The Coast Guard has confirmed that a female crew member has died after a helicopter went missing off the west coast overnight.
Captain Dara Fitzpatrick died in hospital after being recovered from the water earlier today.
Gerry O’Flynn from the Irish Coast Guard confirmed that Dara was the most senior pilot with CHC, who were contracted to operate helicopter Rescue 116 when it went down last night.
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Three other crew members who were on board are still missing, and a major search operation is underway off the Mayo coast, around six miles west of Blacksod.
There are currently five fishing vessels assisting the operation, was well as two Coast Guard helicopters, the LÉ Roisín, and an Air Corps Casa plane.
The Coast Guard say debris was also found spread over a wide area.
Contact was lost with the four crew helicopter at around 1.00am on Tuesday morning.
The Dublin-based R116 was providing safety and communication support - known as Top Cover - to another helicopter involved in the medical evacuation of a crewman requiring urgent medical attention.
"A woman of extraordinary courage"
Transport Minister Shane Ross said "today is one of the darkest days suffered by our brave, committed emergency services".
He told reporters that no resources will be spared in the search for the missing crew.
Minister Ross said: "On behalf of my department and me, I would like to extend my sympathies to the family, friends and colleagues of Capt Dara Fitzpatrick - a woman of extraordinary courage and professionalism who made the ultimate sacrifice in the service of others... the young mother whose loss will be hugely felt."
President Higgins paid tribute to Capt Fitzpatrick "on behalf of the Irish people".
He said: "We are all grateful for the courage, resolution and exemplary commitment to the aims of the Coast Guard that Captain Fitzpatrick and her colleagues have consistently displayed.
"My thoughts are with her family at this difficult moment and also with the families of the missing crew."
Enda Kenny, speaking in the US, said: "On behalf of the Government, I want to issue our deepest sympathy in respect of the family of Capt Dara Fitzpatrick."
Dara Fitzpatrick had been with the search and rescue service for more than 20 years.
She made Irish aviation history three years ago when she flew the first all-woman mission for the service.
Dun Laoghaire Coast Guard paid tribute to Capt Fitzpatrick, describing her as an 'inspiration to many young people':