Further attempts will be made on Monday if weather permits to try and pinpoint the black box from Rescue 116, the Irish Coast Guard helicopter which crashed off North Mayo on Tuesday.
Air, sea and shore searches are continuing along the Mayo coast for missing air crew Capt Mark Duffy, winch operator Paul Ormbsy and winchman Ciaran Smith.
Taoiseach Enda Kenny is expected to meet relatives of the airmen on a visit to Blacksod on Monday.
Mr Kenny, who attended the funeral of the helicopter’s pilot, Capt Dara Fitzpatrick, on Saturday, kept in close contact with the search effort during his visit to meet US president Donald Trump last week.
A short weather window on Sunday allowed deployment of two vessels equipped with multi-beam sonar to Blackrock lighthouse – 13 km offshore and the last known location of the helicopter on its approach to a refuelling point at Blacksod early on Tuesday morning.
The 12m Gearoidín and 7m Geological Survey of Ireland storm force rigid inflatable boats carried underwater imaging equipment to try and locate the black box flight recorder, which emitted a faint signal in 40m of water 50 to 60m from the lighthouse plateau on Wednesday.
Marine Institute surveyors and Naval Service divers on board the two vessels were accompanied by a fisherman familiar with the waters known for their strong tides and currents.
The vessels were provided with shelter by the Naval Service patrol ship LÉ Eithne.
The Irish Lights ship Granuaile, carrying the largest in a series of remotely operated vehicles (ROVs) deployed for the search, also arrived in Blacksod Bay over the weekend.
Equipment
The 80m ship has a dynamic positioning system that allows it to remain on location in a heavy swell, and is equipped with lifting gear and a diving platform.
The Marine Institute's largest ROV, named Holland 1, which was loaded onto the ship in Galway on Saturday, is equipped with two robotic arms, high definition cameras and sonars, and can work at 3,000m in depth.
Marine Institute research vessel manager Aodhán Fitzgerald said the challenge in this location is not the depth of the black box signal, which is only 40m, but the sea surge in and around the area.
The ROV can be deployed laterally from the Granuaile and, if successful, is far safer than using diving teams. Naval Service divers are on standby, however, and the depth is within their limits.
The RNLI Achill and Ballyglass lifeboats, which have been undertaking sweeps of Achill island, Blacksod Bay and the Mullet peninsula since early on Tuesday, were out at sea again on Sunday with voluntary crews.
The shore searches are being co-ordinated by the Irish Coast Guard Ballyglass unit. Irish Coast Guard spokesman Declan Geoghegan said that areas where wreckage and debris had been found were being revisited.
The Irish Coast Guard Sligo helicopter, which has been rotating air searches with its Shannon counterpart, was diverted when some divers got into difficulty after their dive boat capsized off the Co Sligo coast and eight people were rescued.
