Arson using navigation aid (5)
I believe the answer is:
sonar
'navigation aid' is the definition.
(I've seen this in another clue)
'arson using' is the wordplay.
'using' indicates anagramming the letters (the letters used in a different way).
'arson' is an anagram of 'SONAR'.
(Other definitions for sonar that I've seen before include "Underwater detection device" , "Underwater location equipment" , "System to locate underwater objects" , "Undersea sensing system" , "Underwater echo sounder" .)