Niamh Fitzpatrick took to Twitter on Saturday morning to mark the anniversary of the last time she saw her sister alive.
The psychologist and author reminded her followers to keep their loved ones close as she paid tribute to Dara online.
She said: “Today is the anniversary of the last time I saw Dara alive, heard her voice, saw her smiling face. 32 hours later she was dead.
“That ordinary conversation between us, now an extraordinary moment in our lives together.
“Spend time with those you love. It’s all we’ve really got.”
Captain Fitzpatrick lost her life alongside fellow Irish Coast Guard crew members, Captain Mark Duffy, winch operator Paul Ormsby and winch man Ciarán Smith when their helicopter crashed into Blackrock Island, off the north Mayo coast in 2017.
They had been providing assistance to another coast guard helicopter called to airlift a fisherman from a trawler.
While the bodies of Captain Fitzpatrick and Captain Duffy were recovered in the days following the tragedy, the bodies of their colleagues remain lost at sea.
Achill Island Coast Guard also paid tribute to their colleagues five years after the tragedy with a social media post.
Taking to Facebook, a spokesperson said: “On this night, five years ago, a vessel some 141 nautical miles off our west coast made a call for help.
“Two Irish Coast Guard helicopters answered that call. Rescue 118 from Sligo and Rescue 116 from Dublin.
“At 01:46 Rescue 116 crashed with the loss of its four crew.
“Captain Dara Fitzpatrick, Captain Mark Duffy, winch operator Paul Ormsby and winchman Ciarán Smith were four of our finest. We will always remember them. Go Mairidís Beo.”
Limerick Fire and Fire shared their own message of remembrance online, writing: "Today we remember the crew of Irish Coastguard Helicopter, Rescue 116, who perished after they crashed at Blackrock on this in day in 2017.
"Our thoughts are with the families, friends and colleagues of all who died. May they rest in peace."
And Irish Lifeboats praised the "courage" of the Rescue 116 crew: "On this night five years ago, four Irish Coast Guard Search and Rescue helicopter crew #Rescue116 set out on a mission and they never came home.
"Please take a moment to remember their courage and service and to remember their families and Irish Coast Guard family. #GoneNeverForgotten"