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As I asked question about weather minimums yesterday, I've read some material including TERPs. And In the FAA 8260.3b, 'Taking and Landing Minimims' 3.1 there is one sentence "alternate minimims, when specified, must be stated as ceiling and visibility."
But I don't know What alternate minimums exactly means because I am not native English speaker. I have used English dictionary to find exact meaning but failed.
What is the difference between approach minimums and alternate minimums?
FAR 91.169 states that IFR flight plans must include an alternate airport unless the weather is at least 2000 ft ceiling and 3 miles visibility, from one hour before to one hour afterwards (1-2-3 rule).
The same regulation also states that the alternate airport must meet the following critera:
(c) IFR alternate airport weather minima. Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:
(1) If an instrument approach procedure has been published in part 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima:
(i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:
(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.
(B) For a non-precision approach procedure. Ceiling 800 feet and visibility 2 statute miles.
The difference between APPROACH minimums, and ALTERNATE minimums:
APPROACH minimums are stated on each approach plate, for instance, 200 ft. ceiling with 3 mi. visibility. It's a real-time minimum, because it only affects whether or not you can begin that particular instrument approach. On arrival, you check the airport's weather (METAR, for instance) and if the real weather is reported better than the required weather for a particular approach, then you can begin that approach. Therefore, you need to take the destination weather forecast into account when planning.
ALTERNATE minimums affect your PLAN, even BEFORE you take off, and is not related to approach minimums. An "alternate" refers to a second airport you identify in your planning that you can go to if the weather at the destination turns too bad to land. The thinking is that, if the weather at the destination is FORECASTED to be good around your arrival time (an hour before til an hour after), then you shouldn't need to list an alternate airport in your flight plan. Generally, the destination's weather has to be FORECASTED more than 2,000 ft. ceilings and 3 miles visibility, or if not, you have to IDENTIFY an alternate destination airport in your flight plan. The FORECASTED weather at the ALTERNATE airport has to be better than a certain ceiling / visibility, too. You have to look at the approaches available at the alternate to know what the minimum requirements are there. If the alternate airport has a "precision" approach (for instance, an ILS), the FORECASTED weather at the ALTERNATE has to be at least 600 ft. ceiling and at least 2 mi visibility, otherwise you can't list it as an alternate. But airports with a non-precision approach (for example, a VOR-A approach) require better conditions with 800 ft. ceilings.
I found an excellent article about it at IFR Magazine.
Basically, to qualify as an alternate airport, the alternate must have certain forecast weather conditions (600-2 for precision approach, 800-2 for non-precision.) These are the "alternate minimums".
However, those are just the default values. Many airports have different values, in which case the alternate minimums will be published on the approach plate (example: PAO VOR approach, top-left, next to the inverted 'A')
