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6 Answers

Visibility

Asked by: 11497 views FAA Regulations

Any logical reason why RVR is measured in statute miles and not measured in nautical miles? I realize that if a airport has RVR equipment that the approach mins. will be in RVR format. But is there a situation where a airport has RVR equipment but the approach mins. are in nautical mile format? Thank you for the feedback.

6 Answers



  1. Derek Schwalenberg on Oct 06, 2013

    RVR is actually expressed in feet. Although typically weather reports are given in statute miles.

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  2. John D Collins on Oct 06, 2013

    All visibilities are expressed in SM, none in NM. RVR is expressed in feet. The highest RVR is 6000 feet. If an approach requires a visibility greater than 6000 feet, it will be expressed in SM. There is a conversion table that translates RVR to SM, but don’t interpolate, if a value of RVR falls between two SM equivalents, you must use the higher value. RVR won’t be reported if above 6000 feet or 1 SM, in which case all reports will be SM.

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  3. Kris Kortokrax on Oct 06, 2013

    Dan,
    Consider that if visibility minima were expressed in nautical miles, if the minimum were 1/2 mile, you would need 3038 feet of visibility to land. In statue miles, 1/2 mile is 2640 feet (about 400 feet less visibility).
    There is a benefit to expressing visibility requirements in statute miles. You can legally land in worse weather than if it were expressed in nautical miles.

    John,
    If I didn’t know better, I would assume from your post that 6000 feet equates to 1 SM. The AIM table shows 5000 RVR for 1 SM.

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  4. Dan Chitty on Oct 06, 2013

    Excellent points.Much appreciated.

    To clarify, is visibility for ATIS in statute miles ( I could not locate in FAA books but please let me know source)? I assume yes since METARs are pulled from ATIS broadcasts. If in statute miles, then why are approach plate mins. in nautical miles? I am trying to understand why TERPS does not use statute miles on approach plates if this is true.

    Let me know your thoughts.

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  5. Kris Kortokrax on Oct 06, 2013

    Who said that minima on approach plates are expressed in nautical miles?

    Does it make sense to you that approach plate minima would be given in nautical miles and that the prevailing visibility would be given in statute miles requiring you to do a conversion?

    Come on, think a little bit.

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  6. Dan Chitty on Oct 06, 2013

    Kris,

    I just realized that I completely misread the legend in front of the approach plates. I have been away from the IFR world for a long time and am beginning to realize that being absent from the IFR world for a long time is not to my advantage.

    Thank you for the feedback and thanks to all for your comments.

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