The Irish Aviation Authority has said an Air Corps Pilatus PC9 aircraft has crashed at Crumlin East near Cornamona in Connemara, Co Galway.
The aircraft carrying a flight instructor and cadet were part of a flying training exercise of three aircraft that left Casement Aerodrome, Baldonnel at 5.45pm.
The accident is believed to have happened shortly after 6pm this evening.
The two other aircraft have safely returned to Galway airport.
A number of local people reported seeing the aircraft in difficulty and preparing to make an emergency landing.
An Air Accident Investigation team from the Air Corps and Department of Transport have been dispatched to the area.