Plain English Meaning

ILS approaches are sorted into levels based on how low the clouds and how poor the visibility can be before the pilot must see the runway. Lower minimums mean a higher category, and higher categories require better equipment on the aircraft, better equipment on the ground, and special pilot training and approval.

Full Definition

A classification system for Instrument Landing System (ILS) approaches based on the lowest decision height (DH) and runway visual range (RVR) authorized for the approach. The categories are , , and (subdivided into , , and ). Each successive category permits operations to lower minimums but requires progressively more capable , more precise , additional training and authorization, and stricter requirements.