Alternate Selection & the 1-2-3 Rule
Key regulatory and practical concepts for choosing IFR alternates under 14 CFR 91.169 and 91.167.
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Questions Covered in This Set
10 cards to master
State the 1-2-3 rule.
File an alternate unless, from 1 hour before to 1 hour after ETA, the destination forecast shows a ceiling of at least 2,000 ft AGL and visibility of at least 3 SM.
Is the 1-2-3 rule based on current or forecast conditions?
Forecast (TAF). A good METAR right now doesn't matter if the forecast window dips below 2,000/3.
Do TEMPO and PROB groups count for the 1-2-3 rule?
Yes — for planning purposes conditional groups are the forecast; a TEMPO BKN015 in the window forces an alternate.
When is an alternate always required regardless of weather?
When the destination has no instrument approach procedure at all.
Alternate planning minima with a precision approach (ILS/LPV)?
600 ft ceiling and 2 SM visibility at your ETA at the alternate.
Alternate planning minima with only a non-precision approach?
800 ft ceiling and 2 SM visibility at your ETA at the alternate.
Alternate requirement if the airport has no IAP?
Forecast ceiling and visibility must allow descent from the MEA, approach, and landing under VFR.
What do the 600-2 / 800-2 numbers actually limit?
Only the planning decision. Once you divert you fly the approach to its published minimums.
IFR fuel requirement (91.167)?
Enough to fly to the destination, then to the alternate, plus 45 minutes at normal cruise.
Why can a legal alternate still be a bad alternate?
If it shares the same airmass, frontal deck, freezing level, or fog trend, it will likely go down too — seek dissimilar weather, favorable trends, and available services.
