banging sounds” that have been detected by floating sonobuoys in the search could suggest the Titan could be at the surface.

But even if that is the case, the hatch is bolted closed from the outside and the crew will be reliant on the air supply inside the vessel.

Any rescue operation at the surface though would be much simpler than a rescue at depth.

Aircraft flying above the wreck site have been dropping sonobuoys - devices used to detect sound - into the ocean. Some underwater noises have been detected, though the source is currently unknown.

A remotely operated underwater vehicle (ROV) - Victor 6000 - is also being used in the search.

If you're just joining us, here is a recap of what's been happening:

• Rear Admiral John Mauger - who is leading the coast guard mission - told CBS News that this is an incredibly complex search and they are working with the international community to find the submersible
• Earlier the US Coast Guard confirmed that an aircraft had picked up noise from the ocean - but Mauger said there were a lot of metal objects at the Titanic site that could have been causing the banging
• Three more vessels have arrived at the search site, external, with one of them having side scanning sonar capabilities
• It's thought that the people on board the Titan submersible have less than 24 hours of oxygen supplies left

Stay with us as we continue to bring you live updates, as well as our experts answering your questions.

What certification does the submersible have?published at 13:36 British Summer Time 21 June 2023

13:36 BST 21 June 2023

Patrick Hughes
Science reporter

"I understand that this sub is virtually ‘home-made’ and has no certification from any scientific technical regulatory body whatsoever,” Tim Stafell asks. “Is this true?"

Most major marine operators require that chartered vessels are “classed” by an independent group, such as the American Bureau of Shipping (ABS).

Titan, the submersible involved in this case, is not classed according to Oceangate themselves. In a blog post from 2019, external, the firm claim that it is the innovation behind their vessel which makes it difficult for an external body to certify.

The BBC’s US partner CBS sent one of its reporters on a voyage with the same company last year to see the wreck of the Titanic.

In his report, David Pogue reads from what appears to be a waiver which describes the submersible as an “experimental” vessel, "that has not been approved or certified by any regulatory body, and could result in physical injury, disability, emotional trauma or death".

Pogue questioned CEO Stockton Rush about the ‘jerry-rigged nature’ of some of the components. In response, Rush said that the company worked with Nasa and Boeing to ensure the safety of the pressure vessel.

How would rescuers be able to bring the sub up?published at 13:25 British Summer Time 21 June 2023

13:25 BST 21 June 2023

Victoria Gill
Science correspondent

Joe Blackwell asks: How will they bring it to the surface if it has lost power and is at the bottom of the Atlantic?

At the time of writing, it is still unclear where the sub is. But experts the BBC has spoken to say that, if there was not a catastrophic event that damaged the vessel - like a fracture to the hull or a fire, it is likely to be on the surface or on the seabed.

If it is at depth, it may be stuck. One concern is that underwater currents may have swept it into some of the wreckage of the Titanic. A French vessel, equipped with a deep sea robot that can be deployed to search the depths at which the Titanic sits - about 3,800m - is en route to the search site and should arrive later on Wednesday. It will join a technically challenging race against the clock.

Any robotic vehicle that is deployed might need to help dislodge the sub, enabling it to float to the surface. Or there might be a need to cut away whatever obstacle has it trapped.

But the search and rescue team will need to locate Titan before they can plan for that.

Does the Titan submersible have food and water on board?published at 13:21 British Summer Time 21 June 2023

13:21 BST 21 June 2023

Victoria Gill
Science correspondent

Kul Chima in Birmingham wants to know if there is food and water in the Titan submersible.

While OceanGate - the company that operates the sub - has not responded to our questions about conditions and provisions on Titan, we understand from the accounts of those who have been aboard previously that food and water is available.

There is also what is described as a “rudimentary toilet” on the sub.

Our experts answer your questionspublished at 13:16 British Summer Time 21 June 2023

13:16 BST 21 June 2023

Big questions remain in the search for the missing submersible. Over the next few hours we'll be bringing you the important answers with our science correspondents Victoria Gill and Pallab Ghosh, and science reporter Patrick Hughes.

You can get in touch by emailing haveyoursay@bbc.co.uk, external

Or:

• WhatsApp: +44 7756 165803

• Tweet: @BBC_HaveYourSay, external

In some cases a selection of your comments will be published, displaying your name and location as you provide it unless you state otherwise. Your contact details will never be published.

• Please read our terms & conditions and privacy policy

People around the world have been sharing their views on this search, with many sending their best wishes to those involved.

Meanwhile, some people have been comparing the rescue efforts to other disasters including last Wednesday's migrant shipwreck, in which hundreds of people died.

Here's a recap of what Mauger said during his short interview with CBS News, our partner in the US:

• The search is "incredibly complex" and partners from the international community are working to find the submersible
• An aircraft with sonar buoys detected noise in the water yesterday, but "we don't know the source of that noise"
• A lot of metal objects are at the Titanic site - which could be the source of the noise
• The noise is "a target, it's a focus for us to look at", with vessels deployed nearby
• Teams will keep searching "as long as there's an opportunity for survival", with more vessels working at the search site and aircraft flying above

Mauger ends by saying they will continue to work and bring every resource to bear on the search "as long as there's an opportunity for survival".

He says more vessels will be working in the search site, and they will continue to fly in the air above.

Mauger now says there a lot of metal objects at the site - and this is why it is so important to engage navy experts who understand the science behind noise.

But he says of the noise: "It's a target, it's a focus for us to look at."

Mauger confirms that an aircraft with sonar buoys detected noise in the water yesterday, but adds "we don't know the source of that noise".

As we earlier reported, he says he has shared the data with the US Navy.

Image source, CBS

Here's the first line from Mauger's CBS interview.

He says this continues to be a complex search, and his thoughts are with the crew and their families.

He adds that they’re working very hard as part of an international effort at the search site.

Image source, US Coast Guard

We're expecting to hear soon from Rear Admiral John Mauger of the US Coast Guard, who is leading the search for the Titan submersible.

He is due to speak to CBS News, the BBC's partner in the US, in the next few minutes.

In 2018, experts from the Marine Technology Society wrote to Stockton Rush, external, the chief executive of OceanGate, expressing "unanimous concern" about the Titan.

In the letter unearthed by The New York Times,, external its authors warned of potential "catastrophic" issues with its design.

They also said OceanGate was making "misleading" claims about its design exceeding industry safety standards.

"It is our unanimous view that this validation process by a third-party is a critical component in the safeguards that protect all submersible occupants," the letter read.

The NYT said OceanGate declined to comment on the letter.

The Marine Technology Society is a community of ocean engineers, technologists, policy-makers, and educators promoting awareness and application of marine technology.

Image source, Via the New York Times

In 2022, the BBC filmed inside the OceanGate Titan submersible.

It's believed Stockton Rush, the chief executive of OceanGate who features in this video, is one of five people on the vessel.

Watch the full episode from The Travel Show here.

The last major update we had from the US Coast Guard - which is leading the search - came around six hours ago.

It said:, external

• Canadian P-3 aircraft detected underwater noises in the search area
• ROV (remotely operated vehicle) operations were relocated in an attempt to explore the origin of the noises
• Those ROV searches have yielded negative results but continue
• The data from the P-3 aircraft has been shared with the US Navy for further analysis, which will be considered in future search plans