getting to grips with CAT II CAT III operations(5)

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2.2  CATEGORY III
A CAT III operation is a precision approach at lower than CAT II minima.
CAT Ill is divided in three sub-categories: CAT III A, CAT III B, and CAT III C, associated with three minima levels ( CAT III A is associated with highest minima, and CAT III C with lowest minima).
2.2.1  CAT III A DEFINITIONS
ICAO and FAA definition
A category III A approach is a precision instrument approach and landing with no decision height or a decision height lower than 100ft (30m) and a runway visual range not less than 700ft (200m).
JAA definition
A category III A approach is a precision instrument approach and landing with a decision height lower than 100ft (30m) and a runway visual range not less than 700ft (200m).
It is worth noting that the JAA considers that CAT III A is always associated with a decision height (difference with ICAO/FAA).
2.2.2  CAT III B DEFINITIONS
ICAO and FAA definition
A category III B approach is a precision approach and landing with no decision height or a decision height lower than 50ft (15m) and a runway visual range less than 700ft (200m), but not less than 150ft (50m).
JAA definition
A category III B approach is a precision approach and landing with no decision height or a decision height lower than 50ft (15m) and a runway visual range less than 700ft (200m), but not less than 250ft (75m).
Notes:  ICAO/FAA and JAA differ by the minimum RVR associated with CAT III B approaches (50m / 75m).
JAA: Where the DH and the RVR do not fall in the same Category, the RVR will determine in which Category (CAT III A or B) the operation is to be considered.
2.2.3 CAT III C DEFINITION
ICAO and FAA definition
A category III C approach is a precision approach and landing with no decision height and no runway visual range limitation.
CAT III C operations are not currently authorized and the JAA does not mention this sub-category.
Note from ICAO document:
Where the DH and RVR do not fall within the same Category, either the DH or the RVR may determine in which Category the operation is to be considered. The operation will be in the Category with the lower minima.
2.2.4 CAT III OBJECTIVE
The main objective of CAT Ill operations is to provide a level of safety equivalent to other operations but in the most adverse weather conditions and associated visibility.
In contrast to other operations, CAT III weather minima do not provide sufficient visual references to allow a manual landing to be made. The minima only permit the pilot to decide if the aircraft will land in the touchdown zone (basically CAT III A) and to ensure safety during rollout (basically CAT III B).
Therefore an automatic landing system is mandatory to perform Category III operations. Its reliability must be sufficient to control the aircraft to touchdown in CAT III A operations and through rollout to a safe taxi speed in CAT III B (and CAT III C when authorized).
　
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