Regarding weather minima ... in the old days ISC had a minimum RVR (RUNWAY Visual Range) of 1,500m yet with a runway of a mere 600m (ish) 1,500m was barely practicle.
Back in the Brymon days EXT had a habit of attracting fog on the approaches yet the Brymon Twotter(s) would be overhead looking down on a crystal clear airfield ... correct me if I am mistaken but I'm of the impression that fixed wing and rotary wing have the same minima's to adhere to.
And let it not be forgotten that it was 1983 that BA Helicopters lost an inbound to ISC with a significant loss of lives, Brymon Twotters hadn't yet managed to get in to ISC that day, a chopper tried it and the rest is history ... R.I.P.