Rain shower, it’s wrecked suitability for flying (13)
I believe the answer is:
airworthiness
'suitability for flying' is the definition.
(quality of being airworthy)
'rain shower it's wrecked' is the wordplay.
'wrecked' indicates an anagram.
'rain'+'shower'+'its'='rainshowerits'
'rainshowerits' is an anagram of 'AIRWORTHINESS'.
(Other definitions for airworthiness that I've seen before include "being fit to fly" , "high flyers need it" , "requirement for flight" , "flying certificate?" , "Condition for taking off" .)