Captain Dara Fitzpatrick has died a hero on a mission to aid another coast guard unit off the coast of Mayo.
The devastating flight left Dublin at 11pm last night and went off radar at 1am this morning.
Its wreckage was found this morning along with Dara in critical condition.
The search operation for the remaining three missing Irish Coast Guard crew members is to continue overnight.
The three other crew on board have been named as Chief Pilot Mark Duffy and winchmen Paul Ormsby and Ciarán Smith.
The air search has been scaled down until first light but hundreds of emergency personnel are said to be working to find the missing crew.