Current navigator's device needs to start (6)
I believe the answer is:
extant
'current' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for extant that I've seen before include "Still living" , "Still existing, not obsolete" , "Not destroyed or lost" , "still alive" , "Net tax still existing, not gone" .)