Two-directional navigational aid (5)

I believe the answer is:

radar

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

I don't understand the rest of the clue.

(Other definitions for radar that I've seen before include "Palindromic tracking system" , "Gluttony" , "A help in locating" , "It can locate things in the dark or fog" , "System for pinpointing ships and aircraft" .)

I've seen this clue in The Globe and Mail.

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