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?
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1You may narrow your question as a simple search on wikipedia gives lots of information and great references to answer a significant part of your question. – Manu H Jul 10 '15 at 14:06
4 Answers
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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.
FAA Reference Material
The below links are to comprehensive FAA publications covering the areas as titled.
Thanks @Sports Racer for the comment with links to these documents.
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1Also see FAA AC120-29 for CAT I/II http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC120-29A.pdf and FAA AC120-28 for CAT III http://www.faa.gov/documentLibrary/media/Advisory_Circular/120.28C.pdf – Sports Racer Sep 29 '15 at 21:12
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1It might not hurt to move them into your answer. Sometimes things in comments get lost. – Sports Racer Sep 30 '15 at 13:14
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1It may be worth to note than in Europe CATIIIb is 75m-200m RVR, and DH <100ft. CATIIIa is the same as FAA in Europe. EU-OPS-1 page 81, Aerodrome operating minima, (g) Precision approach — Category III operations – yankee Apr 04 '17 at 07:41
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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.
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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:
- 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;
- 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;
- 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;
- 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;
- 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
MATCS
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- 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')
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A Cat IIIA approach can have a 50' DH for operators that need one. Not sure how wide or narrow that set of operators is, though. – Ralph J May 09 '15 at 17:15
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3Also please note that specifications differ here between FAA and ICAO. These figures are FAA-figures (which may very will be what the OP wanted) – Waked May 11 '15 at 08:18
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1There's also the Alert Height, Read more in FAA AC120-28. http://www.faa.gov/documentLibrary/media/Advisory_Circular/120.28C.pdf – Sports Racer Sep 29 '15 at 21:08