Definition
A precision instrument approach (typically an ILS) with a decision height (DH) no lower than 200 feet above the touchdown zone elevation and a runway visual range (RVR) no less than 1,800 feet (or visibility of 1/2 statute mile). At the DH, the pilot must have the required visual references to continue the approach to landing; otherwise, a missed approach is required.
Plain English
The most common type of precision instrument landing. The pilot can fly the approach down to 200 feet above the runway in fairly low visibility. At that point, they must see the runway environment to land — if not, they must go around.
Context Anchor
Seen on instrument approach charts, ILS discussions, and approach briefings when identifying what level of low-visibility approach is authorized.
Derivation
The term 'Category' comes from ICAO's classification system, which sorts precision approaches into categories (I, II, III) based on how low the minimums go. Category I is the highest minimums — the easiest tier — with II and III progressively lower and more demanding in equipment and training.
Why Pilots Care
It sets the legal weather limits for continuing an ILS approach to a landing.
Intuition Check
Do not read Category I as just a general label meaning “basic” or “easy.” In instrument flying, it is a specific class of approach minimums tied to altitude, visibility, aircraft equipment, ground equipment, and pilot authorization.
Example Sentence 1
The ILS into Runway 27 is a Category I approach with a 200-foot decision height and 1/2-mile visibility minimums.
Example Sentence 2
Category I approaches can be flown when visibility is 1,800 feet or better.