What does the "1-2-3 rule" pertain to in aviation?

The "1-2-3 rule" in aviation refers specifically to alternate airport requirements during flight planning. This guideline helps pilots determine when they must select and be prepared to divert to an alternate airport based on specific criteria related to weather and visibility.

According to this rule, if the weather at the destination airport is forecasted to be below certain minimums (such as one hour before departure, during the approach, and for the altitude), the pilot must choose an alternate airport. This ensures that there is a safe backup in case conditions at the destination deteriorate. The "1-2-3 rule" thus emphasizes the importance of having a comprehensive plan for safe operations under adverse conditions, enhancing overall flight safety and operational readiness.

In contrast, flight clock management, fuel management, and flight safety protocols address different aspects of flight operations and do not directly relate to the specific requirements for alternate airports that the "1-2-3 rule" outlines.