It's emerged the Air Corps were initially asked to provide top rescue cover, before the missing Coast Guard Helicopter Rescue 116 was sent on the mission.
The Defence Forces confirmed they couldn't provide an aircraft outside of normal hours, because they didn't have the experienced personnel readily available.
Yesterday, a ping from the black box of Rescue 116 was detected by the search team.
The discovery of the signal means teams now have a location they can search for the voice recorder, and will send divers down as soon as it's safe to do so.
Jurgen Whyte with the Air Accident Investigation Unit says it's a major development:
"It's hugely significant. Other investigation authorities have spent months trying to do the same thing. We've been very lucky that within 36 hours we have picked up what is a signal. What that means is that the recorder has activated its beacon and we are using sophisticated equipment to home in on the signal itself."
A major search operation is continuing to try and locate the three missing crew members from the Coast Guard helicopter.
Captain Dara Fitzpatrick has so far been the only person recovered after it went down off the Mayo coast in the early hours of Tuesday morning.
She passed away later in hospital. Meanwhile the search operation for the 3 missing crew members continues.
President Michael D. Higgins has led tributes to Captain Fitzpatrick and said it marked a dark day in the history of the Coast Guard. He added: "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."
Dara's sisters Niamh and Orla have taken to Twitter:
My brave sister Capt Dara Fitzpatrick lost her life in #Rescue116 crash. We are devastated. Please pray for recovery of 3 remaining crew.
— Niamh Fitzpatrick (@NFitzPsychology) March 14, 2017 Her sister Orla also paid tribute:
Me & my gorgeous sister Dara...we'll miss you forever & love you always #RIPDara #Rescue116 pic.twitter.com/yIfFDlztU2
— Orla Fitzpatrick (@ofitzp) March 15, 2017
4 crew were on board the Dublin based Rescue helicopter when contact was lost just before 1am on Tuesday and no distress call was received from the aircraft.
It had been helping another helicopter to airlift a crewman off a fishing vessel when it disappeared from radar screens.
