With my trained Air traffikers ears ( I talk to these guys on a daily basis) they definately say their intention is to refuel at Blacksod.
I am guessing that most of the navigation is done by the crew in the back of the cab using all the bells and whistles available to them. And I understand that is some pretty good kit with a map display going down to Ordnance Survey quality. So why end up at Black rock when they think they are going to Blacksod?
I am certain all will be clear once the contents of the CVR are revealed.