Definition
A precision instrument approach and landing classification permitting operations to a decision height lower than 100 feet (or with no decision height) and a runway visual range not less than 700 feet (200 meters). CAT IIIa requires specialized airborne equipment, a qualified flight crew, an approved operator, and a runway with the necessary ground equipment and lighting.
Plain English
A type of approach that lets a properly equipped aircraft and crew land in very low visibility — down to about 700 feet of forward visibility along the runway — using highly accurate instruments to guide the landing.
Context Anchor
Seen in instrument approach procedures, approach briefings, and operations specifications for very low-visibility landings.
Derivation
‘Category’ comes from Greek katēgoria, meaning ‘a class or division.’ ICAO and the FAA use ‘Categories’ to rank precision approaches by how low the visibility and decision height can be. III is the lowest visibility tier, and ‘a’ is its least demanding sub-level — IIIb and IIIc allow even lower minimums.
Why Pilots Care
Enables safe landings in conditions where standard approaches would not be possible, reducing diversions and improving schedule reliability.
Intuition Check
CAT IIIa does not mean a type of aircraft or a normal instrument approach. It means a specific low-visibility landing category with strict approval and visibility requirements.
Example Sentence 1
With the fog rolling in, the captain confirmed the aircraft and crew were current for CAT IIIa before briefing the approach.
Example Sentence 2
During recurrent training the pilot practiced CAT IIIa procedures to maintain currency for operations in poor weather.