This section covers operational visibility. Operational visibility is important for obvious reasons and is surprisingly not well understood. Many factors affect the visibility minimums depicted on each approach plate for a particular airport. These visibility minimums are depicted as limiting factors but are otherwise advisory in nature. The parameters affecting various approach options are depicted in Figure 1.
Precision approach categories and visibility minimums
Many factors may affect the visibility minimums depicted on a particular approach plate. These include the availability of a precision approach, low visibility, approach lights, and obstacle clearance. Table 1 lists most of the modifying factors.