The search for missing Malaysia Airlines flight MH370 is set to revisit 30 locations previously ruled out as the jet's resting place, as hopes of ever finding the victims fade once again.

Despite having previously been considered 'unlikely to be significant to the search', the locations are all places where search and rescue vessels made 'sonar points of interest'.

The Boeing 777 vanished on March 8, 2014 while on a flight between Kuala Lumpur and Beijing. All 239 people on board are presumed dead and there has been no sign of the plane's fuselage - although officials confirmed that a piece of wreckage washed on Reunion Island was from the plane.

Vanished: Despite having previously been considered 'unlikely to be significant to the search', the locations are all places where search vessels made 'sonar points of interest'. Pictured is the missing Boeing 777 itself

Found: Officials have confirmed that this piece of wreckage found on Reunion Island in July is from MH370

Discovery: Somewhat embarrassingly for the search teams, even the wreckage that washed up on Reunion Island came as a total surprise, being thousands of miles from many of the original search sites

The latest update in the ongoing search for MH370 is likely to dishearten victims' relatives, especially after many were buoyed by the discovery of the Reunion Island wreckage.

Returning to sites that have previously been ruled out means that at the very least investigators are no closer to discovering the plane than they were several months ago.

The Australian Transport Safety Bureau does appear to be related to the discovery of the Reunion Island wreckage, however, with search teams eager to revisit areas from where a large piece of wreckage could easily float to the island.

'The search for MH370 is being conducted thoroughly and to a very high standard and it is important that contacts are comprehensively investigated and considered,' the bureau told News.com.au.

They went on to say that on revisiting the 30 underwater sites, investigators will use 'higher frequency sonar' than in previous searches, giving them a greater chance of finding the jet.

The system is not without its frustrations, however, as if any sites stand out as being a particularly likely location for MH370, the search teams will have to wait until the weather improves next summer before an autonomous underwater vehicle can carry out a physical search.

Search: On revisiting the 30 underwater sites, investigators will use 'higher frequency sonar' than in previous searches, giving them a greater chance of finding the jet

Scanning the water: A Royal Australian Airforce plane carries out a search mission for possible MH370 debris

Tribute: A Malaysia Airlines employee writes a message expressing well-wishes for passengers of the missing Malaysia Airlines flight MH370 after it went missing in March 2014

There has been a great deal of criticism over how investigators have conducted the search for MH370 - including experts saying the wrong type of equipment is being used.

Somewhat embarrassingly for the search teams, even the wreckage that washed up on Reunion Island came as a total surprise, being thousands of miles from many of the original search sites.

The search for MH370 is being conducted thoroughly to a very high standard and it is important that contacts are comprehensively investigated and considered. - Australian Transport Safety Bureau

But with the plane having vanished over 18 months ago, the debris could by now have easily spread to locations far from the actual crash site, meaning the investigators are still no closer to finding the crucial fuselage, where the bodies of those on board are expected to be found.

Earlier this month an Air France captain spotted floating debris near Reunion Island where a piece of the doomed Malaysian Airways MH370 jet washed up in July.

The captain was flying at 10,000 feet and was on approach for the Island's Saint-Denis Roland Garros airport when he alerted authorities to the discovery.