What are alternate minimums?

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.



Alternate minimums are specific weather criteria—ceiling and visibility—that must be met at an alternate airport to legally list it on an IFR (Instrument Flight Rules) flight plan. In 2026, standard FAA minimums remain 600-foot ceilings and 2 miles visibility for precision approaches, and 800-foot ceilings and 2 miles visibility for non-precision approaches. Pilots use the "1-2-3 rule" to determine if an alternate is required: if weather at the destination is forecast to be less than a 2,000-foot ceiling or 3 miles visibility within 1 hour before to 1 hour after the ETA, an alternate must be filed. These minimums act as a safety buffer, ensuring that if you cannot land at your primary destination, your backup airport has high enough weather margins to guarantee a safe landing using available instruments.

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14 CFR 91.169 (b) (2) (i) states that an alternate airport is not required if “for at least 1 hour before and for 1 hour after the estimated time of arrival the ceiling will be at least 2000 feet above the airport elevation and the visibility will be at least 3 statute miles.” To help remember those conditions of the ...

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Many pilots refer to this as the 1-2-3 rule: Plus or minus 1 hour from arrival, ceilings at least 2,000 feet and visibility at least 3 statute miles.

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This is the ol' 1-2-3 rule. There are a couple of gotchas. If your destination has no approach, an alternate is always required. Curiously, though, the alternate need not have an instrument approach if the weather allows a descent from MEA under basic VFR, assuming the airport isn't otherwise disqualified.

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That's why pilots are taught the 1 in 60 rule, which states that after 60 miles, a one-degree error in heading will result in straying off course by one mile. Which means the lake you planned to fly over could turn out to be a mountain.

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Not more than one hour from the departure airport at normal cruising speed in still air with one engine inoperative. (2) Aircraft having three or more engines. Not more than two hours from the departure airport at normal cruising speed in still air with one engine inoperative.

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What is the distance for flying aircraft set by the regulations? Commercial aircraft flying below 29,000 feet must maintain a vertical separation of 1,000 feet. Any higher and the separation increases to 2,000 feet, except in airspace where Reduced Vertical Separation Minimum (RVSM) applies.

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In aviation, the rule of three or 3:1 rule of descent is a rule of thumb that 3 nautical miles (5.6 km) of travel should be allowed for every 1,000 feet (300 m) of descent. For example, a descent from flight level 350 would require approximately 35x3=105 nautical miles.

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Larger airports usually have several runways in different directions, so that one can be selected that is most nearly aligned with the wind. Airports with one runway are often constructed to be aligned with the prevailing wind.

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Airports without weather reporting, or approaches with unmonitored approach equipment, can't be used as an alternate.

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As part of the testing of a new aircraft, the manufacturer must demonstrate that all passengers can be evacuated in a short amount of time when an emergency arises - within 90 seconds to be precise. If it doesn't comply, the aviation authorities won't approve its safety certification.

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