getting to grips with CAT II CAT III operations(14)

Figure 3.3 Category II DH

3.2.3 DETERMINATION OF THE DH FOR CATEGORY III
To establish a DH for a particular Category III operation, an operator must take into account only three parameters as explained in this extract of the JAR-OPS.
An operator must ensure that the decision height for a Category III operation is not lower than:
-The minimum decision height specified in the AFM.
-The minimum decision height to which the precision approach aid can be used solely by reference to instruments.
-The decision height to which the flight crew is authorized to operate.
Extract of JAR-OPS
There is no need to take obstacle clearance into account in the determination of the DH. A Category III approach ensures that the aircraft is within the Obstacle Free Zone (see definition of the OFZ in Chapter 5.6) during the approach and go-around.
If the minimum DH is not specified in the AFM, the MABH or the information on the height loss after go around (refer to § 2.7) can be used to determine the minimum DH.
Figure 3.4 Category III DH

3.2.4 DETERMINATION OF RVR FOR CATEGORY II
The table of figure 3.5 provides commonly "acceptable Category II RVR minima" according to ICAO,FAA, and JAA.
The RVR minima according to ICAO are taken from the ICAO document "Manual of All Weather Operations". The RVR minima according to FAA are taken from the AC120.29. The RVR minima according to JAA are taken from the JAR-OPS.
As it is sometimes necessary to increase DH, the RVR minima according to JAA and FAA are a function of the DH.
Figure 3.5 Category Il RVR minima
ICAO 
 FAA  JAA 
DH  RVR  DH  RVR  RVR 
100ft  350m (1200ft)  100-120ft  1200ft (350m)  350m/300m (1) 
121-140ft  1200ft (350m)  400m 
150ft  500m (1600ft) 
 141-180ft  1600ft (500m)  450m 
181-199ft  1800ft (550m)  450m 

Note 1:  300m for aircraft with AP in command down to a height which is not higher than 80% of the applicable DH. 
Note 2:  The RVR minima 350m according to ICAO is called basic CAT II minima and the RVR minima 500m is called restricted CAT II minima. ICAO recommends use of the restricted CAT II minima for the operational evaluation phases prior to authorization of basic CAT II minima. 

3.2.5 DETERMINATION OF RVR FOR CATEGORY III
The table of Figure 3.6 provides commonly "acceptable Category III RVR minima" according to ICAO. This table is taken from "Manual of All Weather Operations".
The table of Figure 3.7 provides commonly "acceptable Category III RVR minima" according to FAA. This table is compiled from information taken from AC120.28C.
The table of Figure 3.8 provides commonly "acceptable Category III RVR minima" according to JAA. This table is taken from the JAR-OPS.
　
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