Aid in navigating back again (5)
I believe the answer is:
radar
'aid' is the definition.
(I have seen 'Navigational aid ' mean 'radar' so perhaps 'aid' could also mean 'radar')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for radar that I've seen before include "Technique using beam" , "System for detecting objects with radio waves" , "A help in locating" , "System for locating distant objects" , "Measuring device that locates distant objects" .)