Section of flight starts to surge through sky (5)
I believe the answer is:
stair
'section of flight' is the definition.
(I've seen this before)
'starts to surge through sky' is the wordplay.
'starts to' indicates taking the first letters.
'sky' becomes 'air' (I've seen this before).
The initial letters of 'surge through' is 'st'.
'st'+'air'='STAIR'
(Other definitions for stair that I've seen before include "this could get one down" , "Component of flight" , "Support on which to step" , "One of a flight of steps" , "A step on the way up or down" .)