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For 14 CFR 119 certificate holders, Alternate Airport IFR Weather Minimums are prescribed by Operations Specification (Ops Spec) C055, specifically Table 1 of that specification.

Below is a generic example of Table 1:

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The wording in this table is understandable in the context of a traditional, ground-based navigational facilities such as NDB, VOR, or ILS providing an approach. For a simple example, if an airport has an operational VOR navigational facility providing an approach, that satisfies the requirements of the first row with the result that the 400 ft ceiling and 1 sm visibility minimums might apply.

However, some §119 certificate holders are authorized to conduct GPS approaches and to use GPS approaches in determining alternate airport weather minimums. For these operators, the table needs further clarification as it does not provide a framework to derive alternate airport weather minimums based on the GPS approaches that are otherwise authorized to be used for that purpose.

No such clarification seems to be given anywhere else in C055 or elsewhere in the Ops Specs.

How do GPS approaches fit into table 1? Does the Global Positioning System (GPS) constitute a navigational "facility" for the purposes of Table 1? If so, does it constitute a single navigational facility, thereby satisfying the requirements of the first row, just as if a single VOR provided an instrument approach?

Is there guidance provided elsewhere on this?

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Yes, a GPS approach can satisfy the criteria of a navigational facility for the purposes of Table 1 in Ops Spec C055.

The FAA gives the following guidance in Notice 8900.218, Alternate Airport IFR Weather Minimums:

G. 5) Planning for use of GPS-based IAP must be based on a single navigational facility when determining the approach facility configuration in Table 1, even if there are two or more RNAV (GPS) approaches to different suitable runways.

This guidance doesn't go to the length of explicitly including GPS in the definition of "navigational facility". However, it does mean that GPS-based IAP can be understood to substitute for a single navigational facility, thereby satisfying the criteria of the first row of Table 1.

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