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3 Answers

Are Published IFR Distances Actual or DME?

Asked by: 2131 views Airspace, Instrument Rating

Numbers enclosed in a "D" are DME distances, but what about the ones in squares? Are the distances published on an IAP without a DME actual distances or still DME?

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3 Answers

  1. Best Answer


    Kris Kortokrax on Oct 24, 2016

    If we try to think about this logically, we need to ask ourselves “If there is no DME associated with an IAP, how could the distances be given relative to DME?

    The only other way to state the distances would be the actual distance between two fixes, each of which should be able to be defined by a latitude/longitude.

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  2. Drew on Oct 25, 2016

    That makes sense. I thought the IFR system would use the lowest common denominator for aircraft capability and make all distances DME. But then again, I guess DME slant range would be negligible most of the time.

    A completely trivial question: would it be safe to assume the DME on airways are based on when the aircraft is flying the MEA?

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  3. Skyfox on Nov 02, 2016

    According to the Aeronautical Chart User’s Guide, all mileages are in NM. My guess would be that since the chart editor doesn’t know what altitude an aircraft is flying and so can’t predict how slant range will affect the DME reading, all distances are shown as actual nautical miles (rounded to the nearest whole mile) rather than a DME reading.

    I mention that it’s rounded to the nearest whole mile because on some airways, you’ll find that the total mileage shown inside the D-arrow symbols and/or at the changeover points won’t equal the sum of the smaller segment lengths leading up to that point.

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