schleprock,
there are 3 areas of requirements to be covered before one can execute a cat III approach.
1. Aircraft capabilities - Certified, Fail-Operational/Fail-Passive Automatic Landing System.
2. Crew Training & Certification - Training program, type experience, recurrent training and checking.
3. Airfield - ILS facility, ILS maintenance, approach & runway lighting, runway markings, secondary power supply, ATC procedures, etc.
generally, 3 major bodies governs the different limits and requirements. they are :
ICAO, FAA & JAA
Cat IIIA
ICAO & FAA - No DH or DH < 100 ft (30 m), RVR < 700 ft (200 m)
JAA - DH < 100 ft (30 m), RVR < 700 ft (200 m)
Cat IIIB
ICAO & FAA - No DH or DH < 50 ft (15 m), RVR < 700 ft (200 m) > 150 ft (50 m)
JAA - No DH or DH < 50 ft (15 m), RVR < 700 ft (200 m) > 250 ft (75 m)
Cat IIIC
ICAO & FAA - No DH, No RVR
JAA - Not mention in this sub-category
Hope this helps.
HS