The 1-2-3 Rule: When You Need an IFR Alternate (91.169)
When an IFR flight plan must list an alternate airport, the 1-2-3 rule that exempts you, and the alternate weather minimums and fuel that go with it.
Every IFR flight plan must consider an alternate airport — somewhere to go if you cannot get in at the destination. 14 CFR 91.169 tells you when you must actually file one.
The 1-2-3 rule
You are not required to file an alternate if, for at least one hour before to one hour after your estimated time of arrival, the destination weather forecast shows:
- a ceiling of at least 2,000 feet above the airport elevation, and
- visibility of at least 3 statute miles.
"1-2-3": within 1 hour, 2,000-foot ceiling, 3 miles visibility. If the forecast does not meet *both*, you must file an alternate. (And if the destination has no instrument approach procedure at all, you always need an alternate.)
Alternate weather minimums
An airport qualifies as your alternate only if its forecast at your ETA meets the alternate minimums. When the alternate has a published procedure, use its charted alternate minimums; otherwise the standard minimums are:
- Precision approach: ceiling 600 feet and visibility 2 statute miles.
- Non-precision approach: ceiling 800 feet and visibility 2 statute miles.
If the alternate has no instrument approach, the ceiling and visibility must allow a descent from the MEA, approach and landing under basic VFR.
Don't forget the fuel
Filing an alternate also drives your fuel requirement: 14 CFR 91.167 requires enough fuel to fly to the destination, then to the most distant alternate, and then for 45 minutes at normal cruise. See fuel planning and required reserves.
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*Reference and training only — not for navigation or as legal advice. Always consult the current 14 CFR, the AIM, your aircraft’s POH/AFM and a certificated flight instructor.*