The crew of a Royal Navy ship are "working 24/7" to hunt for flight recorders from the missing Malaysian plane, their commander has said.
HMS Echo is helping to scour the southern Indian Ocean after Malaysia Airlines flight MH370 vanished with 239 people on board on 8 March.
Sonar "pings" were detected last week by search teams - but no new signals have been confirmed since last Tuesday.
Cdr Phillip Newell said the search was proving to be "challenging".
Plymouth-based hydrographic survey ship HMS Echo was diverted from gathering data on its way from Oman to the Seychelles to help in the search.
The ship, whose specialist equipment has been adapted to pick up signals from the plane's black box flight recorders, arrived in the search area on Thursday.
"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," said Cdr Newell.
"There's a sense that we are playing an important part in this role and we are keen to get it right."
Australian defence vessel Ocean Shield has been using a US Navy towed pinger locator to listen out for signals, which were detected twice last weekend and twice on Tuesday.
Australian Prime Minister Tony Abbott said he was confident the signals were from the black box - but on Saturday he warned those signals were "rapidly fading".
Prime Minister Abbott said finding the jet would be a "massive, massive task"Cdr Newell - who has 20 years experience searching sea beds - said bad weather was also causing difficulties in interpreting the signals.
"It should never be underestimated that trying to find an object this small on the sea bed at this depth is probably as hard a challenge as you will ever get," he said.
Cdr Newell said it was "humbling" to be able to provide support to the international search effort 
HMS Echo's specialist equipment has been adapted to pick up sonar pings 
The UK is also aiding the search with nuclear submarine HMS Tireless He said another challenge was directing Australian P-3 Orion aircraft which are dropping sound-locating buoys into the water.
Continue reading the main story 8 March: Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappearsPlane's transponder, which communicates with ground radar, was switched off as it left Malaysian airspaceSatellite 'pings' indicate plane was still flying seven hours after satellite contact was lost24 March: Based on new calculations, Malaysian PM says "beyond reasonable doubt" that plane crashed in southern Indian Ocean with no survivors"It's key to make sure that we detect anything that can help in the investigation," said Cdr Newell, adding that the UK had "the right capability, in the right place at the right time".Search teams are trying to pinpoint the source of the signals so they can send down a robotic submersible to look for wreckage and black boxes.
The UK's contribution to the search also includes nuclear submarine HMS Tireless, which has advanced underwater search capabilities.
Australia is overseeing the day-to-day operations via its newly created Joint Agency Coordination Centre. Eight countries are involved in the search.
As well as naval ships from the UK and Australia, investigators are using military aircraft from a host of countries and an ice-breaking research ship from China.
'Time running out'Malaysia Airlines Flight 370 was flying from Kuala Lumpur to Beijing when it lost contact with air traffic controllers last month.
Officials believe the plane flew off course for an unknown reason and went down off the west coast of Australia.
But those involved in the search believe time could be running out because the battery life of a black box usually lasts for only a month - and that window has passed.
Before arriving in the latest search area, HMS Echo had already searched 6,000 square miles (15,540 square km) of ocean 1,000 miles (1,609km) north-west of Perth.
Cdr Newell said the ship would continue to provide support until its tasking was reviewed later this month.