The exploratory dives come after it emerged that the R116 may have struck rocks on the western side of Blackrock island.
Yesterday evening, a spokesman for the Department of Transport, Tourism, and Sport said rescue workers were hopeful of a “window of opportunity” to carry out the first dive of the area this morning.
Bad weather, including strong swells and high winds, have severely hampered the retrieval of R116’s black box, which was detected at 4pm last Wednesday.
The Irish Lights vessel the Granuaile was being prepared yesterday in the event of a dive and retrieval of the helicopter today.
A remotely operated vehicle, a recompression chamber, and other specialist diving equipment were transferred on to the Granuaile yesterday, which has a platform and can lift up to 20 tonnes of weight.
The first dive could take place as early as 6am today.
The Irish Coast Guard’s Declan Geoghegan said the search team is hopeful that swells will have gone down by this morning.
It is hoped that the improved weather continues and that more diving can be carried out into Thursday.
The R116 rescue helicopter crashed in Blacksod Bay, off the Mayo coast, in the early hours of Tuesday, March 14, claiming the life of its captain Dara Fitzpatrick.
Its three other crew members, Mark Duffy, Ciarán Smith, and Paul Ormsby, are still missing.
Capt Fitzpatrick’s funeral took place last Saturday.
While the helicopter’s black box was detected just 36 hours after the crash, weather restricted the search team with a mapping out of the sea only being carried out last Sunday.
The Air Accident Investigation Unit (AAIU) inspected R116 wreckage found on the island where Blackrock lighthouse stands.
On Tuesday evening it released a statement on its findings: “There appear to be marks on some of the recovered wreckage which are consistent with the tail of the aircraft contacting rocky surfaces on the western end of Blackrock.”
“The investigation has not yet definitively identified the initial point of impact,” it stated.
The AAIU also said that a “significant amount of wreckage has been recovered from the sea”, despite the main bulk of the craft yet to be recovered.
Taoiseach Enda Kenny, who has visited the area, said that the families of the missing crew members need answers.
Mr Kenny said: “What we need to find out here is what happened. There are four families involved in this and they need to know, obviously, to bring closure to this but also in respect of the service itself and the facilities that are provided.”