My memory is of a ‘legacy’ route, initially created by Irish Helicopters to be used by the Bo105 servicing the Irish Lights contract. It’s purpose was to provide a ‘safe’ route between Blacksod and Blackrock Island, intended to be used for transit between both locations in poor weather conditions, subject to Day VFR regulations. At the time, flights at night could not be operated under VFR.
The ‘plate’ showed a magnetic track/reciprocal track and distance between each point on the route overlaid on the appropriate section of a VFR navigation chart. Each reference point was abeam an identifiable land feature. It pre-dated GPS and was flown on a time elapsed / dead reckoning basis. It was operated single pilot and without incident over the years although each pilot would have been very familiar with both the route and the topography of the area. It was never intended for navigation west of Blackrock Island.
Let us all remember that 4 people needlessly lost their lives in this accident. If it serves only 1 purpose, that is, if it causes you to examine more closely, to question and re-evaluate EVERY approach you consider making in ‘undetermined and unknown’ areas / conditions, then their sacrifice will not have been in vain.