Offshore alternates
I remember when I first started on the North Sea with the old AS330 Puma that had an offshore alternate facility. It was essential at Teeside for the Ekofisk otherwise there was no other way you could get there. One day at Aberdeen the whole of Scotland was socked in but I departed because I could find the runway and I had nominated the Claymore as my take-off diversion. It must have been legal because my chief pilot told me to do it