Practical American fuel tanks (6)
I believe the answer is:
'practical' is the definition.
(similar in meaning)
'american fuel tanks' is the wordplay.
'american' becomes 'us' (abbreviation for United States).
'tanks' is an anagram indicator (tank can mean to fail or go wrong).
'fuel' is an anagram of 'eful'.
(Other definitions for useful that I've seen before include "Advantageous - efficacious" , "Advantageous; very able" , "Practically helpful" , "Beneficial" , "Convenient" .)