According to alternate airport rules, what is the additional visibility requirement if there is only one nav source for an approach?

The requirement for additional visibility when there is only one navigation source for an approach is focused on ensuring that pilots have sufficient visual references to execute the approach safely. When an approach is conducted using a single navigation source, the potential for errors increases, and this higher risk necessitates an added layer of caution in the form of increased visibility.

Adding 1 statute mile (SM) to the minimum visibility requirement serves to enhance safety by providing more distance for pilots to visually acquire and identify the runway environment before reaching decision height. This extra margin can be crucial, especially in conditions that are marginal or when the approach is reliant on a single source of navigational information.

Understanding the rationale behind this requirement reinforces the concept of safety in aviation operations, particularly in situations where navigation aids may be limited or potentially unreliable.