Find out in case train crashed (9)
I believe the answer is:
ascertain
'find out' is the definition.
(synonyms)
'case train crashed' is the wordplay.
'crashed' is an anagram indicator.
'case'+'train'='casetrain'
'casetrain' with letters rearranged gives 'ASCERTAIN'.
'in' acts as a link.
(Other definitions for ascertain that I've seen before include "Prove" , "Find out for sure, determine" , "Cartesian (anag)" , "settle" , "Discover" .)