DUBLIN -- A female pilot died Tuesday in an unexplained rescue helicopter crash off the coast of Ireland.

Capt. Dara Fitzpatrick, 45, was found in the Atlantic Ocean around six hours after the helicopter vanished without sending out a distress call. She was later pronounced dead. Her three colleagues are missing and feared dead.

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

A major search off the County Mayo coast was launched after the Irish Coast Guard helicopter crashed overnight.

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Fitzpatrick, from Dublin, had been involved in search and rescue missions for over 20 years.

Eugene Clonan, acting director of the Irish Coast Guard, said hopes of finding the other three personnel were fading.

The search involves an Irish naval vessel, two lifeboats, five private trawlers, two helicopters and an army surveillance plane.

The Dublin-based Sikorsky helicopter disappeared from radar as it arrived in Mayo to support a second helicopter that was rescuing an ill fisherman aboard a British trawler.