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Why are some airports disqualified for use as an alternate (as listed in a approach procedure for that airport (A N/A)), when there is a provision in part 91 that an airport without an instrument procedure can be used if descent from MDA and under basic VFR conditions are expected using the 1-2-3 rule?

Example: I19 (Greene Co. Airport near Dayton, OH) has a disqualification (A N/A) listed in the procedure. Yet 11 miles away, I73 (Moraine) has no procedures and as I know it there is no specific disqualification. Albeit, you could only use Moraine for an alternate if descent from MDA and under basic VFR is forecast for the area.

So, why can you not use Green Co. if descent from MDA under basic VFR would be possible?

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    $\begingroup$ Welcome to aviation.SE! Does this question help? The procedure is not authorized for alternate purposes, not the airport. $\endgroup$
    – Pondlife
    Commented Jun 30, 2020 at 21:14

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There is a little bit of a misunderstanding in your premise. There is a difference between an alternate airport and a diversion airport. An alternate airport is your listed optional destination for the purposes of filing a flight plan. A diversion airport is the airport to which you head when you can not land at your original destination. They may be one in the same. For instance, when you divert to your alternate airport.

It is not that the airport can not be used as an alternate. It is that the approach can not be used to qualify the airport as an alternate. You can not use the standard precision approach, standard non-precision approach, nor non-standard approach alternate minima. You can, however, use the VFR weather minima to qualify the airport as an alternate. That means that both I19 and I73 are treated the same when filing. This is for filing purposes only.

Once airborne, the situation changes. If the weather or any other circumstance dictates a diversion to airport I19, you can use the procedure to shoot an approach down to the IAP minima regardless of if you filed it as an alternate or even if it qualified as an alternate when filing. Therefore, you could possibly effect a landing at I19 in IMC, but not at I73 in IMC. You could divert to either one in VMC. Even if your filed alternate were an entirely different airport.

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    $\begingroup$ I might consider emphasizing that if you go lost com ATC will expect you to go to your filed alternate. Seems obvious, but I have seen arguments about this... $\endgroup$
    – Michael Hall
    Commented Jul 3, 2020 at 20:37
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    $\begingroup$ @MichaelHall - True. I would even argue that an IFR plan is primarily to allow ATC to know where to expect you. Especially during NORDO. That makes your alternate your first (and second if filed) option when you lose Comms and your original destination is unavailable or unsafe. If you are currently VMC when you lose Comms, landing somewhere else is still an option. Just make sure you notify ATC as soon as practicable. $\endgroup$
    – Dean F.
    Commented Jul 3, 2020 at 21:03
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    $\begingroup$ I don't think this answer is 100% correct. For example, if the airport has IAPs and all of its IAPs are listed as "A NA" then you can't use that airport for filing purposes as an alternative. Yes, 91.169's provision for a VFR decent from MEA but that only applies to airports with NO IAPs. I do think this is a bit nonsensical but that is how I read the FARs. Of course, once you are air born you can fly to whatever alternative you want! $\endgroup$
    – pisymbol
    Commented Jul 19, 2021 at 14:25
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    $\begingroup$ In the US, at least, ATC doesn’t have ready access to your filed alternate. The point of the alternate is to force you (the pilot) to find at least one place you are nearly certain to be able to land if needed, and ensure you have enough fuel to get there. $\endgroup$
    – StephenS
    Commented Nov 29, 2021 at 0:15
  • $\begingroup$ @StephenS Agreed. My TraCon friend says ATC does not receive your filed alternate as part of their data stream. Lost Comms after going missed or when first intended airport is not viable is not a situation expressly defined in faa.gov/air_traffic/publications/atpubs/aim_html/… TraCon friend also said they REALLY want a NRDO plane out of the system, so finding a VFR option is highly desirable. If it was solid IMC or a solid deck beneath me, I probably would go to my filed alternate, having already planned and reviewed it. Less stress... $\endgroup$
    – Catapult
    Commented Jul 30, 2022 at 22:49

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