The latest search operation is expected to last five days
Fresh efforts are getting underway this morning to locate the bodies of missing Rescue 116 crewmen Paul Ormsby and Ciaran Smith.
The Garda Water Unit is working with the specially adapted fishing vessel, 'MSV Westbound' near Blackrock Island off the north Mayo coast.
The Dublin-based coastguard helicopter crashed in March - after information systems onboard the aircraft reportedly failed to pick-up the lighthouse located on the Island.
There were four crew members on-board on the night.
The bodies of Captain Dara Fitzpatrick and Mark Duffy were recovered following the initial searches - but no trace has been found of the other crew members.
Garda diving teams are on standby to assist in the search and it is hoped sonar equipment and a special underwater camera attached to the fishing vessel will help in locating any human remains.
Garda Superintendent Tony Healy - who is coordinating the recovery operation - told Newstalk Breakfast that the latest search effort will last five days.
Photo Journalist Fergus Sweeney - who's based in Blacksod – said search teams will trawl the seafloor working off a pre-determined grid.
“Four months now has passed since the actual accident itself so I guess with the kind of weather conditions that have been in the area over the last couple of months, anything that might have been trapped below the surface may have come loose in that time," he said.
"It may have spread out so they just want to explore that avenue – the possibility that with the time period that has passed that some more clues from Rescue 116 might have been released.
This latest search effort was planned following the scaling back of the search in April.
The search was originally due to take place over the weekend, however bad weather hampered the operation.