LATEST: A ping from the black box flight recorder from Rescue 116 has been located.
A massive air, sea and shoreline search has been ongoing off the Mayo coast since the helicopter disappeared from radar screens in the early hours of Tuesday morning.
Captain Dara Fitzpatrick was confirmed dead yesterday, but Mark Duffy, Paul Ormsby and Ciaran Smith are still missing.
Members of the Air Corps, coastguard, navy and Gardai are all involved in the search operation.
Jurgen Whyte is the Chief Aeronautical Officer with the Air Accident Investigation Unit.
He says locating a ping from Black Box is significant:
"It's hugely significant. Other investigation authorities have spent months trying to do the same thing. We've been very lucky that within less than 36 hours we've picked up what is a signal. What that means is the recorder has activated its beacon and we're now using sophisticated equipment to hone in on the signal itself."
Captain Dara Fitzpatrick was 1 of 4 on the helicopter when it went down off Blacksod Mayo.
Dara spent years as a pilot with Waterford Coast Guard.
Waterford Minister of State John Halligan got to know Dara during her time in the Deise. He said, "I'm deeply upset and saddened to have heard the news yesterday of the tragic events that have taken place.
I'm particularly saddened at the loss of Dara Fitzpatrick, whom I became to know very well.
When I was mayor of Waterford she led a delegation to City Hall called Rescue 117, and that was the reception I gave.
Also I was privileged to have been taken on a tour of the coastline in thge air rescue helicopter with Dara on board."
Deputy Halligan went on to say, "what struck you from the first moment you were in her company was how utterly dedicated she was, both to her own work and also to water safety.
Dara was an inspiration to the many school children to whom she gave safety talks, particularly young girls who were considering a career in the industry.
My deepest condolences to her family, friends and her colleagues at the Irish Coast Guard, she is a great loss and will be sorely missed."
Meanwhile Jim Griffin from the Irish Coast Guard in Dunmore East says she was an exceptional pilot.
"You could take her judgment and trust it, just everything about Dara and the cooperation she got from her colleagues, like I suppose she was really in a male dominated role but as the head pilot for 20 years in the Coastguard, there's nothing you can't say about Dara that just personified everything that she stood for."
Joan Bowe from Dunmore East Coast Gaurd worked with Captain Dara Fitzpatrick when she was based in Waterford.
She says she was a great person.
"If you speak to anybody about Dara, you only had to met Dara once, to know that she was just a lady.
That's probably everybody's description of her.
She was so kind.
Such an inspiration really, an inspiration to everybody who met her."