Frank is allowing access (4)
I believe the answer is:
open
I believe this clue is a double definition.
'frank' is the first definition.
(synonyms)
'allowing access' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for open that I've seen before include "Unrestricted; ready for business" , "golf contest" , "with no clear favourite" , "'Frank, not secret (4)'" , "Allowing entry and exit" .)