A black box signal has been detected during the search for the remaining crew of a missing Irish Coast Guard helicopter off the west of Ireland.
Rescue workers have described the find as “significant” as mystery still surrounds what happened on the Sikorsky S92 which lost radio contact without any warning at around 12.45am on Tuesday.
Captain Dara Fitzpatrick, 45, was pulled from the Atlantic off the Co Mayo coast – around six miles (10km) west of Blacksod – deemed critically-ill but later confirmed dead.
She was the mother of a three-year-old son.
The other three crew, who have yet to be found, are chief pilot Mark Duffy from Dundalk, Co Louth, as well as Ciaran Smith and Paul Ormsby, both winchmen from north Co Dublin.
As a second day of searching was being wound down hopes had faded for the survival of anyone.
But the signal of the black box recorder could lead investigators to the bulk of the aircraft – which has yet to be located – and could hold vital clues as to the final moments of its doomed mission.
Gerry O’Flynn, of the Irish Coast Guard, confirmed a hydrophone being employed to try pick up the radio frequency of the black box was successful shortly after 4pm.
“A signal has been detected and we regard this as a very significant step forward in terms of progressing the search stage of this operation,” he said.
“So we’ve detected signals. The next stage will be to locate it.
“We’ve now begun the process of locating the exact position.”
It is understood the signal was detected in and around the Blackrock Lighthouse, about eight miles (13km) off Blacksod.
The black box transmits a signal underwater for 30 days.
The search operation is also using sonar equipment to try to locate the missing crew members while air and shore searches are ongoing.
Ms Fitzpatrick’s sister, Niamh Fitzpatrick, said her family is heartbroken but added “we have no regrets where Dara is concerned”.
“She lived her life to the full and did what she wanted to… she has a beautiful son,” she told RTE radio.
“They say it takes a village to raise a child and he has a village around him now who will raise him on her behalf.”
The Commissioner of Irish Lights ship, the Granuaile, and a second Naval Service patrol ship, the LE Eithne were also called on to join the flotilla of vessels involved in the operation.
Declan Geoghegan, of the Irish Coast Guard, said he was confident the main bulk of the missing helicopter will be located.
“The main frame, the engine and gearbox is still in the water. We should be able to find it, it is in just 40 metres of water,” he said.
“With the luck of God, they might be trapped in it.”
The Dublin-based helicopter crew was providing cover for another Coast Guard helicopter involved in an early-morning evacuation of a crewman needing urgent medical attention on a UK-registered trawler, approximately 150 miles (240km) west of Eagle Island in Co Mayo.
It had flown directly to the scene from the Irish capital, travelled around 10 miles (16km) out to sea, then turned back towards land to refuel.
There was no indication of any danger moments before it vanished, with the crew’s final transmission: “Shortly landing at Blacksod.”
Visibility was described as not good at the time.
When the helicopter failed to arrive, a Mayday signal went out and Coast Guard helicopters from Sligo and Shannon along with the Air Corps maritime patrol aircraft Casa were tasked to the scene.
They were joined by lifeboats from Ballyglass and Achill, the Naval Service’s LE Roisin ship and five local fishing vessels.
Officials from the Air Accident Investigation Unit are also at the scene carrying out a full investigation.
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