The hunt for the black box from missing Malaysia Airlines flight MH370 is proving "challenging", but the crew of a Royal Navy ship are working 24/7 in their efforts to help the search, their captain has said.
Survey ship HMS Echo is in the southern Indian Ocean helping in the underwater search for the flight recorder from the missing jet.
Flight MH370 disappeared on March 8 with 239 people on board, sparking an international effort to find out what happened to it.
Hydrographic survey ship HMS Echo was diverted from work in the Indian Ocean to help in the hunt, and arrived on Thursday in the area of the southern Indian Ocean where "pings" thought to be from the missing plane had been detected.
Australian prime minister Tony Abbott said on Friday that crews had significantly narrowed down the search area in the hunt for signals which authorities are confident are from the missing jet.
But he said the signal from the Boeing 777's flight data and cockpit voice recorders is fading - batteries powering their locator beacons last only about a month and it has been more than a month since the plane disappeared.
Ocean Shield, which is towing a US Navy device to detect signals from the beacons, first picked up two underwater sounds consistent with the "pings" last Saturday, followed by two more in the same general area on Tuesday.
Searchers are trying to pinpoint the location of the source of the signals so they can send down a robotic submersible to look for wreckage and the flight recorders.
HMS Echo, whose specialist equipment has been specially adapted to pick up sonar pings from the jet's missing black box, is supporting Ocean Shield by understanding the signals it is picking up, its commanding officer said.
Speaking from the ship today, Commander Phillip Newell said they are working in conditions after inclement weather caused difficulties interpreting signals picked up underwater.
He said: "It's been challenging. Over the last couple of days we have been conducting oceanographic observations to support Ocean Shield.
"The key thing is to help their understanding of what is going on, and how it is affecting the ocean column."
He said there had been some difficult weather conditions which had "messed up" the water column, making it hard to understand some signals being picked up.
"The key challenge is to try and refine all of the observations they are making. They are doing that at the moment but it's challenging.
"Looking out of the window right now, what we are seeing is Ocean Shield to the south of us conducting further observations.
"She is trying to get in a position so she can then observe on the seabed, and then through the water column, the pings from the black box, which involves physically moving the ship."
He said another challenge is directing Australian navy P-3 Orion aircraft which drop sound-locating buoys, each dangling a hydrophone listening device about 1,000 feet below the surface, into the water.
Cdr Newell said he and his crew are conscious of the importance of their task and need to refine the search area while the black box's signal can still be detected.
"At this stage it's a challenge trying to refine this position so that when they put a submersible into the water they will be in a position where they can identify what is on the seabed correctly.
"We have got to give them the best advantage we can and within that they will get to the position where they have the best refined position that they can search."
He added: "In anything like this I am very conscious, I have 20 years experience of trying to find things on the seabed, it's pretty much my day job.
"I have a brilliant team, young, bright and enthusiastic and we are working 24/7 to cover the sea bed and observe on the surface.
"There's a sense that we are playing an important part in this role and we are keen to get it right.
"In terms of purpose, it's key to make sure that we detect anything that can help in the investigation."
Before arriving in the latest search area HMS Echo had already searched 6,000 square miles of ocean - an area 10 times the size of Greater London - 1,000 miles north-west of Perth with Chinese vessels after sensors picked up a possible signal on April 5.
The Plymouth-based ship was gathering data on her way from Oman to the Seychelles when she was diverted to join the international search for the Malaysia Airlines plane.
Apart from a 12-hour stop in the Maldives to take on supplies and change some of her crew, the survey ship has now been at sea continuously for six weeks.
Cdr Newell said: "We are a ship that's designed and built to operate for long periods at sea. We can carry provisions for 60 days at sea, and fuel to go pretty much halfway round the world", and said the ship would carry on helping with the search, providing as much support as it could to Ocean Shield until its tasking is reviewed later in the month.
The search is also being helped by nuclear submarine HMS Tireless.