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4 Answers

Alternate minimums

Asked by: 568 views Instrument Rating

Started instrument training, and read in the alternate minimums, obviously for precision approach it’s 600 ceiling and 2sm. And for non precision approach 800 ceiling and 2sm.

but in the alternate minimums at the international airport near me, it’s says

ILS or LOC 13R  further down says ILS, 700 and 2sm

i can’t find out why an where, please help

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4 Answers



  1. Mark Kolber on Dec 22, 2017

    It would help to provide the name and ID of the airport so we can see exactly what you are talking about.

    Generally, if in the alternate minimums for an airport it says the minimum for the ILS is 700, it means one of a number of conditions exist when disqualify the approach from using the standard alternate minimums, so it gets special ones. In some cases it might even say the approach or airport doesn’t qualify for use as a filing alternate at all.

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  2. John D Collins on Dec 22, 2017

    I agree with Mark, it makes discussing the details much more useful when you identify the airport and the approach.

    The way the alternate minimums are determined is based on the higher of 600-2 or 800-2 respectively for precision non-precision approaches and the minimums for the non precision option. So in your case, 600-2 is probably not higher than the localizer only option of 700-2, so 700-2 is chosen as the non standard alternate minimums. The basic idea is that under worse case conditions, the approach can be still be depended on to be flown to minimums and complete the procedure without the GS and any other ground system failure. In the vast majority of cases, 600-2 is above the localizer option, so it is used by default. When you select an alternate, you want it to be reliably able to be used to land. Since most ILS category 1 procedures have a DH of 200 AGL, a 600 foot alternate criteria provides 400 feet of ceiling buffer with a working GS and protects against the failure of the GS.

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  3. Cody on Dec 22, 2017

    Sorry guys I’m new here I forgot to put where it was, it is at San Antonio International (KSAT)

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  4. John D Collins on Dec 22, 2017

    KSAT ILS RWY 13R has the localizer option with out being able to identify JUPAG with a MDH of 631 feet. So 700 feet is the next higher 100 foot increment that would still allow the procedure to be flown to a successful conclusion with the GS, IANT DME, and the approach lights all out of service.

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