Navigational aid for getting back again (5)

I believe the answer is:

radar

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'navigational aid' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for radar that I've seen before include "Aircraft detection system" , "System for detecting objects with radio waves" , "Range-finding apparatus" , "It can locate things in the dark or fog" , "Position detector using radio wave pulses" .)

I've seen this clue in the Evening Standard.

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