Type of crack high flyers might have? (8)
I believe the answer is:
hairline
'type of crack' is the definition.
(as in a hairline crack)
'high flyers might have?' is the wordplay.
'high' becomes 'h' (abbreviation).
'flyers might have?' becomes 'airline' (an airline flies).
'h'+'airline'='HAIRLINE'
(Other definitions for hairline that I've seen before include "Very narrow opening" , "(Very fine) crack or fracture" , "Barnet's border" , "A very narrow crack, a little hirsute?" , "area on the outskirts of Barnet?" .)