The Rescue 116 helicopter is believed to have crashed into the sea not far from Blackrock Lighthouse off the Mayo coast.
Built on a rock outcrop located at sea some 12km from Blacksod Head, the lighthouse was designed to warn shipping off one of the most notorious stretches of coastline in Europe.
Several Spanish Armada vessels were wrecked in waters between Donegal, Mayo and Galway in the 16th century.
The actual lighthouse stands some 16 metres in height but, when combined with the height of the rock outcrop on which it is built, the overall height above sea level is some 84 metres.
Blackrock Lighthouse was ordered in 1857, built in 1863 and became fully operational on June 1, 1864.
Its light, which flashes white to sea and red to land, is visible for almost 34km.
The Commissioners of Irish Lights (CIL), which operate the facility, will be one of a number of agencies helping the Air Accident Investigation Unit with its investigation into the tragedy.
It is now expected to task its support vessel, ILV Granuaile, to the scene.
The ship is equipped with a heavy lift crane, which helps in salvage and recovery operations.
CIL official Captain Robert McCabe confirmed that all aids to navigation on the lighthouse were operational.
Blackrock Lighthouse was one of the first in Ireland to be converted to automated rather than manned operations.
This was due to its offshore location and the demands on lighthouse keepers, particularly in the harsh winter months.
It became fully automated in 1974.
Blackrock has since been fully modernised with the most modern LED lighting and aid-to-navigation systems.
For almost 150 years, the primary aim of Blackrock Lighthouse has been to warn shipping off dangerous local rocks and guide vessels towards the shelter of Blacksod Bay.
Blackrock Lighthouse was previously associated with an aviation incident, albeit of a different kind.
In August 1940, part of the lighthouse was damaged when it was hit by stray gunfire from a German bomber which had been attacked by a merchant vessel located passing by the rock.
The aid-to-navigation systems on Blackrock Lighthouse are monitored via telemetry links from the Commission of Irish Lights headquarters in Dublin.