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Chapter 5. Flight controls

Table of Contents

5.1. Elevator faults
5.2. Stabilizer jam
5.3. Aileron faults
5.4. Spoiler faults
5.5. Rudder Jam
5.6. Flaps and/or slats fault/locked
5.7. SFCC faults
5.8. ELAC fault
5.9. SEC fault
5.10. FCDC faults
5.11. Direct Law
5.12. Alternate Law
5.13. Wingtip brake fault
5.14. Flap attach sensor failure
5.15. Flight control servo faults
5.16. Speed brake disagree
5.17. Speed brake fault
5.18. Stiff sidestick/ rudder pedals
5.19. Sidestick unannunciated transducer faults

5.1. Elevator faults

If a single elevator fails, the SECs use the remaining elevator to provide pitch control in alternate law (see Section 5.12, “Alternate Law”). In addition, speed brake should not be used and the autopilots are unserviceable.

If both elevators fail, the only mechanism for pitch control available is manual pitch trim, so pitch reverts to mechanical back up and roll reverts to direct law. For the approach fly a long final, initiating the descent from at least 5000ft AAL. Do not try to flare using trim and do not remove power until after touchdown. From 1000ft AAL, try to keep power changes to within 2% N1. In the event of a go-around, power must be applied very slowly if control is not to be lost.[21]


5.2. Stabilizer jam

Manual pitch trim is a mechanical connection to the stabilizer actuator. It may be possible to use manual pitch trim when the ELACs have detected a stabilizer jam, although it may be heavier than normal. If it is usable, trim for neutral elevators.

The flight controls will revert to Alternate Law. If the stabilizer could not be moved, gear extension should be delayed until CONF 3 and VAPP are achieved so that the elevators are properly trimmed.

If the jam is caused by the mechanical connection, it is possible that the ELACs will not detect the problem. The procedure in this case is similar, but Normal Law will remain.


5.3. Aileron faults

The lateral aircraft handling is not adversely affected even if both ailerons fail, as the systems compensate by using the spoilers. Fuel consumption will, however, increase by approximately 6%.


5.4. Spoiler faults

The effect of a spoiler fault depends on whether the spoiler fails retracted or extended.

If the spoiler fails in the retracted position, handling should not be adversely affected. A CONF 3 landing may reduce any buffeting that is encountered. Speed brake should not be used if spoilers 3 + 4 are affected. The loss of ground spoilers will significantly increase landing distances.

Airbus have identified a failure scenario that leads to high pressure hydraulic fluid reaching the extend chamber of a spoiler actuator via a failed o-ring. This has the effect of a spoiler failing in the fully extended position. In this case, the autopilot does not necessarily have sufficient authority to control the aircraft, and it should be disconnected. Fuel burn will increase significantly; FMGC fuel predictions do not account for the failure and should be disregarded. Green dot speed will minimize this increased fuel burn, but may not be viable if there is excessive buffet – attempt to find a compromise speed. Landing will be flap 3; VAPP and LDG DIST factors are available in QRH IFP.


5.5. Rudder Jam

The main indication of jammed rudder is undue and adverse pedal movement during rolling manoeuvres caused by the yaw damper orders being fed back to the pedals when they are no longer sent to the rudder.

Crosswinds from the side that the rudder is deflected should be avoided, and a cross wind limit of 15kt applies. Control on the ground will require differential braking until the steering handle can be used (below 70kt), so landing distances are increased. Do not use autobrake.


5.6. Flaps and/or slats fault/locked

The most pressing concern following a flap or slat problem is to establish a max operating speed that will avoid overspeeding the device in its locked position. A table is provided on page AEP.F/CTL “Landing with Slats or Flaps Jammed” of the QRH for this purpose, but a quick estimation can be made by establishing what flap lever position would be required to get the device into its current position and using VFE for the configuration associated with that flap lever position as VMO. In doing this, it must be remembered that slat deployment in CONF 2 and CONF 3 is the same (tip: think of available slat positions as being 0, 1, Intermediate or Full). This also affects use of the QRH table; the second dot on the slat indicator on the E/WD should be considered slat 3 for the purpose of this table, not slat 2 as might be expected. The barber’s pole displayed for VFE on the PFD is a function of the flap lever position, so it may be worth initially selecting the flap lever to the matching CONF to have this reference available. For minimum speeds, the VLS displayed on the PFD is calculated from actual flap and slat position and can be trusted.

Unless there is an obvious reason not to (e.g. wing tip brake on, alignment fault or fault due to dual hydraulic failure), the flap lever can be recycled.

If normal operation cannot be restored, there are two major issues that must be quickly addressed. Firstly, fuel burn will be dramatically higher when flying with a locked device. With slats extended, fuel burn will increase by 60%. With flaps extended it will increase by 80%. With slats and flaps extended, fuel burn will double. These figures are available in QRH OPS. The second issue is that landing distances are significantly increased, in the worst case by a factor of 2.2. It may be that the combination of these factors requires a fairly prompt diversion decision.

The flap and slat systems are largely independent, so the flap lever will continue to move the slats if the flaps are locked and vice versa. In general, flap 3 should be selected for landing. There are two exceptions. If flaps are locked at >3, flap full should be used. If both slats and flaps are locked at 0, flap 1 should be used so that the AP/FD go-around is armed. Configurations and VREF increments are available on page IFP.LDwSFSF of the QRH. If a flapless and slatless landing is required, the threshold speed may be below VLS. This is necessary as the landing speeds in this configuration are very close to tyre limit speeds.

During configuration, VLS is computed from actual configuration and VFE next is computed from flap lever position. F and S speeds are essentially meaningless.

The recommended deployment method is to select speed to 5kt below VFE next then select the next configuration as the speed reduces through VFE next.[22] If VLS>VFE next, prioritise VLS: fly VLS, select the next configuration, then track VLS as it reduces with the extension of the lift device. Use of autothrust with selected speed is generally recommended for all phases of the approach, but in this case it will need to be temporarily disconnected until landing configuration is established.

It is worth noting that failure of the slat channels of both SFCCs appears to result in the loss of characteristic speed display on both PFDs. This is not mentioned in the FCOM but occurs in the sim. The upshot of this is that neither VLS nor VSW are available at all, since they are not displayed and there is no way to calculate them. This is of particular concern when trying to configure to flaps 2 since the aircraft must be slowed to VFE(conf 2) when still clean (remember conf 1 is slats only when configuring from conf 0). It is highly likely that the stall warner will activate during the transition, and if not anticipated, the subsequent recovery will overspeed the flaps. The solution is to brief that speed will be reduced very slowly and if the stall warning occurs the speed will be maintained whilst allowing the deployment of the flaps to recover the stall margin.

The autopilot may be used down to 500ft AAL, but since it is not tuned for the abnormal configuration it must be closely monitored.

For the go-around, initially maintain flap/ slat configuration. A speed 10kt lower than max operating speed should be flown. If it is the slats that are jammed or if the flaps are jammed at 0, clean configuration can be used to transit to a diversion airfield.

Other issues include the possible loss of the automatic operation of the center tank pumps (which is sequenced to the slats) and possible reversion to Alternate Law.


5.7. SFCC faults

Each SFCC has fully independent slat and flap channels. A failure of a channel in a single controller will lead to slow operation of the associated surfaces. In addition, the flap channel of SFCC1 provides input to the idle control part of the FADECs and to the EGPWS.

Failure of both flap channels or failure of both slat channels is covered in Section 5.6, “Flaps and/or slats fault/locked”.


5.8. ELAC fault

In normal operations, ELAC 1 controls the ailerons and ELAC 2 controls the elevators and stabiliser. Failure of a single ELAC will result in failover to the remaining computer. Provided no uncommanded manoeuvres occurred, an attempt can be made to reset the failed ELAC.

Failure of both ELACs leads to loss of ailerons and hence Alternate Law. One of the SECs will take over control of the elevators and stabiliser. Again, an attempt can be made to reset the computers.

If the fault is designated a pitch fault, only the pitch function of the associated ELAC is lost.


5.9. SEC fault

Each SEC controls either 1 or 2 spoilers per wing. SEC 1 and 2 also provide back up for the ELACs (see Section 5.8, “ELAC fault”). Loss of a SEC leads to loss of its associated spoilers. SEC 1 provides spoiler position to the FACs. If speedbrakes are deployed with SEC 1 u/s and SEC 3 operative, spoiler 2 will deploy without a corresponding increase in VLS. Therefore, do not use speedbrake if SEC 1 is affected (it won’t do much anyway!).

Pairs of SECs also provide the signal for reverse thrust lever angle to the reversers and spoiler deployment to the autobrake. A dual SEC failure will therefore lead to a loss of a reverser and loss of autobraking.

If all SECs are lost, all the above holds true. Furthermore the flight controls revert to Alternate Law due to the complete loss of spoilers. Also, due to routing of LGCIU data to the ELACs via the SECs, Direct Law will occur at slat extension rather than gear extension.

An attempt should be made to reset the affected SEC(s).


5.10. FCDC faults

The two FCDCs are redundant, so a single failure has no immediate effect.

If both FCDCs fail, the ELACs and SECs can no longer supply data to the EIS. The major effect of this is that F/CTL ECAM warnings are no longer generated. The warning lights on the overhead panel continue to give valid information and should be monitored. The aircraft remains in normal law with all protections, but protection indications (bank and pitch limits, Vα‑prot and Vα‑max) are not shown and the stall warning system becomes active.


5.11. Direct Law

In Direct Law, deflection of the control surfaces is a linear function of deflection of the side-stick and trimming must be done manually. The controls are very sensitive at high speeds. Use of manual thrust is recommended as power changes will result in pitch changes. Similarly, use of the speed brake will result in nose up pitch changes so it should be used with care. Protections are unavailable, so speed is limited to 320kt/0.77M and care must be taken in GPWS or windshear manoeuvres.

Direct Law landings are Config 3; landing distances, in the absence of other pertinent failures, are comparable to normal Config 3 landings.

The major handling difficulty in direct law is the go-around. There is no compensation for the large pitch moment introduced by selecting TOGA power on the under-slung engines, the thrust levers are non-linear and the use of the manual pitch trim wheel will be unfamiliar. Apply power smoothly and progressively and anticipate a requirement for unusual side-stick inputs.

Direct Law works with or without yaw dampers. The aircraft is always convergent in dutch roll, so use lateral control, not rudder, if dutch roll is experienced.


5.12. Alternate Law

In alternate law, pitch is as in normal law, but roll is as in direct law. Load factor protection is retained, but other protections are either replaced with static stability or are lost, depending on the nature of the failure. Stall warnings and overspeed warnings become active.

The main effects are that speed is limited to 320kt and stall warnings must be respected when carrying out EGPWS manoeuvres.

The autopilot may be available.

Expect Direct Law after landing gear extension (see Section 5.11, “Direct Law”), and hence increased approach speeds and landing distances due to a CONF 3 landing (see QRH IFP.LDwFCSF).


5.13. Wingtip brake fault

The wingtip brakes activate in case of asymmetry, mechanism overspeed, symmetrical runaway or uncommanded movements. This protection is lost.


5.14. Flap attach sensor failure

The flap attach sensor detects excessive differential movement between the inner and outer flaps which would indicate failure of a flap attachment. This protection is lost.


5.15. Flight control servo faults

All flight controls have redundant servos. In the case of an elevator servo fault, a restriction to not use speedbrake above VMO/MMO applies.


5.16. Speed brake disagree

This indicates that the spoiler positions do not correspond with the speedbrake lever position. This may be as a result of automatic retraction (alpha floor activation or speed brakes deployed when full flap selected) or as a result of spoiler malfunction. In both cases retract the speedbrake lever and in the case of spoiler malfunction consider the speedbrakes unserviceable.


5.17. Speed brake fault

This indicates a failure of the speedbrake lever transducers rather than a problem with the spoilers. Ground spoiler activation may be expected on selection of reverse, so providing reversers are used, landing distances should not be affected.


5.18. Stiff sidestick/ rudder pedals

This may affect both sidesticks at the same time, but not the rudder pedals or it may affect the rudder pedals and one sidestick. Control forces will remain moderate and the aircraft remains responsive. Confirm autopilot disengagement and consider transferring control if one of the sidesticks is unaffected.


5.19. Sidestick unannunciated transducer faults

It is possible for a failed sidestick transducer to cause uncommanded control inputs. If no fault is detected, the result is that the aircraft behaves as if that input had actually been made. Generally, the autopilot will disconnect and any attempt to control the aircraft with the failed sidestick will fail. The aircraft should be recovered with the other sidestick using the takeover button. Keeping this button pressed for 40 seconds will lock out the failed sidestick, and the autopilot can then be re-engaged. The autopilot should not be disconnected in the normal manner as pressing the takeover button will re-introduce the failed sidestick and the uncommanded input; use the FCU instead.

[21] This is Boeing advice – Airbus does not provide guidance for the flare or go-around technique when elevators are frozen.

[22] Prior to the June 2017 update, the QRH stated that to prevent overspeeds in case of turbulence, it is acceptable to configure at lower speeds as long as speed remains above VLS. This statement has now been removed, most probably to improve the readability of what was a very longwinded explanatory note.