Definition
A precision instrument approach and landing classification permitting operations to runway visual ranges (RVR) below those allowed in Category II. CAT III is subdivided into CAT IIIa, IIIb, and IIIc, with progressively lower or no decision height (DH) and progressively lower RVR minimums, down to zero visibility in CAT IIIc. CAT III approaches require specially certified airborne equipment (typically autoland or a fail-operational/fail-passive autopilot system), a qualified flight crew, and a CAT III–certified ILS facility with the associated ground infrastructure and protected critical areas.
Plain English
CAT III is the lowest-visibility category of ILS approach. The aircraft, the pilots, and the airport ground equipment all have to be specially approved for it, and most CAT III landings are flown by the autopilot all the way to touchdown because the pilot may not be able to see the runway until the wheels are almost on it.
Context Anchor
Seen in instrument approach procedures, ILS minimums, airport low-visibility operations, and aircraft authorization documents.
Derivation
Category comes from the Greek kategoria, meaning 'a class or division.' The ILS categories (I, II, III) divide approaches by how low a pilot is allowed to descend and how poor the visibility can be before the approach must be abandoned. CAT III is the third and most demanding division.
Why Pilots Care
Allows landings in fog or very poor weather that would otherwise force a missed approach or diversion.
Grounding Statement
A CAT III approach is for landing when the runway environment may appear only at the very end of the approach, or not until the landing system has already brought the aircraft to the runway.
Intuition Check
Do not read CAT III as simply “level three” or as an easier category. In ILS operations, CAT III is the most demanding low-visibility category and requires specific approval and equipment.
Example Sentence 1
With the airport reporting RVR 600, only aircraft and crews approved for CAT III could shoot the approach; everyone else diverted.
Example Sentence 2
Only aircraft with the proper certification and crew training may fly to CAT III minimums.