Control Surface Fault Spectrum

The F/CTL chapter of the ECAM holds several dozen amber cautions. They look like a long, unordered list — but they are not. Behind them is a clean taxonomy: a caution is either a surface or servo losing actuation, or a computer failing, or the control law stepping down, or an input device losing a sensor, or a high-lift problem, or a trim / speedbrake / damping anomaly, or a take-off configuration cross-check reporting a mismatch. Put that taxonomy in your head and any F/CTL ... line you have never seen before can be placed — which family, how serious, which article to open — in a few seconds.

This article is the index to the whole spectrum. The earlier articles each enlarged one block: the surfaces (Ailerons through Ground Spoilers), the computers and law degradation (EFCS Computer Failures), the high-lift failures (High-Lift Failures), the jam and loss-of-control procedures (QRH Jam and Loss of Control). Here we do the reverse: take the complete population of F/CTL cautions from FCOM PRO-ABN-F/CTL, sort each one by its triggering condition, and point it at the article that develops it. It does not re-teach the mechanisms — it is the triage desk you stand at when a caution appears, before you walk to the right specialist.

[!warning]- The alert name alone does not tell you how serious the failure is — the triggering condition does.

Many F/CTL cautions come in a graded family that shares almost the same name. An elevator can raise F/CTL ELEV SERVO FAULT (one servojack lost — mild), F/CTL L(R) ELEV FAULT (both servojacks on one elevator lost — that elevator gone), or F/CTL L+R ELEV FAULT (both elevators lost — pitch on the THS alone). The same is true of the ailerons, and of F/CTL FLAPS FAULT versus F/CTL FLAPS LOCKED. If you read only the headline word "ELEV FAULT" you cannot rank the threat; you must read the degree in the triggering condition — one servo, both servos, or the whole surface; FAULT (channels failed) or LOCKED (wing-tip brake clamped, irreversible). Severity lives in the triggering condition, never in the name.

1. The premise — an index, not a re-teach

A single F/CTL caution asks the crew three quick questions before any procedure begins: what kind of fault is this, how bad is it, and where is the full story? The chapter's deep-dive articles answer the third question one block at a time. This article answers all three at a glance by laying the entire caution list against one organising grid.

Two boundaries keep the article honest:

• It is classification + mapping, not mechanism. Each caution's full ECAM procedure, STATUS limits, and engineering rationale live in the article it maps to. Here you get the triggering condition (verbatim), a one-line effect, and a link.
• The seven-family split is a teaching structure, not a manual chapter. FCOM lists the cautions alphabetically; grouping them into seven families is an organising device for fast triage. The triggering conditions are verbatim manual text; the families are the synthesis on top.

Every caution below is an amber Level-2 (L2) caution in PRO-ABN-F/CTL — none of them is a red Level-3 warning. That is itself worth noting: the F/CTL system is built so deep that even severe surface losses present as cautions, not warnings, because a surviving path almost always remains.

2. The seven families

        F/CTL CAUTION SPECTRUM  (PRO-ABN-F/CTL, sorted by triggering condition)

  (1) SURFACE / SERVO ───────────► a surface loses one or more actuators
      AIL SERVO · L(R) ELEV · RUDDER · SPLR · STAB CTL      → surfaces 18-23
                                                              + 19/32 for pitch
  (2) COMPUTER ──────────────────► PRIM / SEC / FCDC fails
      PRIM · SEC · PITCH FAULT · LAWS REDUND · FCDC          → 01 / 32 / 04
                                                              
  (3) LAW DEGRADATION ───────────► protections drop, limits arrive
      ALTN LAW · DIRECT LAW                                  → 12 / 13 / 32
                                                              
  (4) INPUT DEVICE ──────────────► a sidestick / pedal / sensor fails
      SIDESTICK · RUD PEDAL · SENSOR                         → 16 / 02 / 20
                                                              
  (5) HIGH-LIFT ─────────────────► flap / slat / WTB fault or lock
      FLAPS · SLATS · FLAP SYS · TIP BRK · LEVER             → 25 / 30 / 34
                                                              
  (6) TRIM / SPEEDBRAKE / DAMP ──► trim, speedbrake or damper anomaly
      RUD TRIM · SPD BRK · GND SPLR · TURB DAMP              → 20 / 22 / 23 / 11
                                                              
  (7) T.O CONFIG CROSS-CHECK ────► entered config disagrees with measured
      PITCH TRIM/MCDU/CG · FLAP/MCDU DISAGREE                → 21 / 25 / 30

The triage mnemonic. Read the keyword in the caption: a word like SERVO / ELEV / AIL / RUDDER / SPLR / STAB is family (1) — a surface; PRIM / SEC / FCDC is (2) — a computer; LAW is (3) — a law step-down; SIDESTICK / PEDAL / SENSOR is (4) — an input; FLAP / SLAT / TIP BRK / LEVER is (5) — high-lift; RUD TRIM / SPD BRK / GND SPLR / TURB DAMP is (6) — trim/speedbrake/damping; and DISAGREE (with a MCDU / CG token, and triggered by the TO CONFIG pb or FLEX/TOGA) is (7) — a configuration cross-check. One keyword narrows fifty cautions to a single family and two or three articles.

3. The full spectrum

Each row gives the caution, its verbatim triggering condition (from FCOM PRO-ABN-F/CTL), the operational effect, and the article that develops it. Representative cautions are also quoted in full below their table.

3.1 Surface / servo family

The graded structure is clearest on the elevators. Per FCOM PRO-ABN-F/CTL:

This alert triggers when there is loss of one servojack on one elevator.

This alert triggers when there is loss of both servojacks on one elevator.

This alert triggers when both elevators are lost.

Three distinct cautions, three different severities, from "one servo down on one surface" to "no elevators at all — pitch is the THS now." The same one-then-both gradient governs the ailerons (AIL SERVO FAULT → L(R) INR(OUTR) AIL FAULT). The rudder, being driven by three parallel servocontrols, loses one at a time. Per FCOM PRO-ABN-F/CTL:

This alert triggers when the blue, green, or yellow rudder servojack is lost.

That caution — F/CTL RUD B(Y)(G) SERVO FAULT — is the loss of one of the three; with the other two driving, the rudder is still controllable. It is a different caution entirely from the jam case in the next callout.

[!warning]- F/CTL RUDDER FAULT is the jammed-rudder caution, not a generic "rudder has a fault".

The natural reading of F/CTL RUDDER FAULT is "something is wrong with the rudder." Its actual triggering condition is far more specific. Per FCOM PRO-ABN-F/CTL: This alert triggers when the rudder is detected to be faulty, or jammed, in the 0° position. This is the rudder-jammed-at-neutral case — its STATUS carries MANEUVER WITH CARE, a MAX X WIND FOR LDG: 15 KT limit, and differential-braking guidance for the landing roll. The "lost one servojack but still controllable" case is the other caution, F/CTL RUD B(Y)(G) SERVO FAULT. Do not let the plain name RUDDER FAULT lull you into reading it as a minor servo loss; reach straight for the jam procedure (Rudder and Yaw, QRH Jam and Loss of Control).

And the stabiliser caution names the moment the only mechanical channel takes over. Per FCOM PRO-ABN-F/CTL:

This alert triggers when there is a loss of the electrical control of the stabilizer.

With electrical THS control gone, the crew trims pitch on the manual wheel — the last-resort mechanical path from THS.

3.2 Computer family

The whole point of EFCS Computer Failures is that a single computer fault is not a law degradation: the master role hands over, the survivors cover the failed box (spoilers excepted), and the law stays Normal. The dedicated caution for "running out of Normal-Law spares" makes the distinction explicit. Per FCOM PRO-ABN-F/CTL:

This alert triggers when only one PRIM is able to process the normal law, because the two other PRIMs are in degraded law, not active, or not powered.

At F/CTL LAWS REDUND LOST the law is still Normal — you have lost depth, not capability. And the FCDC cautions cost indication, never control. Per FCOM PRO-ABN-F/CTL:

This alert triggers when there is failure of both FCDCs.

Even with both data concentrators gone the aircraft flies on in Normal Law; what is lost is the F/CTL ECAM warning channel (FCDC Data Concentrators).

3.3 Law-degradation family

These two are the only cautions in the spectrum that announce a genuine law change, and they take priority over everything around them. Per FCOM PRO-ABN-F/CTL: This alert triggers when the alternate law is active. and This alert triggers when the direct law is active. The hard limits that ride with each — MAX SPEED, MAX FL, landing configuration, autoland category, USE MAN PITCH TRIM — are detailed in EFCS Computer Failures and the law articles. The triage rule: if a LAW caution is present, fly its degradation limits first, then work the accompanying cautions in ECAM order.

3.4 Input-device family

These cautions are about the pilot's input path, not the surfaces. A sidestick fault is read by the priority logic. Per FCOM PRO-ABN-F/CTL:

This alert triggers when the transducers on pitch or roll axis are failed on one sidestick.

The healthy sidestick continues to fly the aircraft; the priority and dual-input handling is in Sidestick Priority Logic.

3.5 High-lift family

The FAULT-versus-LOCKED distinction is the one to internalise. Per FCOM PRO-ABN-F/CTL:

The FLAPS FAULT alert triggers when both flaps channels fail. The FLAPS LOCKED alert triggers when the flaps wing tip brakes activate.

The SLATS FAULT alert triggers when there is a failure of both slats channels. The SLATS LOCKED alert triggers when the slats wing tip brakes are activated.

FAULT means both motor channels have failed; LOCKED means the wing-tip brakes have clamped the surface in place — a deliberate, irreversible mechanical lock against asymmetry or runaway. LOCKED is the worse outcome because the surface is no longer free to move at all. The single-SFCC cases (FLAP SYS 1(2) FAULT, SLAT SYS 1(2) FAULT) are milder: one channel of two, so the surface still drives at half speed (High-Lift Failures).

3.6 Trim / speedbrake / damping family

Most of this family is awareness-grade — a lost trim channel, an un-stowed speedbrake, an un-armed ground spoiler. Two points are worth pinning. First, the speedbrake disagree caution is a position-monitor, not a high-lift fault. Per FCOM PRO-ABN-F/CTL:

This alert triggers when the position disagrees between surfaces and handle position.

That "surfaces vs handle" wording reads like a flap/slat mismatch, but it is F/CTL SPD BRK DISAGREE — the speedbrake surfaces not matching the lever — and it maps to Spoilers, not to high-lift. Second, the turbulence-damping caution sits with the load-alleviation function. Per FCOM PRO-ABN-F/CTL:

This alert triggers when the longitudinal or lateral turbulence damping is lost due to the accelerometer failure.

Turbulence damping is a PRIM function that adds a small elevator and yaw-damper command to soften structural modes; losing the accelerometer that feeds it retires it for the flight (Load Alleviation).

3.7 Take-off configuration cross-check family

These two are not "a surface has failed" — they are the F/CTL system acting as the last configuration cross-check before brake release, comparing what the crew computed and entered against what the aircraft measures and calculates for itself. Per FCOM PRO-ABN-F/CTL:

When the TO CONFIG pb on the ECP is pressed, or when the thrust levers are set to FLEX or TOGA, there is a discrepancy between: ‐ The actual pitch trim value, and ‐ The pitch trim value entered by crew in the MCDU, and ‐ The pitch trim value calculated by the FCPC, based on the CG.

This caution is triggered when pressing the T.O CONFIG TEST pb in phase 2 or at takeoff initiation if the flap lever position and the FLAPS position as entered on the MCDU PERF T.O Page are different.

The first compares three pitch-trim values — the trim wheel's actual setting, the crew's MCDU entry, and the FCPC's own figure derived from the centre of gravity — and trips if any of them disagree, which is why its STATUS sends the crew to check the loadsheet, the FMS entries, and the trim setting. The second trips when the flap lever does not match the flap setting entered on the MCDU take-off page. Both are amber cautions that exist to catch a human entry error — a wrong loadsheet, a mis-set trim, a mistyped flap setting — before the aircraft commits to the take-off run. They live in the F/CTL volume, and a search by triggering condition (TO CONFIG pb / FLEX or TOGA) finds them, which is why they belong on this index even though nothing is broken.

[!warning]- A DISAGREE caution does not mean a surface failed — it means your entry and the aircraft's measurement do not match.

F/CTL PITCH TRIM/MCDU/CG DISAGREE and F/CTL FLAP/MCDU DISAGREE are not actuation faults; they are the take-off configuration safety net. The fault, if any, is usually in the data — a loadsheet number, an FMS entry, a trim or flap setting — not in the hardware. Treat a DISAGREE as a prompt to re-verify the loadsheet, the FMS take-off page, and the physical trim/flap settings, not as a broken THS or flap. This is the same family of protection that guards against a mis-trimmed or mis-configured take-off.

4. Using the spectrum

The index turns one caution into one decision in three steps:

1. Classify by keyword. Use the §2 mnemonic to drop the caution into one of seven families — that alone narrows the field to two or three articles.
2. Rank by degree, not by name. Within a family, the triggering condition's degree word sets the severity: one servojack versus both versus the whole surface; FAULT versus LOCKED; single SFCC versus both channels. The name is the family; the degree is the threat.
3. Give the LAW cautions priority. If F/CTL ALTN LAW or F/CTL DIRECT LAW is present, fly its degradation limits first (EFCS Computer Failures); the surface or input caution that caused the law step-down is then worked in ECAM order.

[!warning]- Sort the spectrum by triggering condition, not by alert title — titles hide.

It is tempting to build a mental list of F/CTL cautions from their names. The trap is that several cautions share or nearly share a name (ELEV SERVO FAULT / L(R) ELEV FAULT / L+R ELEV FAULT), one name means something other than it appears (RUDDER FAULT = jammed at 0°), and one caution is filed under a family its name would not suggest (SPD BRK DISAGREE reads like high-lift but is a speedbrake monitor). The reliable index is built the way this article was — by reading each caution's triggering condition and sorting on that. When you meet an unfamiliar F/CTL line in the cockpit, do the same: read the triggering logic on the STATUS/ECAM, not just the headline, before you decide what it is.

Self-test

[!note]- Q1. Into how many families does the F/CTL caution spectrum sort, and what is the fastest way to classify an unfamiliar caution?

Seven families: (1) surface/servo, (2) computer, (3) law degradation, (4) input device, (5) high-lift, (6) trim/speedbrake/damping, and (7) take-off configuration cross-check. The fastest classification is by keyword: SERVO/ELEV/AIL/RUDDER/SPLR/STAB → a surface; PRIM/SEC/FCDC → a computer; LAW → a law step-down; SIDESTICK/PEDAL/SENSOR → an input; FLAP/SLAT/TIP BRK/LEVER → high-lift; RUD TRIM/SPD BRK/GND SPLR/TURB DAMP → trim/speedbrake/damping; DISAGREE with MCDU/CG → a configuration cross-check. One keyword narrows the whole list to two or three articles. The families are a teaching structure; FCOM itself lists the cautions alphabetically.

[!note]- Q2. One elevator, three cautions — what are they and how do they differ in severity?

F/CTL ELEV SERVO FAULT triggers on loss of one servojack on one elevator — the elevator runs on its remaining servo, mild. F/CTL L(R) ELEV FAULT triggers on loss of both servojacks on one elevator — that elevator is gone, but the other elevator still works. F/CTL L+R ELEV FAULT triggers when both elevators are lost — pitch is now on the THS alone, the severe case that heads toward mechanical back-up. The headline word "ELEV FAULT" is shared; only the degree in the triggering condition (one servo / both servos / both surfaces) tells you how bad it is.

[!note]- Q3. Which F/CTL cautions mean the control law has actually degraded, and which only mean redundancy has been lost?

Only F/CTL ALTN LAW and F/CTL DIRECT LAW announce a genuine law change — degraded protections, hard speed/altitude/landing limits, and (in Direct) USE MAN PITCH TRIM. Cautions like a single F/CTL PRIM/SEC FAULT, F/CTL LAWS REDUND LOST, a single AIL SERVO/RUD B(Y)(G) SERVO FAULT, or an FCDC FAULT cost redundancy or indication while the law usually stays Normal. The triage rule follows: look for the LAW word — if it is there, fly the degradation limits first; if it is not, you have most likely lost a spare, not a capability.

[!note]- Q4. F/CTL RUDDER FAULT versus F/CTL RUD B(Y)(G) SERVO FAULT — which is the jam, and why does the distinction matter?

F/CTL RUDDER FAULT is the jam: it triggers when the rudder is detected to be faulty, or jammed, in the 0° position, and its STATUS carries MANEUVER WITH CARE, MAX X WIND FOR LDG: 15 KT, and differential-braking guidance for the landing roll. F/CTL RUD B(Y)(G) SERVO FAULT is the milder case — the blue, green, or yellow rudder servojack is lost, i.e. one of three parallel servos gone, the rudder still controllable. The distinction matters because the plain name RUDDER FAULT reads like a minor fault but is actually the jammed-rudder procedure; reading the triggering condition stops you under-reacting to it.

[!note]- Q5. What do the two DISAGREE cautions check, and where is the fault usually found?

F/CTL PITCH TRIM/MCDU/CG DISAGREE compares three pitch-trim values — the trim wheel's actual setting, the crew's MCDU entry, and the FCPC's CG-derived figure — when the TO CONFIG pb is pressed or the thrust levers go to FLEX/TOGA, and trips if any disagree. F/CTL FLAP/MCDU DISAGREE trips when the flap lever does not match the FLAPS setting entered on the MCDU take-off page. Both are configuration cross-checks run before brake release; the fault is usually in the data — a wrong loadsheet, a mis-set trim, a mistyped flap setting — so the response is to re-verify the loadsheet, FMS entries, and physical trim/flap settings, not to suspect broken hardware.

[!note]- Q6. Where do F/CTL RUDDER FAULT (jam), F/CTL STAB CTL FAULT, and F/CTL TURB DAMP FAULT each send you?

F/CTL RUDDER FAULT (rudder jammed at 0°) → Rudder and Yaw plus the QRH Jam and Loss of Control procedures. F/CTL STAB CTL FAULT (loss of the electrical control of the stabiliser) → Trimmable Horizontal Stabiliser, where the crew falls back to the manual pitch-trim wheel. F/CTL TURB DAMP FAULT (turbulence damping lost on an accelerometer failure) → Load Alleviation, the article that develops the PRIM damping function.

Key takeaways

References

Per FCOM PRO-ABN-F/CTL (the complete F/CTL caution population and each caution's verbatim Triggering Condition — surface/servo: AIL SERVO FAULT, L(R) INR(OUTR) AIL FAULT, ELEV SERVO FAULT, L(R) ELEV FAULT, L+R ELEV FAULT, ELEV REDUND LOST, RUD B(Y)(G) SERVO FAULT, RUDDER FAULT (rudder faulty/jammed at 0°, with MANEUVER WITH CARE / MAX X WIND FOR LDG 15 KT STATUS), SPLR FAULT, GND SPLR FAULT, STAB CTL FAULT; computer: PRIM 1(2)(3) FAULT, SEC 1(2) FAULT, PITCH FAULT, LAWS REDUND LOST, FCDC 1(2) FAULT, FCDC 1+2 FAULT; law: ALTN LAW, DIRECT LAW; input: L(R) SIDESTICK FAULT, PEDAL SENSOR FAULT, RUD PEDAL FAULT, SENSOR FAULT; high-lift: FLAPS FAULT/LOCKED, SLATS FAULT/LOCKED, FLAPS/SLATS FAULT/LOCKED, FLAP SYS 1(2) FAULT, SLAT SYS 1(2) FAULT, SLAT (FLAP) TIP BRK FAULT, FLAP LVR NOT ZERO, FLAPS LEVER OUT OF DETENT; trim/speedbrake/damping: RUD TRIM 1(2) FAULT, RUD TRIM FAULT, SPD BRK DISAGREE, SPD BRK FAULT, SPD BRK STILL OUT, GND SPLR NOT ARMED, TURB DAMP FAULT; take-off configuration: PITCH TRIM/MCDU/CG DISAGREE, FLAP/MCDU DISAGREE). The seven-family taxonomy and the caution-to-article mapping are an organising and indexing synthesis built on top of those verbatim triggering conditions, not a manual chapter division (FCOM lists the cautions alphabetically). Mechanisms, full ECAM procedures and STATUS limits are developed in the mapped articles: Ailerons, Elevators, Rudder and Yaw, Trimmable Horizontal Stabiliser, Spoilers, Ground Spoilers, EFCS Computer Architecture, EFCS Computer Failures, FCDC Data Concentrators, Alternate Law, Direct Law, Sidestick Priority Logic, Pilot Controls, Load Alleviation, High-Lift Overview, High-Lift Failures, Controls and Indications, and QRH Jam and Loss of Control.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.