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Chapter 11. Auto-flight

Table of Contents

11.1. FAC faults
11.2. Yaw damper faults
11.3. Rudder trim faults
11.4. Rudder travel limiter faults
11.5. FCU faults

11.1. FAC faults

Failure of a single FAC results in loss of redundancy and hence loss of Cat 3 Dual. In particular, a single FAC provides all the characteristic speeds (VSW, VLS, VFE, VFE-next, VLE, VMO/MMO, Green dot, S speed and F speed). It may be worth cross-checking against QRH OPS.OD “Operating Speeds“.

If both FACs are lost the rudder travel limit system, rudder trim control, yaw damper and PFD characteristic speeds are lost and Alternate Law with mechanical yaw control becomes active. Recovery of full rudder authority at flap extension should be anticipated, but use rudder with care above 160kt.


11.2. Yaw damper faults

A single failure leads to loss of redundancy, and hence loss of Cat 3 Dual. On some airframes a reset of the affected FAC can be attempted.

With a dual failure a reset of the FACs should be attempted. If the yaw damper is not recovered, the flight controls revert to alternate law (see Section 5.12, “Alternate Law”). Unless the failure occurred below alert height, only Cat I will be available.


11.3. Rudder trim faults

Loss of a rudder trim from a single FAC leads to loss of redundancy and hence loss of Cat 3 Dual.

If complete loss of rudder trim occurs, an attempt should be made to reset the FACs. If this is not successful, only Cat I is available.


11.4. Rudder travel limiter faults

Loss of rudder limit functionality from a single FAC leads to loss of redundancy only.

The effect of complete loss of rudder limiter functionality depends on when the failure occurred. In general, the rudder should be used with caution when above 160kt. An attempt should be made to recover the limiter by resetting the FACs. If unsuccessful, full rudder travel authority may or may not be recovered at slat extension. If a landing must be made with the rudder travel limiter frozen in the high speed regime, max crosswind is reduced to 15kt and differential braking may be required on the landing roll (do not arm autobrake).


11.5. FCU faults

Loss of a single channel will result in the spare channel automatically taking over. All that is required is a cross check of the baro refs.

Loss of both channels leads to loss of all FCU and EFIS panels. The autopilots, flight directors[37] and autothrust are lost and parameters that are normally controlled by the panels revert to sensible default values. If the weather radar image remains displayed, disregard it since the scale will be incorrect. Since it will only be possible to set the QNH on the standby altimeters, the MDA should not be set in the MCDU; instead the PM should make standard callouts from the standby altimeter.


[37] Flight Directors will pop up to provide guidance in the event of a go-around.