As Crab and one or two others have posted, it seems very strange for the aircraft to have been anywhere near Blackrock lighthouse. It is 10nm further on from Blacksod and there was pretty much flat sea in between. Why on earth would you want to go to a 300ft elevation rock to let down? Doing a let down over the sea say 2nm east of Blacksod, into wind, would have been far more logical, assuming poor weather. So it seems to me hard not to believe they misprogrammed the FMS and thought Blackrock was Blacksod. But then why didn't they see from the moving map that they were approaching a rock 10 miles off the coast and not the eastern side of a mainland peninsular? A £700 iPad with a moving map programme (as many of us use as back up) would have made that obvious.