I think at the time (1981?) it was thought the DASH 7 could go anywhere
where the Twotter could, but St Mary's then, was found to be out of limits - I think there was one test fight with Brymon. Capt Harry Gee iirc. But they were not happy.
Edit
re DASH 7 performance and ISC
please see thread here for more correct forum
Scilly Isles Route
Thanks