In the past few hours two ROVs, remote operated vehicles, have descended to help in the search for the Titan.

However, efforts to fly out another ROV - called Juliet - belonging to the Guernsey-based deep-sea survey firm Magellan have hit a snag.

It was initially loaded late this morning onto a US military aircraft at Jersey Airport but they struggled to fully get it on, according to Magellan's chief executive Richard Parkinson. That means they now have to take if off and wait for another aircraft to arrive.

Here is what things looked like in Jersey as they prepared to transport the submersible.

Image source, Flightradar

Flight tracking shows a Royal Air Force C-17 transport aircraft has now left Lossiemouth in the north of Scotland carrying equipment to help with the search for the missing Titan submersible (see our post here)

The aircraft is understood to be carrying cabling to St John's in Newfoundland, Canada, the airport nearest to the site of the Titanic wreck.

Victoria Gill
Science correspondent, BBC News

The chances of finding something on the sea floor at depth - using a remotely operated vehicle (ROV) - depend on how tightly the search area can be defined, marine geophysicist Dr Rob Larter has said.

“We've all seen the reports of the sounds that have been detected,” he told press briefing earlier this morning.

“But the fact that the search area is still so large would seem to indicate that nobody [has] confidently been able to locate where those sounds are coming from.”

Each of the floating sonobuoys should be able to give a bearing, so depending on the number and location of buoys in relation to the location of the sound source, that could provide what submarine search and rescue expert Frank Owen described as “a cross-fix” on the sound.

“That should be possible,” he told me. “But [if it’s Titan] they’re banging on a carbon fibre hull, not a steel hull.

“That’s like banging a log, instead of banging a bell - it’s less loud and more muffled, so it’s not a crisp, clear noise. That may not propagate through the water anywhere near as well.”

Image source, EPA-EFE/REX/Shutterstock

Downing Street has confirmed that a Royal Navy submariner as well as equipment from a UK firm will help the search operation for the Titanic sub.

A No 10 spokesperson has said Lieutenant Commander Richard Kantharia has "significant knowledge of submarine warfare and dived operations".

Meanwhile, a Royal Air Force C-17 transport aircraft is currently being loaded up at RAF Lossiemouth and will depart for Canada this afternoon with ancillary equipment - believed to be cabling - on board.

No 10 has said the decision follows a request from the US Coastguard.

Rebecca Morelle
Science editor

Magellan’s ROV - Juliet - is currently at Jersey Airport in the Channel Islands, and will soon be on its way to the search site taken by a US military transport aircraft.

This will take time though.

Magellan estimates it will take about 50 to 60 hours to get all of their gear there, which would take us into the weekend.

The sub has been ready for dispatch since Monday - awaiting transportation from the US authorities. And there has been frustration about the delays.

Yesterday the Explorer’s Club - a professional society dedicated to research and exploration - tweeted that it had been working on approval for Magellan’s ROVs to be allowed to be deployed to the site as they believed they could offer valuable assistance.

Its president Richard Garriott tweeted that the ROV should have been accepted sooner., external

Time has never been more of the essence with a rescue effort like this.

Rear Admiral John Mauger, of the US Coast Guard, has said the operation to find the missing submersible is "still an active search and rescue".

Asked if he believes the oxygen on board will have run out by now, Mauger told Sky News: "We continue to keep the crew members and the families in our thoughts as we proceed with this search and rescue while we're cognisant of the time and we've factored in a lot of data and information into the search.

"This is still an active search and rescue at this point and we're using the equipment that we have on the bottom right now, the remote operated vehicles to expand our search capability, and then also to provide rescue capability as well."

Lorna Gordon
Reporting from Ifremer's Underwater Systems site in France

Many of those who work at the French oceanic research institute, Ifremer, which is helping in the search for the Titan, know Paul-Henri Nargeolet.

The missing French explorer worked here at the institute, based in the south of France, before he started a second career dedicated to the Titanic.

Xavier Placaud who has made 20 trips to the Titanic, and who can pilot the remotely operated vehicle the Victor 6000 which is being used in the search, has remained at base.

He said Paul-Henri used to be their director on one of submarines the institute operates and that: “I dived with him on the Titanic once or twice so we know him well.”

Paul-Henri is, he said, “A character, an adventurer, he's the Titanic encyclopaedia for us, he's a great man because he's done a lot of submarine diving. He is passionate, an adventurer who has shared his passion with us.”

He added, “ We all hope we'll find him quickly. We're sure we'll find them, that’s what we are hoping.”

Image source, AFP

Victoria Gill
Science correspondent, BBC News

Image source, Reuters

If the banging sounds that have been picked up by floating detectors called sonobuoys are coming from the missing Titan submersible, experts say they will be difficult to pinpoint.

Marine geophysicist Dr Rob Larter explained that the chances of finding something on the sea floor at depth - using a remotely operated vehicle (ROV) - depended on how tightly the search area could be defined.

“We've all seen the reports of the sounds that have been detected,” Dr Larter said in a press briefing on Thursday morning.

“But the fact that the search area is still so large would seem to indicate that nobody [has] confidently been able to locate where those sounds are coming from.”

Each of the floating sonobuoys should be able to give a bearing, so depending on the number and location of buoys in relation to the location of the sound source, that could provide what submarine search and rescue expert Frank Owen described as “a cross-fix” on the sound.

“That should be possible,” he told me. “But [if it’s Titan] they’re banging on a carbon fibre hull, not a steel hull.

“That’s like banging a log, instead of banging a bell - it’s less loud and more muffled, so it’s not a crisp, clear noise. That may not propagate through the water anywhere near as well.”

In the last half-hour it has been confirmed that two deepwater ROVs, or remotely operated vehicles, have arrived at the site with one having reached the sea floor.

The United States Coast Guard said on social media the submersible , externalattached to the Canadian vessel Horizon Arctic had reached the sea floor.

The Victor 6000, which is operated from the French research vessel Atalante, has also been deployed.

The search for Titan is proving difficult.

The submersible could be in ultra-deep water as it is capable of reaching a depth of 4,000m - enough to reach the Titanic wreck which lies at 3,800m beneath the surface.

Radio and GPS signals can't travel through water, therefore remotely operated vehicles (ROV) are being used for the search instead.

The French submersible Victor 6000, which is being used at this stage, is capable of reaching the sea bed and transmitting images to the surface as well as carrying out extremely delicate manoeuvres such as cutting or removing debris.

Image source, Reute

A teenager trapped on the submersible Titan is a student in Glasgow, BBC Scotland has learned.

Suleman Dawood, 19, studies at the University of Strathclyde.

He is one of five people on board the sub, including his father Shahzada, 48, a businessman who lives in Surbiton, south-west London.

Read more.

Rebecca Morelle
Science editor

Image source, Magellan

Here are some more details on the remotely operated vehicle (ROV) I mentioned in my last post, which is currently at Jersey Airport and due to be flown to the search site later today.

The ROV - called Juliet - scanned the Titanic wreck last summer. It spent 200 hours surveying the site, producing remarkable 3D scans of the wreck and its debris field.

It’s an Argus Worker XL and is able to dive to 6,000m - well beyond the depth required in the search area.

It’s an extremely capable ROV, and very experienced at operating at extreme depths. You can view the technical specs here, external. It will aid the search using sonar.

The company now estimates it will take about 50 to 60 hours to get to the site.

Emma Owen
Live reporter

Image source, Reuters

It's lunchtime in London, and early morning in St John's Harbour in Canada. The sun rose a few hours ago on the fourth full day of the search for the Titan submersible.

Here's the latest:

• Additional deep-sea search equipment has arrived in the area, and more is on its way
• A French vessel with a submersible capable of reaching the sea bed and transmitting images to the surface is in position
• Another submersible that has previously scanned the wreck of the Titanic will shortly be flown in from Jersey
• According to previous estimates, oxygen supplies for those on board will be very low by now

We're expecting to hear more from the authorities later today - we'll keep you posted when we know more.

As the search for the submersible continues, here's a brief recap of the time frames involved:

• Titan was launched from the Polar Prince at 08:00 local time on Sunday morning
• Contact was lost one hour and 45 minutes into its descent, at about 09:45
• The Coast Guard said they were notified of the problem at about 17:45 - eight hours later
• Search efforts began soon after

• Titan usually dives with a four-day emergency supply of oxygen
• On Monday the US Coast Guard told a news conference it anticipated there was "somewhere between 70 and the full 96 hours available" at that point

Lorna Gordon
Reporting from Ifremer's Underwater Systems site in France

The Victor 6000, a submersible operated by the French research institute Ifremer, has arrived in the search area.

Working in four-hour shifts, a team of two pilots will navigate and control its movement from a control room on board the surface ship, the Atalante.

There will also be a third person in the control room helping with the mission. They could be from the Canadian coastguard or from the company which operates the missing submarine the Titan.

The lights and cameras that Victor 6000 has on board will enable the team on the surface ship to see in real time what is on the floor of the ocean to a distance roughly equivalent to a small tennis court.

The French submersible also has two mechanical arms capable of extremely delicate manoeuvres such as cutting or removing debris.

The atmosphere back at their base in the South of France is calm. They know the team operating the Victor 6000 out in the Atlantic is extremely experienced.

Image source, .

Pallab Ghosh
Science correspondent, BBC News

I've been speaking to a group of UK submersible experts this morning about the chances of a successful rescue.

Dr Rob Larter of the British Antarctic Survey said “although it’s a desperate situation, there’s hope, and you have to stay optimistic for as long as possible”.

He explained that it was impossible for the ships on the sea surface to find the Titan using sonar, because it was so small.

And the only undersea remotely operated vehicle (ROV) capable of working at the required depth, the Victor 6000 had arrived on the scene just last night.

He noted the banging sounds first heard on Wednesday had not led to the search area being narrowed.

Prof Alistair Greig from University College London said that if the Titan was found trapped in wreckage on the sea bed it would normally take two hours for it to rise to the surface under its natural buoyancy once it had been released by an ROV.

“Every step takes time and time is what we are running out of,” he said.

Image source, US Coastguard

Earlier we posted this image from the US Coast Guard showing search patterns for the Titan, and promised to make sense of it for you.

So we've asked Dr Jamie Pringle, from Keele University about it.

“There is no scale on it, which is not super helpful,” he says.

“You will see there is a variety of different grids on there, some of them are denser than others. It is 2D as well, and remember we are in a 3D environment - we are not sure if this is from the surface or further down in the water.

“I think that X shows you where the Titanic is, and it is interesting that the grids aren’t centred so the Titanic’s not in the middle.”

He adds the fact the search area is so large "suggests that the rescue team has not narrowed down the area as a result of the banging sounds".

"The fact that some of the grids are longer than others and different shapes suggests that different instruments are being used.”

Does that help? A bit, we hope.

The search operation is made up of US and Canadian agencies, navies and commercial deep-sea firms are all helping the rescue operation, which is being run from Boston, Massachusetts.

They all have different capabilities, and here's what we know about each one:

Deep Energy - Commercial cable-laying ship with two ROVs that can operate down to 3,000m (10,000ft)

Atlantic Merlin - Canadian offshore supply vessel with 4,000m winch system. Carries ROVs but it's unknown how deep they can operate

Skandi Vinland - Subsea support vessel with two ROVs but it's unknown how deep they can operate

L'Atalante - French-operated ship heading to the scene with an ROV that can operate at depth of Titanic wreckage

Horizon Arctic - Commercial vessel loaded with support equipment

Glace Bay - Canadian naval ship carrying decompression chamber and ready to provide medical assistance

John Cabot - Scientific research vessel with sonar search capabilities operated by the Canadian Coast Guard

Jessica Parker
Reporting from Boston

Officials here say they are still in full search and rescue mode.

Fresh equipment is, as I write, being channelled towards the remote part of the North Atlantic that’s now the focus of an international operation.

I’ve been in Boston since Monday, from where this is all being coordinated. It was clear early on that help might be needed from military specialists as well as commercial firms – and so it’s proved to be.

Cutting edge under-sea robotics and heavy duty winching equipment are among the resources they’re now trying to deploy.

And while the operation has grown, so has the press attention.

The coastguard’s news conferences here have intensified both in their tone and attendance as the world watches for developments in what is now a five day long search for the missing sub.