Ace in scariest turbulent flight (9)
I believe the answer is:
staircase
'flight' is the definition.
(a flight of stairs)
'ace in scariest turbulent' is the wordplay.
'ace' becomes 'a' (abbreviation).
'in' is an insertion indicator.
'turbulent' indicates an anagram.
'scariest' anagrammed gives 'staircse'.
'a' going inside 'staircse' is 'STAIRCASE'.
(Other definitions for staircase that I've seen before include "Flight of steps" , "It's Caesar (anag.)" , "Set of steps" , "part of the mansion?" , "Way between floors" .)