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4 Answers

H (High Altitude) VOR Standard Service Volume

Asked by: 15722 views Airspace, FAA Regulations, Instrument Rating

The High Altitude VOR Standard Service Volume in the AIM has three different parts to it. The first one says  “From 1,000 feet AGL up to and including 14,500 feet AGL at radial distances out to 40 NM.” I understand that.

Now the next two confuse me:
“From 14,500 AGL up to and including 60,000 feet at radial distances out to 100 NM”.

And

“From 18,000 feet AGL up to and including 45,000 feet AGL at radial distances out to 130 NM”.

I understand from 14,500 AGL the standard service volume increases from 40 NM to 100 NM and from 18,000 feet AGL it increases to 130 NM.

It’s the 60,000 and 45,000 AGL part that’s confusing me. If I’m at 30,000 feet is the service volume 100 NM or 130 NM? In what situations would I use one or the other? Please put this into one or more scenario(s) so I can understand.

Thank you!

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4 Answers



  1. Wes Beard on Apr 01, 2012

    The 18,000 FT AGL To 45,000 FT AGL the service volume is 130 NM takes precedence over the 100NM service volume.
     
    Something that I don’t think is well understood is what service volume means in reference to navigational facilities.  The service volume is a guarantee from the FAA that adequate reception is available.  It does not mean that navigational reception will be lost once you are outside the service volume.  In fact, most VOR’s and NDB have adequate reception at distances greater than the service volume; it is just that the FAA will not guarantee it.
     
    There is always exceptions to the rule.  If a navigational facility cannot guarantee reception in the service volume either due to mountais or other phenomenon the FAA will issue a statement in the airport facilities directory with a statement VOR unusuable from 030 to 060 beyond 30NM.
     
    If the FAA guarantees signal outside the service volume, you will typically find them on the longer airways.  For example, V105 from TUS to GBN is 103NM.  At the MEA, the FAA guarantees acceptable navigational reception. 

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  2. Bill Trussell on Apr 02, 2012

    The issue that is not made clear is one of frequency reuse on the navigation facilities.  At the altitudes below 45,000 feet the engineering is done to ensure proper services are available at the 130NM distances, on a non-interfering basis.  At the higher altitudes they can not guarantee that interference is not possible given two facilities on the same frequency within 260NM of each other, within line of sight of an aircraft at the upper altitudes.  To overcome this issue they “offically” cut down the service volume, in which non-interfering services are guaranteed.
    To answer the question directly now, for flight at 30,000 ft the distance would be 130NM, above 45,000ft it would be cut down to a distance of 100NM to account for possible frequency interference from reuse between two navaids on the same frequency.
     
     

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  3. Andrew K on Apr 04, 2012

    Frequency reuse is probably the most logical reason.
    The only other possibility I can think of is the antenna gain of the VOR facility is not as good at the elevation angle generated by being more than 45,000ft agl and ~100nm away. Do a google on “antenna elevation gain”, the lobes that jut out indicate maximum gain (performance) at a particular angle, vice versa the pits between the lobes are where the antenna has terrible gain.
    This is an educated guess though…

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  4. Bill Trussell on Apr 04, 2012

    I happen to have some aviation spectrum management experience and can tell you with certainty that the sevice volume issue above is driven my reuse requirements.  This may go away or diminish as the FAA moves to minimizing the number of VOR locations in use with inclreases in GPS usage.

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