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REQUIREMENTS FOR FILING A:
TAKEOFF ALTERNATE (TALT/)
If wx at the ORIGIN AIRPORT are below the landing mins, you must specify an alternate airport within: 1 hour from the departure airport with one engine inoperative1)
ENROUTE ALTERNATE (RALT/)
LANDING ALTERNATE (ALTN/)
You must file an alternate if: for at least 1 hour before and for 1 hour after the estimated time of arrival at your destination, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles (1-2-3 rule)
Your alternate must:
For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:
- Precision Approach: Ceiling 600 feet and visibility 2 statute miles.
- Nonprecision Approach: Ceiling 800 feet and visibility 2 statute miles.
For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown
If no instrument approach procedure has been published and no special instrument approach procedure has been issued by the Administrator to Hartlantair, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.
References: https://flighttrainingcentral.com/2025/02/how-to-choose-the-best-alternate-airport-for-your-ifr-flight-a-pilots-guide/ https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-91/subpart-B/subject-group-ECFRef6e8c57f580cfd/section-91.169