Definition
A precision instrument approach and landing classification authorizing operations with a runway visual range below 700 feet and, depending on the subcategory (IIIa, IIIb, or IIIc), a decision height below 100 feet or no decision height at all. Category III operations require specially certified aircraft, qualified flight crews, approved airborne equipment (typically autoland), and a ground installation meeting Category III ILS standards.
Plain English
The lowest-visibility category of instrument landing, used when the runway is barely visible or not visible at all. The aircraft, the crew, and the airport all have to be specially approved, and the airplane usually lands itself using autopilot.
Context Anchor
Seen in instrument approach procedures, airline operating rules, airport low-visibility procedures, and discussions of ILS autoland capability.
Derivation
Category means a class or group. III is the Roman numeral for three. In this phrase, Category III means the third and lowest-visibility class of approved instrument landing operation.
Why Pilots Care
They allow continued safe operations at busy airports when fog or low ceilings would otherwise close the field.
Grounding Statement
Picture an approach where the airplane is guided almost all the way to touchdown before the pilot can clearly see the runway environment.
Intuition Check
Category III does not mean a type of aircraft or a level of pilot certificate. Here it means a specific low-visibility class of instrument approach and landing operation.
Example Sentence 1
The crew briefed a Category III approach into Heathrow because fog had reduced visibility to 300 feet RVR.
Example Sentence 2
The aircraft needed special autopilot certification before it could be used for Category III operations.