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I've watched a few videos on youtube where the pilot flies an Instrument Landing System (ILS) approach to the minimum allowed altitude before establishing visibility of the runway (MDA or minimums).

What I'm wondering though is what constitutes "runway in sight"? I mean, in some cases that's going to be obvious (ie., you can see the runway clear as day long before minimums.) But what if the cloud base is right at minimum and you can kind of see outside, but not in every direction (ie. maybe it's slightly clearer just a bit to your left than to your right.)

What do you have to see to consider the runway in sight? The whole runway? Just the lights? Just the approach lights? Just the VASI/PAPI? Would it be considered enough if, perhaps, you could see a windsock that you know is close to the runway? Or perhaps there's a cross street right before the runway that you're very familiar with, would that work? What would be considered "runway in sight" so that you can continue the approach rather than going missed?

Note/Clarification: The general rule, of course, is "when in doubt, go missed". So in a lot of ways this question is academic. What I would love, though, is a two part answer, with one part that has the exact rules (per the FAA) and the other with some common sense guidance on when to continue and when to go missed.

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From FAR 91.175:

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

(ii) The threshold.

(iii) The threshold markings.

(iv) The threshold lights.

(v) The runway end identifier lights.

(vi) The visual approach slope indicator.

(vii) The touchdown zone or touchdown zone markings.

(viii) The touchdown zone lights.

(ix) The runway or runway markings.

(x) The runway lights

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    $\begingroup$ Any chance you could expand on 91.175(3), I didn't know it could differ for Cat II and Cat III. $\endgroup$
    – Jae Carr
    Commented Sep 8, 2016 at 0:05
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    $\begingroup$ @JayCarr I think that that statement just means, Cat 2 + 3 have their own rules, don't use these general rules there. For Cat III, "fail operational" criteria & an Alert Height give a whole new set of "operations below DH" rules, or maybe the lack of a DH at all. Cat II rules that I'm familiar with aren't especially different from these, but are published in their own OpSpec, separate from Cat I rules. $\endgroup$
    – Ralph J ♦
    Commented Sep 8, 2016 at 23:21
  • $\begingroup$ Well, if you could just drop that explanation into your answer... that would go along way in making this answer correct. Though I was hoping for some common sense guidance as well (if there is any to be had), about how much of any of the listed identifiers you need to see to really consider going. It just feels like there are many things that could possibly be mistaken for things on that list. I guess mostly what I'm asking for is "how certain is certain enough?" $\endgroup$
    – Jae Carr
    Commented Sep 8, 2016 at 23:27
  • $\begingroup$ On second look, our book says that the last two points (runway, its markings, its lights) are Cat I only. For Cat II or III it's necessary to have the touchdown zone of the runway or its markings or lights (or any of the other things) in sight. Seems like a strange case when you could see "the runway" but not "the touchdown zone" at 50' or 100', but that's the FAA for you. Why the VASI isn't similarly "Cat I Only" is entirely beyond me! $\endgroup$
    – Ralph J ♦
    Commented Sep 8, 2016 at 23:33
  • $\begingroup$ Huh, interesting... But could you be persuaded into editing it into the answer? The comments tend to disappear sometimes around here... $\endgroup$
    – Jae Carr
    Commented Sep 8, 2016 at 23:35

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