'Catastrophic failure' caused Irish Coast Guard helicopter crash
Parents pay tribute to 'beautiful' daughter as probe begins into helicopter's electrics
The probe into the loss of Coast Guard Rescue 116 helicopter is currently centring on whether "electrical failure" on the helicopter caused the crash.
Investigators have also looked into the possibility the helicopter could have collided with the lighthouse at Blackrock, six miles off the coast of Mayo.
However, this theory is now discounted as there was no evidence of a collision with the rock five miles off the coast and there was no wreckage around the lighthouse.
"There was no paint or debris on the lighthouse. There are 100 theories going around," a senior investigation source said.
The full-scale search is honing in on an area near the lighthouse where the black box is now believed to be located.
The crash claimed the life of pilot Captain Dara Fitzpatrick, while her crew of three, Ciaran Smith, Mark Duffy and Paul Ormsby, are still missing.
The pilot's sister, Niamh Fitzpatrick, described how she had adopted her son at the age of one week old and managed to juggle weaning, potty-training and early child-rearing with a job that was "not nine to five."
She said Dara was "a wonderful mother" whose "happy, contented and unstressed" three year old son is a tribute to her.
"Professionally she was a kind and lovely girl but I also want to say what a great mother she is. That she has a little boy who is handling this," she said.
Her parents described Capt Fitzpatrick as being "beautiful, inside and out".
They spoke of how they stayed with her last night to make sure she wasn't alone. "She always told us if anything ever happened, she never wanted to be left alone, so when we arrived down here last night at half 10 we decided we would do shifts.
"We kept our promise to her."
Officials believe there was no mayday call because of a "catastrophic failure" on board.
"It takes two seconds to press the mayday button. The fact they did not press the button shows the suddenness of the impact. They only had seconds before the crash," a source said.
Coast Guard officials also point to the impeccable safety record of Captain Fitzpatrick.
"She would never leave a stone unturned," they added.
Yesterday, an underwater signal was successfully detected from the black box of the downed Rescue 116 Sikorsky S-92A helicopter shortly after 4pm.