An aircraft is to track from NDB A to NDB B. The RMI of NDB B reads 357 & RMI of NDB A reads 177. The aircraft is:

A: Drifted left of track
B: Drifted right of track
C: On track

I think it is 'C' but the answer is 'A' can someone explain this?

  • 4
    $\begingroup$ Welcome to Aviation! Please edit your question to indicate why you think the answer is A so people can see where you've gone wrong and help correct your misconceptions. $\endgroup$
    – FreeMan
    Commented Jun 23, 2020 at 12:57
  • $\begingroup$ @FreeMan, he thinks it is C and he is correct. The published answer A in whatever reference he took this from is not right. And if this is from an FAA test question database it wouldn’t be the first wrong “correct” answer... $\endgroup$ Commented Jun 23, 2020 at 17:04
  • 1
    $\begingroup$ @MichaelHall thanks for your explanation and sorry for not being clear with the source. It's an answer that my friends noted. C is the right choice. $\endgroup$
    – user50189
    Commented Jun 28, 2020 at 6:08
  • $\begingroup$ If anyone else lands on this question here's an interesting tool to visualise NDB readings vs aircraft position: donpilot.com/interactive-ndb-tool . In this particular case you'd simulate the readings for both NDBs to figure out what your position is. $\endgroup$
    – Nick M
    Commented Oct 16, 2023 at 8:32

1 Answer 1


You are right, the correct answer should be C.

Those two bearings are reciprocals of each other. Being 180 degrees out from each other, the lines are parallel. Parallel lines never intersect, so the only way that you can be on both at the same time if is they are overlaid on the same track; I.e. a single straight line between the two points.

If you had drifted off course from a direct track between the two ground stations, the two bearing lines would be at angles to one another, and you would be at the point where they intersect.


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