What does the 1-2-3 rule specify for filing an alternate airport?

The 1-2-3 rule is a guideline used to determine whether an alternate airport is suitable for landing under IFR (Instrument Flight Rules) conditions. According to this rule, for an alternate airport to be acceptable, the weather must meet specific criteria within a certain time frame around the estimated time of arrival.

The correct specification is indeed that the forecast must indicate a ceiling of at least 2,000 feet and visibility of at least 3 statute miles from 1 hour before to 1 hour after the estimated time of arrival. This ensures that pilots have a reasonable assurance of being able to land at the alternate airport should they need to divert, providing a safety margin that balances both visibility and cloud cover.

The other options do not align with the established parameters set by regulatory standards regarding alternate airports. For instance, the distance from the primary airport is not explicitly capped at 180 miles under this rule, nor does wind speed criteria for alternate airports typically factor into the basic requirements for using an alternate. Lastly, simply having clear weather within a certain number of hours does not encompass all the necessary factors that the 1-2-3 rule covers. Thus, while all options touch on operational considerations, only the first option accurately represents the requirements specified by