Classification of ILS approaches by minimum decision height and visibility, from CAT I to CAT III, which allows aircraft to land in dense fog.
What it is
In Category I, the most common, the decision height, at which the crew must have the required visual references in sight to continue, is no lower than 200 feet (60 metres), with a minimum visibility of 800 metres or a runway visual range of 550 metres. Category II allows a descent to 100 feet (30 metres) with a runway visual range of at least 300 metres. Category III permits lower decision heights, or none, with visual ranges below 300 metres. ICAO used to subdivide it into IIIA (from 175 metres), IIIB (from 50 metres) and IIIC; it now treats it as a single category, although the subdivisions remain in common use. ICAO also classes approaches with a decision height below 250 feet as Type B, which are the ones split into these three categories, and the rest as Type A.
Categories II and III demand far more than an antenna: centreline and touchdown zone lighting, protected areas around the antennas, back-up equipment, a suitably certified aircraft, usually with autoland, and specially trained crews. They are therefore found mainly at airports where fog is common or traffic justifies the investment. When low-visibility procedures are in force, spacing between aircraft increases and airport capacity falls.
Related terms
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This page was last updated on October 9, 2026
APA
Vuelopedia. (2026, October 9). ILS categories. Retrieved October 17, 2026, from https://vuelopedia.org/en/glossary/ils-categories
MLA
“ILS categories.” Vuelopedia, Fundación Poderia, 9 Oct. 2026, vuelopedia.org/en/glossary/ils-categories. Accessed 17 Oct. 2026.
Chicago
Vuelopedia. “ILS categories.” Fundación Poderia. Last modified October 9, 2026. https://vuelopedia.org/en/glossary/ils-categories.
Harvard
Vuelopedia (2026) ILS categories. Available at: https://vuelopedia.org/en/glossary/ils-categories (Accessed: 17 October 2026).
BibTeX
@misc{vuelopedia_en_glossary_ils_categories,
author = {{Vuelopedia}},
title = {{ILS categories}},
publisher = {Fundación Poderia},
year = {2026},
date = {2026-10-09},
url = {https://vuelopedia.org/en/glossary/ils-categories},
howpublished = {\url{https://vuelopedia.org/en/glossary/ils-categories}},
urldate = {2026-10-17},
note = {Accessed 2026-10-17}
}Wikipedia
{{cite web |url=https://vuelopedia.org/en/glossary/ils-categories |title=ILS categories |website=Vuelopedia |publisher=Fundación Poderia |date=2026-10-09 |access-date=2026-10-17 |language=en}}