getting to grips with CAT II CAT III operations(38)

*one variable is held at its most adverse value
4.3.3 ROLL-OUT PERFORMANCE
Automatic roll-out is only necessary for specific CAT III operations. The requirement is detailed in JAR-AWO 338: Automatic ground roll control.
The automatic roll-out performance is demonstrated with the same method as touchdown performance, but is measured only by one parameter, i.e, maximum lateral deviation of the aircraft center from the runway center line.
.  When automatic ground roll control or head-up ground roll guidance is being used, the probability that the aircraft will deviate more than 8.2m (27ft) from the runway centerline is less than 5%.
.  Additionally, when the operation is predicated on the provision of fail-operational ground roll control, the probability must be less than 10-6 that the outboard landing gear will deviate to a point more than 21.3m (70 ft) from the runway centerline while the speed is greater than 40 knots.
4.3.4 AUTOMATIC LANDING DISTANCE
The landing distances using auto-land have been established for the aircraft type. When they exceed the comparable values for the required manual landing distances (actual distance x 1.67), they are shown in the approved flight manual (see JAR-AWO 142).
Calculation of the automatic landing distance
The required automatic landing distance is the distance of the airborne phase plus the distance of the ground phase (see figure 4.1), multiplied by the factor 1.15.
D = (Da + Dg) x 1.15
Da is the distance of the airborne phase.
Dg is the distance of the ground phase.

Figure 4.1

Airborne phase
The distance of the airborne phase is the distance from the runway threshold up to the glide slope origin (noted d1 in figure 4.2) plus the mean distance from the glide slope origin up to the touchdown (noted d2 in Figure 4.2), plus the 3x standard deviation of the distance form the glide slope origin to the touchdown (σ d2).
D = d1 + d2 + 3 x σ d2
Figure 4.2

The mean distance from glide slope origin to the touchdown (d2) and the multiples of standard deviation of this distance (σd2) have been established through the results of more than one thousand simulated automatic landings.
Ground phase
The distance of the ground phase for an automatic landing is established using the same method as for a manual landing, assuming a touchdown speed equal to the mean touchdown speed plus the 3x standard deviation of this speed (based on more than one thousand simulated automatic landings).
4.3.5  CONFIGURATIONS AND CONDITIONS TO BE CONSIDERED
The compliance demonstration for the automatic landing system must take into account all essential variables influencing the performance (see JAR-AWO 131 (a) and 132).
A typical example for the set of variables for Airbus aircraft is:
. slat/flap setting,
. aircraft weight and center of gravity,
. engine status (e.g. one engine inoperative),
　
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