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1.3 ECONOMIC ASPECTS
CAT II / CAT III equipment represent a significant cost for an airline. However, it is the only way to keep in-line services during the whole year without any diversion. Weather conditions mainly depend on the airfield location, nevertheless actual CAT II or CAT III conditions may occur at any airfield during some periods of the year. Diversions are expensive for an airline: directly by passenger compensation costs but also by the resulting bad "image". For these reasons, getting operational approval for CAT II and CAT III approaches may be considered as a necessary step in the evolution of a modern airline.

CHAPTER 2
2. GENERAL CONCEPTS
2.1 CATEGORY II
2.2 CATEGORY III
2.3 DECISION HEIGHT AND ALERT HEIGHT
2.4 RUNWAY VISUAL RANGE
2.5 FAIL-PASSIVE AUTOLAND SYSTEM
2.6 FAIL-OPERATIONAL AUTOLAND SYSTEM
2.7 MINIMUM APPROACH BREAK-OFF HEIGHT
2.8 CONCEPT OF MINIMA
This chapter addresses some essential definitions and concepts for CAT II or III operations. The definitions are taken from ICAO, FAA, or JAA documents and are presented in a separate way when necessary.
2.1 CATEGORY II
2.1.1 CAT II DEFINITIONS
The category II is a precision approach corresponding to weather minima as mentioned here below:
ICAO definition
A category II approach is a precision instrument approach and landing with decision height lower than 60m (200ft) but not less than 30m (100ft), and a runway visual range not less than 350m (1200ft).
FAA definition
A category II approach is a precision instrument approach and landing with decision height lower than 200ft (60m) but not lower than 100ft (30m), and a runway visual range less than 2400ft (800m) but not less than 1200ft (350m).
JAA definition
A category II approach is a precision instrument approach and landing with decision height lower than 200ft (60m) but not lower than 100ft (30m), and a runway visual range not less than 300m (1000ft).
The three definitions refer to the concepts of Decision Height (DH) and Runway Visual Range (RVR), which will be explained later in this chapter. It is worth noting the difference between Cat II definitions by ICAO and FAA, and the definition by JAA of the minimum runway visual range (not less than 350m for ICAO and FAA but not less 300m for JAA).
2.1.2 CAT II OBJECTIVE
The main objective of CAT II operations is to provide a level of safety equivalent to other operations, but in more adverse weather conditions and lower visibility.
The desired level of safety is achieved through:
. Airborne equipment,
. Non-visual aids (ILS facility),
. Visual aids (runway marks, lighting systems),
. Flight crew training,
. Flight crew procedures,
. ATC procedures,
. Aircraft maintenance,
. Airfield maintenance,
. Criteria for obstacle clearance.

CAT II weather minima has been established to provide sufficient visual references at DH to permit a manual landing (or a missed approach) to be executed (it does not mean that the landing must be made manually).
　
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