I know it shouldn't happen but in case it happens for whatever reason, what is correct procedure to save the day. I mean the case that the aircraft is turning but it gets to the wrong side by, let's say, one, maybe two deg, so the pilot or autopilot has to make the correction and "fly back" to LOC.

I guess the ATC won't be happy, due to separation, protected areas of parallel runway or so.

But how to solve that? Can the aircraft fly back to LOC on its own, still asume it is within LOC deviation scale and we can see the diamond? Should they inform ATC that they will be on the wrong side for a while? Do they have to be vectored back to ILS again? I ask specificaly for this because I was told so but it seems to be quite ridiculous to issue a new vectoring for few seconds because before it will happen the aircraft will be already turning to LOC and it will be useless.

  • $\begingroup$ As a controller—if I issue an egregiously late turn, I will take responsibility and either issue a vector back toward the LOC or a re-sequence if necessary. If the turn is only slightly late, I expect the pilot to correct silently. $\endgroup$
    – randomhead
    Sep 3, 2022 at 0:28
  • $\begingroup$ There was an issue in Toronto some years ago where some sort of Loc antenna issue would cause Air Can Jazz CRJs to start to capture, then spontaneously reverse and start to turn away. The pilot would have to go into HDG mode to correct and recapture, or if too far off, disconnect A/P and hand fly to keep in lateral limits. I don't remember what the actual root cause was. $\endgroup$
    – John K
    Sep 3, 2022 at 3:39
  • $\begingroup$ @randomhead As I said, that turn was a bit late. Or I would call it a bit late, still visible on instruments where the LOC is, known deviation about 1 degree or 1,5 degree. So on ILS with final apch crs 180° the aircraft would be eg. 181-182° on 11 NM from RWY. Would you consider this as too much? The AC was turning back to LOC on its own. $\endgroup$
    – pzag
    Sep 3, 2022 at 6:39
  • $\begingroup$ I would expect the pilot (or autopilot) to silently intercept the localizer in that case, and probably even up to 5-10° overshoot. But it's a gray area; is the a/c 5° too far or 10°? Is the a/c type an F18, B752, LJ75, or P28A? Is it a student pilot training flight or commercial passenger flight? Are they 3 miles from FAF or 13? $\endgroup$
    – randomhead
    Sep 3, 2022 at 11:00
  • $\begingroup$ @randomhead It is something like B737/A320, 2-3 NM from FAF and no more than 3°. I know it is grey area. i was curious about some real life opinions. Thanks a lot. $\endgroup$
    – pzag
    Sep 3, 2022 at 15:41

1 Answer 1


If you are instructed to intercept the localizer and/or cleared for the approach, that means you need to stay established on the localizer, i.e. keep the needle at leas than full deflection.

It doesn’t matter whether the needle is deflected left or right. As long as it doesn’t hit either peg, you are still established and can maneuver as needed to get (and keep) the needle centered.

If you do hit the peg on either side, that’s a missed approach; tell ATC immediately. Depending on where you are and other traffic, they may vector you back on or take you out and back for another try.

There are special rules for parallel approaches, but you should not be getting (or accepting) those without the proper training and authorization.


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