a busy cat

For the RNAV (GPS) RWY 17 approach at KSMN, why does it say "Helicopter visibility reduction below 3/4 SM NA."?

Looking at the LNAV, there is a 5 mile visibility requirement and if we cut that in half per AIM 10-1-2, wouldn't there be a 2 1/2 mile visibility requirement? If so, then a helicopter couldn't fly the approach with 3/4 mile visibility anyway.

  • $\begingroup$ I'm not entirely sure what your question is. $\endgroup$ Jun 8, 2017 at 0:53
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    $\begingroup$ @CarloFelicione -- his question's fairly simple actually: "why did the FAA put a note on the plate that has no effect in practice?" $\endgroup$ Jun 8, 2017 at 1:23
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    $\begingroup$ It does seem odd. My only thought is that perhaps some §135 operations could have authorizations that could allow them to use lower visibility minimums, apart from a prohibition like this. $\endgroup$
    – J Walters
    Jun 8, 2017 at 4:18
  • $\begingroup$ Can't an helicopter approach on a 350° course and then circle to land to RWY 17. In this hypothetical explanation, the 5 mile requirement wouldn't apply. $\endgroup$
    – mins
    Jun 8, 2017 at 18:16
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    $\begingroup$ AFAIK, the 3/4 SM restriction is there because of obstacles (presumably the tower between the MAP and the runway) but I have no idea why they printed it when the minimums are much higher anyway. My guess is it was included by default but the best way to get an answer might be to ask the FAA. We've done that before :-) $\endgroup$
    – Pondlife
    Jun 8, 2017 at 19:15

3 Answers 3


Helicopters may operate under special VFR when in flight visibility is less than 1 SM. Therefore, the approach can be flown at lower visibility than that published on the approach plate. However, the note must be published to further restrict these types of operations: "The procedure is annotated with 'Visibility Reduction by Helicopters NA.' This annotation means that there are penetrations of the final approach obstacle identification surface (OIS) and that the 14 CFR Section 97.3 visibility reduction rule does not apply and you must take precaution to avoid any obstacles in the visual segment."1


My understanding is that similar to the notation on the chart that "DME/DME RNP-0.3 NA, the helicopter notation (Helicopter Visibility Reduction less than 3/4 SM NA) is just a charting convention.

Even though it's obvious from the (non-helicopter) 5 mile min vis (reduced to 2.5 miles for helicopters), the issue of 3/4 SM is never relevant. The same goes for the "DME/DME RNP-0.3 NA, which is irrelevant also since in order to fly a RNP -0.3 approach (which an LNAV approach is), you must use a properly certified GPS system to achieve the RNP -0.3 performance accuracy (DME/DME RNP can never be used). I think both are just a charting convention.

This question has been asked before on another forum (can't remember which one) and this seemed to be the accepted most reasonable answer.


Remember that the helicopter visibility restriction also applies to IFR departures. under part 135, you can depart IFR without a takeoff alternate if you have the visibility to shoot the approach straight in, and all the equipment is working... this visibility can be cut in half unless it says helicopter vis reduction N/A.

So, looking at this approach plate alone would still not answer your question. But, if you look at the other VOR/DME B approach you can see that the required vis is 1.25sm vis. Helicopters would usually be allowed to cut that in half and therefore depart IFR without a takeoff alternate if the vis was .625sm vis.

I looked it up, but they seem to have removed the limitation as of me writing this. But I would be curious if they had that limitation on all of Lemhi's approaches in order to limit the IFR departure to 3/4sm.

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    $\begingroup$ Welcome to Aviation.SE! Could you provide some sources for your answer? $\endgroup$
    – dalearn
    Jan 4, 2020 at 21:32

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