A CAT III operation is a precision approach at lower than CAT II minima.
- A category III A approach is a precision instrument approach and landing with no decision height or a decision height lower than 100ft (30m) and a runway visual range not less than 700ft (200m).
- A category III B approach is a precision approach and landing with no decision height or a decision height lower than 50ft (15m) and a runway visual range less than 700ft (200m), but not less than 150ft (50m).
- A category III C approach is a precision approach and landing with no decision height and no runway visual range limitation.
https://www.faa.gov/documentLibrary/.../AC120-29A.pdf
https://www.faa.gov/documentLibrary/...ar/120.28C.pdf