The plane crash one never forgets (8)
'one never forgets' is the definition.
(supposedly, elephants never forget)
'the plane crash' is the wordplay.
'crash' indicates an anagram.
'theplane' is an anagram of 'ELEPHANT'.
(Other definitions for elephant that I've seen before include "bigger one from two continents?", "Large animal found in the plane?", "Trunk carrier?", "Trunked mammal", "Tusked mammal".)