Final answer:
The criteria of a Cat IIIa ILS includes a decision height of as low as 50 feet and a minimum required runway visual range of 700 feet, catering for landings in low visibility with advanced autopilot landing systems.
Step-by-step explanation:
Criteria of a Cat IIIa ILS The criteria of a Cat IIIa Instrument Landing System (ILS) encompasses specific minimums regarding visibility and decision height for aircraft landings. A Cat IIIa ILS allows for a decision height as low as 50 feet (15 meters), which is the height at which a pilot must make the decision to continue the landing or execute a missed approach. Furthermore, this category requires a runway visual range (RVR) of no less than 700 feet (200 meters). Advanced autopilot systems are typically used to perform landings under these conditions, allowing for landings in extremely low visibility situations. The system is designed to provide guidance for both the lateral (azimuth) and vertical (elevation) plane. It's worth noting that the equipment onboard the aircraft, as well as ground facilities, must be appropriately certified to meet the stringent requirements of a Cat IIIa ILS.