Alternate minimums same as forecast weather
This issue is raised in AIM 5.1.9(b) anyway:
b. The FAA has identified three possible situations where the failure
to plan for an alternate airport when flying IFR to such a destination
airport could result in a critical situation if the weather is less
than forecast and sufficient fuel is not available to proceed to a
suitable airport.
1. An IFR flight to an airport where the Minimum Descent Altitudes
(MDAs) or landing visibility minimums for all instrument approaches are
higher than the forecast weather minimums specified in 14 CFR Section
91.167(b). For example, there are 3 high altitude airports in the U.S.
with approved instrument approach procedures where all of the MDAs are
greater than 2,000 feet and/or the landing visibility minimums are
greater than 3 miles (Bishop, California; South Lake Tahoe, California;
and Aspen-Pitkin Co./Sardy Field, Colorado). In the case of these
airports, it is possible for a pilot to elect, on the basis of
forecasts, not to carry sufficient fuel to get to an alternate when the
ceiling and/or visibility is actually lower than that necessary to
complete the approach.
2. A small number of other airports in mountainous terrain have MDAs
which are slightly (100 to 300 feet) below 2,000 feet AGL. In
situations where there is an option as to whether to plan for an
alternate, pilots should bear in mind that just a slight worsening of
the weather conditions from those forecast could place the airport
below the published IFR landing minimums.
3. An IFR flight to an airport which requires special equipment; i.e.,
DME, glide slope, etc., in order to make the available approaches to
the lowest minimums. Pilots should be aware that all other minimums on
the approach charts may require weather conditions better than those
specified in 14 CFR Section 91.167(b). An inflight equipment
malfunction could result in the inability to comply with the published
approach procedures or, again, in the position of having the airport
below the published IFR landing minimums for all remaining instrument
approach alternatives.
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