Four people were on board the Irish Coastguard Rescue Helicopter 116 when it went down on 14 March.
Cpt Dara Fitzpatrick died after she was rescued from the sea.
Police said that the body of another crew member had been found but they could not yet confirm identification.
The missing coastguard crew were Cpt Mark Duffy, winch operator Paul Ormsby and winchman Ciaran Smith - it is not yet known which member has been found.
Search teams are trying to remove the body of the crew member from the cockpit of the aircraft, but investigators said sea conditions have meant dives to the wreckage on Saturday have been prevented.
On Friday the black box recorder from the rescue helicopter was recovered.
The chief inspector with the Irish Air Accident Investigation Unit (IAAIU) Jurgen Whyte said: "We're happy to announce we had a positive recovery of the data recorder at 1630 from the seabed just off Blackrock."
Mr Whyte said the recorder will be brought to Dublin before being sent to the UK air accident investigation branch where it will be prepared for download, hopefully successfully, by Tuesday or Wednesday of next week.
Late on Friday afternoon, searchers began diving at Blackrock island off the coast of Blacksod, County Mayo, where the wreckage of the helicopter was found on Wednesday
It was discovered about 60m west of Blackrock island, in waters about 40m deep.
R116 lost contact with the Irish Coastguard at about 01:00 on 14 March, as it made its final approach to Blacksod refuelling depot.
The crew had been providing communications support to another coastguard helicopter that had been deployed to take an injured fisherman to hospital.
The wreckage of R116 was pinpointed after search teams deployed a remotely-operated vehicle (ROV), fitted with an underwater camera.
The body of a crew member has been located in the wreckage of a rescue helicopter which crashed earlier this month, gardaÃ­ (Irish police) have confirmed.