What is different between a Cat IIIA, Cat IIIB, and Cat IIIC ILS approach?

Question

In terms of aircraft equipment, approach minimums, procedural differences, and anything else relevant, how do the 3 types of a Cat III ILS differ from one another?

Answer 1

ICAO and FAA CAT III definitions

A CAT III operation is a precision approach at lower than CAT II minima. Sub-categories are listed below.

• 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.

*I've omitted the JAA definitions.

Source Airbus Flight Operations Support documentation.

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FAA Reference Material

The below links are to comprehensive FAA publications covering the areas as titled.

FAA AC120-29 for CAT I/II.

FAA AC120-28 for CAT III.

Thanks @Sports Racer for the comment with links to these documents.

Answer 2

From: AC 120-118 https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_120-118.pdf

CAT I (FAA) An instrument approach operation with a minimum descent altitude (MDA), decision altitude (DA), or decision height (DH) not lower than 200 feet (60 m) and with either a visibility not less than ½ SM, or a Runway Visual Range (RVR) not less than 1800 feet (550 m).
CAT I (ICAO) Any precision approach and landing operation with a DA/H of 60 m (200 feet) or higher and with a minimum visibility of 550 m RVR or greater will be termed a Standard CAT I operation.

CAT II (FAA)
A precision instrument approach operation with a DH lower than 150 feet but not lower than 100 feet and a RVR not less than 1000 feet.
CAT II (ICAO)
Standard CAT II operations are made to a DA/H below 60 m (200 feet), but not lower than 30 m (100 feet), with associated RVRs ranging from 550m (1800 feet) to 300 m (1000 feet).

CAT III (FAA)
A precision instrument approach and landing operation with a DH lower than 100 feet (30 m) or no DH, or a RVR less than 1000 feet (300 m).
CAT IIIa (ICAO)
A precision instrument approach and landing operation with a DH lower than 30 m (100 feet) or no DH and an RVR not less than 175 m (600 feet).
CAT IIIb (ICAO)
A precision instrument approach and landing operation with a DH lower than 15m (50 feet) or no DH and an RVR lower than 175m (600 feet) but not less than 50m (200 feet).
CAT IIIc (ICAO)
A precision instrument approach and landing with no RVR limitations.

Answer 3

Most recent European Law (so at least applicable in Europe):

A "type A instrument approach operation” means an instrument approach operation with a minimum descent height or decision height at or above 75 m (250 ft);

A "type B instrument approach operation” means an instrument approach operation with a decision height below 75 m (250 ft). Type B instrument approach operations are categorised as follows:

1. Category I (CAT I): a decision height not lower than 60 m (200 ft) and with either a visibility not less than 800 m or a runway visual range not less than 550 m;
2. Category II (CAT II): a decision height lower than 60 m (200 ft), but not lower than 30 m (100 ft) and a runway visual range not less than 300 m;
3. Category IIIA (CAT IIIA): a decision height lower than 30 m (100 ft) or no decision height and a runway visual range not less than 175 m;
4. Category IIIB (CAT IIIB): a decision height lower than 15 m (50 ft) or no decision height and a runway visual range less than 175 m, but not less than 50 m;
5. Category IIIC (CAT IIIC): no decision height and no runway visual range limitation;’.

https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32018R0401&from=EN

Answer 4

• Cat III A 600 feet (180 meters) Runway Visible Range (RVR)
• CAT III B 150 feet (46 meters) RVR
• CAT III C zero visibility

No decision height in any CAT III approach (CAT II is 100' and CAT I is 200')