Art is forged on part of flight (5)
I believe the answer is:
stair
'part of flight' is the definition.
(as in a flight of stairs)
'art is forged' is the wordplay.
'forged' indicates an anagram.
'art'+'is'='artis'
'artis' anagrammed gives 'STAIR'.
'on' is the link.
(Other definitions for stair that I've seen before include "single step in a series" , "that's between levels" , "section of flight" , "Step in house" , "Indoor step" .)