Section of flight from prison circling entrance to Alcatraz (5)
I believe the answer is:
stair
'section of flight' is the definition.
(I've seen this before)
'prison circling entrance to alcatraz' is the wordplay.
'prison' becomes 'stir' (informal term for prison).
'circling' indicates putting letters inside (circling can mean going around or containing).
'entrance to' indicates taking the first letters.
The initial letter of 'alcatraz' is 'a'.
'stir' enclosing 'a' is 'STAIR'.
'from' is the link.
(Other definitions for stair that I've seen before include "something of a case" , "one on the way up" , "Bit of a flight!" , "One step of a flight" , "Tread and riser" .)