Under what weather conditions is an alternate airport required?

An alternate airport is required when the weather conditions at the destination airport are below specified minimums, which, in this case, is when the ceiling is below 2,000 feet and visibility is less than 3 statute miles. This requirement is in place to ensure that pilots have a safe option for landing should they be unable to land at their intended destination due to poor visibility or low cloud ceilings.

The justification for this choice is rooted in safety regulations and flight operation procedures that emphasize the importance of having a clear plan for alternate landing options in adverse weather conditions. If the weather falls below these minimums, there is a significant risk of encountering adverse conditions upon approach, making it essential for pilots to have a designated alternate airport where the weather meets acceptable standards for landing. This practice helps mitigate the risks associated with low visibility and low ceilings during flight operations.