Definition
A classification system for Instrument Landing System (ILS) approaches that defines how low a pilot may descend on the approach before needing to see the runway environment, and how much forward visibility is required to land. The categories are: Category I — a precision approach with a decision height not lower than 200 feet above the runway and visibility not less than 1/2 statute mile or runway visual range (RVR) 2400 feet (RVR 1800 feet with touchdown zone and centerline lighting). Category II — a precision approach with a decision height lower than 200 feet but not lower than 100 feet, and RVR not less than 1200 feet. Category IIIA — no decision height or a decision height below 100 feet, and RVR not less than 700 feet. Category IIIB — no decision height or a decision height below 50 feet, and RVR less than 700 feet but not less than 150 feet. Category IIIC — no decision height and no RVR limitation.
Plain English
ILS approaches come in different grades. The higher the category, the lower the cloud ceiling and the worse the visibility you're allowed to fly the approach in. Category I is the basic version most pilots use. Categories II and III let specially trained crews and equipment land in much worse weather, all the way down to essentially zero visibility for Category IIIC.
Context Anchor
Seen on instrument approach charts, in approach minimums, and in discussions of low-visibility landings.
Derivation
Category comes from a word meaning a class or group. In this term, it means the ILS approach is placed into a specific group according to how low the approved weather minimums are.
Why Pilots Care
The category determines whether the aircraft, crew, and airport lighting allow a legal approach in low visibility, directly affecting go/no-go decisions and landing safety.
Grounding Statement
The lower the visibility, the more precise and reliable the whole landing system must be before an ILS approach is allowed to continue close to the runway.
Intuition Check
Do not read “category” as a general difficulty rating. Here, an ILS category is a formal approval level tied to specific landing minimums, equipment, and authorization.
Example Sentence 1
The weather was reporting 300-foot ceilings and 3/4 mile visibility, which was well within Category I ILS minimums for the approach.
Example Sentence 2
After checking the ILS Categories, the crew confirmed the airport supports Category III approaches and briefed the lower minimums accordingly.