It concluded that the probable cause was that while the helicopter was flying towards its intended landing spot at 200 ft, at night, in poor weather, the crew was unaware of the presence of a 282-foot obstacle in their flight path.

During the evening of 13 March 2017, the Malin Head Coastguard took a call from the captain of a fishing boat 250 kilometres (130 nmi) off the west coast, who reported that one of his crew had suffered an accident in which he had lost part of his thumb.

[10](pp13-16, 310) The alarm was raised by the crew of the lighthouse when the helicopter failed to arrive as expected, prompting the Marine Rescue Coordination Centre (MRCC) in Dublin to declare an emergency.

[10](pp127-129) Rescue 115, the Shannon-based Coast Guard helicopter, was dispatched to the area to aid in the search for the other three crew members, along with a CASA CN-235 maritime patrol aircraft from the Irish Air Corps.

The vessel is equipped with a dynamic positioning system which allows it to operate in difficult sea conditions, cranes capable of hoisting recovered wreckage and a helicopter platform.

[19] On the afternoon of 15 March, a signal transmitting from the helicopter's multi-purpose flight recorder[a] was detected by a team from the Irish Marine Institute using USBL equipment from a local fishing[citation needed] vessel.

The use of the fixed-wing CN-235 is generally considered preferable in this role because it can reach the scene quicker and remain on station for longer than a helicopter can,[36][37] but on the night of 13-14 March this was not possible because of a staff shortage in experienced and trained personnel which made it unable to operate an "out-of-hours" roster.

[40][41] At 1:45 am, an hour after last contact from Rescue 116, the Coast Guard made an emergency request for assistance to the Air Corps to help search for the missing SAR helicopter.

The Air Corps activated its recall plan and 3 hours and 45 minutes after the Coast Guard's initial request for top cover, a CASA CN-235 maritime patrol aircraft was airborne.

[45][clarification needed] The AAIU found no mechanical anomalies from the flight recorder data, and therefore no additional safety actions were required on similar helicopter types.

[47][better source needed] Just three weeks before its fatal crash, Rescue 116 with the same four crew members appeared briefly in the 1st episode of 3rd season of the Irish TV show Paramedics.