High-Lift Failures

The slats and flaps fail in a way the primary flight controls never can. An aileron, an elevator, a spoiler — each is a distributed, independent surface; lose one and the others carry on. The high-lift system is the opposite: one Power Control Unit on the fuselage centreline drives both wings through a single torque shaft, so the two sides are mechanically forced to move together. That central-drive, symmetric-transmission design has one dominant failure mode and one dominant fear — asymmetry: if one side's transmission breaks or jams while the other keeps moving, the wings develop unequal lift and a powerful, possibly uncontrollable, rolling moment near the ground.

The whole protection philosophy of the system reduces to a single sentence: freeze both sides rather than let one move while the other does not. The hardware that enforces it is the Wing Tip Brake (WTB) — one near each wing-tip end of the shaft. The moment the Slat and Flap Control Computers (SFCC) detect asymmetry, runaway, or over-speed, they de-energise the WTB and it locks the entire torque shaft mechanically at its current position — and cannot be released in flight. That is exactly what the ECAM word LOCKED means: a WTB has fired.

This article covers how high-lift breaks, what each ECAM alert is actually telling you, and how you fly the result. It is the failure-and-procedure companion to the high-lift mechanism articles (High-Lift Overview, Flap System, Slat System); the full QRH numerical procedure — landing weights, the speed-increment schedule, landing-distance factors — is worked in QRH Jam and Loss of Control.

Two re-framings up front, because they change how every alert below reads:

[!warning]- LOCKED is a protection that has fired, not a worse fault than FAULT. And it is irreversible in the air.

The intuitive ranking — "FAULT is the problem, LOCKED is a smaller sub-case" — is backwards. FAULT means the electrical control has been lost (both channels of one surface failed). LOCKED means the system caught a transmission problem and deliberately braked the shaft solid to stop an asymmetry developing — the WTB doing its job. The crucial operational fact is that a WTB latch resets only on the ground: no amount of lever movement will free it in flight. So the instant you see LOCKED, stop expecting that surface to move again — the configuration you have is your landing configuration.

[!warning]- High-lift failures are level-2 cautions only — there is no red (level 3) warning for slats or flaps.

Per AMM 27-81-00, Failures in the slat system will not give any level 3 warnings. The Electronic Instrumentation System (EIS) system shows level 2 cautions to the flight crew. The flap system is identical. A jammed, locked, or half-speed high-lift system is never an immediate red-warning emergency; it is an amber caution you manage by configuring carefully and landing with what you have. The danger it guards against — asymmetry — has already been removed by the lock. So read every alert in this article as "manage the landing", not "imminent loss of control".

1. The architectural premise — why asymmetry is the one fatal mode

Recall the drive train from High-Lift Overview: one lever, read by the Command Sensor Unit (CSU); two SFCCs; one PCU per surface (two hydraulic motors + a differential gearbox); a span-wise torque shaft running out to both wings; and at each wing tip an Asymmetry Position Pick-Off Unit (APPU) and a WTB. A central Feedback Position Pick-Off Unit (FPPU) sits at the PCU. Per AMM 27-51-00, the flap chain is built from exactly this list:

The electrical control and monitoring system of the flaps has: ‐ a manually operated slat/flap control lever, ‐ a Command Sensor Unit (CSU) ... ‐ two Slat and Flap Control Computers (SFCC1 and SFCC2) ... ‐ a Feedback Position Pick-Off Unit (FPPU) ... ‐ two Asymmetry Position Pick-Off Units (APPU) ... ‐ two Wing Tip Brakes (WTB) ... ‐ two flap interconnecting struts, each with two disconnect proximity switches ... ‐ two track 4 sensor struts ...

Two facts about that topology drive everything in this article:

• One PCU feeds two wings through one shaft. In normal operation the left and right surfaces are rigidly synchronised — they take the same rotation of the same shaft. The only way to go asymmetric is a mechanical break or jam somewhere in the transmission. This is why a lost hydraulic system makes high-lift slow, not crooked — losing one of the PCU's two motors only drops the shaft to half speed; both wings still move together. Real asymmetry comes from broken metal, not lost pressure.
• The watchdogs live at the tips. Because the APPU sits at the far end of each side's shaft, a slip or jam anywhere in between shows up as the largest possible left-versus-right divergence — the most sensitive place to measure asymmetry.

         left wing tip                CENTRELINE                right wing tip
    ┌────────────────────┐      ┌──────────────────┐      ┌────────────────────┐
    │  APPU(LH) ── WTB ──┼─shaft┤    PCU (1 unit)   ├shaft─┼── WTB ── APPU(RH)  │
    └─────────┬──────────┘      │  2 motors + diff  │      └─────────┬──────────┘
              │                 │  gearbox · POB    │                │
              │                 │  FPPU (central)   │                │
              │                 └───────┬───────────┘                │
              │                         │                            │
              ▼                         ▼                            ▼
    ┌─────────────────────────────────────────────────────────────────────────┐
    │  SFCC 1            SFCC 2          (each = 1 slat + 1 flap channel)        │
    │  • compare LH APPU vs RH APPU ........... asymmetry?                       │
    │  • compare APPU vs FPPU ................. runaway?                         │
    │  • compare actual vs CSU command ........ uncommanded movement?           │
    │  • if confirmed → de-energise WTB → torque shaft LOCKED (= ECAM LOCKED)   │
    └───────────────────────────────────────────────────────────────────────────┘
              ▲ CSU (lever)                              ▲ disconnect / track-4 (flap only)

The reader's takeaway is not the sensor names but the philosophy: the system would rather wrongly freeze a healthy side than tolerate any asymmetry. So LOCKED is the design working as intended, not a deeper malfunction.

2. What the SFCC watches — the monitored failure conditions

The SFCCs continuously compare position data to find transmission faults. Per AMM 27-81-00, the slat chain is monitored for seven conditions:

The SFCCs monitor the power transmission system for these failure conditions: ‐ asymmetry (a position difference between the two APPU), ‐ runaway (a position difference between the APPUs and the FPPU), ‐ uncommanded movement (a movement in the wrong direction, or movement away from the last commanded position), ‐ overspeed, ‐ system jam, ‐ half speed, ‐ low hydraulic pressure.

The flap chain adds two local monitors the slat chain does not have — flap disconnect and flap track 4 sensor displacement (the interconnecting-strut and track-4 sensors detailed in Flap System) — but the comparison logic is identical. The key is what is compared against what:

Not every condition latches the WTB. There are two tiers of "stop". Per AMM 27-51-00:

The POBs of the PCU and in some cases the WTBs stop and hold the transmission system when a failure in the operation of the flaps is identified.

Read that "in some cases" carefully. The lighter response is the Pressure-Off Brake (POB) inside the PCU — the routine in-position brake that simply holds the motor output. The severe asymmetry / runaway / over-speed cases escalate to the WTB, which clamps the whole torque shaft at the tip. POB = normal hold at the source; WTB = emergency latch at the tip. Only the second one shows as ECAM LOCKED.

3. The wing-tip brake — why LOCKED is irreversible, and how it resets

The WTB is a spring-applied, hydraulically-released disc brake — fail-safe in the truest sense: remove power or pressure and it bites. Per AMM 27-51-00:

The Wing Tip Brakes ... are electrohydraulic pressure-off disc-brakes. Each WTB has: ‐ a central housing which has two hydraulic manifolds, ‐ a friction disc pack, ‐ a through torque shaft, ‐ two annular pistons, ‐ two solenoid valves, ‐ two electrical connectors, ‐ a proximity switch.

and the operating logic:

When the solenoids are energized, the fluid pressure moves the piston to release the spring force holding the brake on. When the solenoids are de-energized, the fluid pressure returns through the solenoid valves. ... If hydraulic pressure is not available to one piston, the remaining piston gives sufficient force to act against the spring and let the brake off.

Three things fall out of that hardware:

1. De-energised = clamped. In normal flight the solenoids are energised and pressure holds the brake released, so the shaft turns freely. When the SFCC judges a fault it removes power, the spring drives the friction discs together, and the shaft is locked. "Lose control → lock", never "lose control → run free" — the same philosophy as §1.
2. Dual piston, dual hydraulic = no false bite. Each WTB is fed by two hydraulic systems (slats use Blue + Green, flaps use Green + Yellow), one per piston, and either one alone can hold the brake off. So losing a single hydraulic system cannot accidentally clamp a healthy shaft — a deliberate guard against nuisance locks.
3. The proximity switch is ground-test only. It confirms disc-pack position during the on-ground WTB engagement test and plays no part in in-flight fault judging.

The reset paths are what make LOCKED permanent in the air. Per AMM 27-81-00:

The circuit can be set again (reset) in different ways through the Central Maintenance System (CMS), the slat/flap lever recycle, or the SFCC reset. ... A manual release is installed in the WTB which release the brake for maintenance.

The manual release has, per AMM 27-51-00, two positions, a 'M' (Maintenance) position and an 'O' (Operation) position — a ground-maintenance device, not a flight-deck control.

[!warning]- Some high-lift faults can be cleared in flight by a lever recycle — but a confirmed WTB latch cannot.

A common over-generalisation is "any high-lift fault is unrecoverable in flight". Not so. A clearable condition such as a system jam presents with a FLAP LEVER RECYCLE prompt: returning the lever to the previous detent and back can clear it and restore operation. But once a confirmed asymmetry / runaway / over-speed has latched the WTB into LOCKED, the lever-recycle path no longer helps — that reset needs the CMS or an SFCC reset on the ground. The discriminator is whether the ECAM offers FLAP LEVER RECYCLE: if it does, try once; if the alert is LOCKED, accept the configuration and plan the landing.

4. The ECAM alert spectrum

Each F/CTL high-lift alert is defined by its triggering condition, not by guessing from the title. The table reads the alerts straight off the FCOM triggering-condition text:

4.1 FAULT versus LOCKED — the distinction to drill

This is the one to pin down. 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.

• FLAPS FAULT = electrical control lost. Both SFCC flap channels are dead, so nothing commands the PCU valve blocks. The flaps stop where they are, but no WTB has latched.
• FLAPS LOCKED = mechanically latched. The SFCC caught asymmetry / runaway / over-speed and fired the WTB. The flaps are frozen at the current angle until ground maintenance releases the brake.

The mental shift matters. On FAULT you think "an electrical box has failed"; on LOCKED you must immediately think "the brake has bitten — this is my landing configuration." Either way FCOM routes you straight to the jammed-landing technique. Per FCOM PRO-ABN-F_CTL:

For landing with flaps jammed, see OPERATING TECHNIQUES (Refer to PRO-ABN-F_CTL [QRH] Landing with Slats or Flaps Jammed).

The autopilot may be used down to 500 ft AGL. As it is not tuned for the abnormal configuration, its behavior can be less than optimum and must be monitored.

Remember that 500 ft AGL boundary: the AP is available but un-tuned for the abnormal configuration, so it is used and monitored, not trusted.

4.2 FLAP SYS 1(2) FAULT — one SFCC down, half speed, and a GPWS knock-on

Seeing F/CTL FLAP SYS 1 FAULT looks alarming but is the mildest high-lift fault. Per FCOM PRO-ABN-F_CTL it triggers when there is failure of flap channel in one SFCC — just one of the two SFCC flap channels. The flaps still extend and retract; they only run at half speed, because the PCU's differential gearbox is now driven by one motor instead of two (the half-speed mechanism is developed in Flap System). You see FLAPS SLOW and simply start configuring earlier.

The point not to miss is the cross-system knock-on to ground-proximity warning. Per FCOM PRO-ABN-F_CTL:

In case of FLAP SYS 1 FAULT: GPWS FLAP MODE ... OFF. Flap position signal to GPWS is lost. Note: If the GPWS FLAP MODE is selected OFF when the aircraft airspeed is above 250 kt, the FAULT light of the GPWS SYS pb-sw comes on. Only the GPWS modes that require flap information are lost (i.e. mode 2A and mode 4B).

So the procedure has you select GPWS FLAP MODE OFF because the flap-position feed to GPWS is no longer trustworthy. Two details to expect and not mis-read: above 250 kt that selection lights the GPWS SYS FAULT light (normal, not a new failure), and only the flap-dependent modes (2A and 4B) are lost. This is the classic "a fault in one system spills into another" — flap position is a shared upstream variable.

5. Speeds are recomputed to the actual position

The single most useful thing the system does for you after a jam is recompute the PFD speed protections against where the surfaces actually are, not where the lever sits. Per FCOM PRO-ABN-F_CTL:

Note: The OVERSPEED alert and VLS displayed on the PFD, are computed according to the actual flaps/slats position. Disregard VFE, VFE NEXT displayed on PFD.

This is protective, not pedantic. If you have selected FLAPS 2 but the slats are jammed at 0, the system does not give you the slow-flying low-speed protection that a true CONF 2 would allow — at that real angle of attack you would be near the stall. Instead it computes a higher VLS and earlier over-speed protection appropriate to the clean wing you actually have. The airmanship is therefore: trust the PFD speed scale; do not fly the speeds you remember for the configuration you selected. The associated ECAM MAX SPEED values, by actual position, per FCOM PRO-ABN-F_CTL:

This figure gives the MAX SPEED value displayed on ECAM in case of failure for all Slats/Flaps positions.

The trend is the whole lesson: the less high-lift you have out, the more you add to the reference speed — slats 0 / flaps 0 (a clean leading edge) gives VREF + 50, while full extension lands at VREF. The complete use of this table with landing distance and the weight ceiling is in QRH Jam and Loss of Control.

[!warning]- "Trust the PFD speed scale" has one fatal exception: a FLAPS FAULT caused by a dual SFCC failure loses the PFD speed limits entirely.

A plain jam (LOCKED) leaves the PFD computing VLS and the over-speed line from the actual position, so following the speed scale is correct. But if the FLAPS FAULT is the result of both SFCCs failing, the control law drops to Alternate Law and the speed protections go with it. Per FCOM PRO-ABN-F_CTL: If there is a F/CTL FLAPS FAULT after a dual SFCC failure, ALTN law becomes active (Refer to PRO-ABN-F_CTL F/CTL ALTN LAW (PROT LOST)). Speed limits are lost on PFD. In that case you can no longer lean on the speed scale — you fly the Alternate-Law hard limit, and the associated procedure gives a fixed ceiling. Per FCOM PRO-ABN-F_CTL, the F/CTL ALTN LAW (PROT LOST) procedure sets MAX SPEED ... 330/0.82. One line to fix: jam → trust the speed scale; dual-SFCC FLAPS FAULT → speed scale gone, fly ALTN law, MAX 330/0.82. The tell is that the dual-SFCC case annunciates F/CTL ALTN LAW alongside the FLAPS fault. Alternate Law itself is covered in Alternate Law.

6. The altitude alerts — 22 000 ft and the 20 000 ft diversion ceiling

A non-zero high-lift configuration belongs at low altitude and low airspeed. The system enforces that with a dedicated alert. Per FCOM PRO-ABN-F_CTL:

This alert triggers when the slat or flap lever is not in the zero position and altitude is above 22 000 ft.

Carrying slats or flaps above 22 000 ft means either you forgot to retract or they are jammed extended — in both cases continuing to climb adds drag (more fuel) and risks over-speeding the configuration's VFE. The alert and the actual-position speed recomputation of §5 are a matched pair of safety nets — one minds the speed, the other minds the altitude — both keeping a damaged configuration out of an envelope it should not enter.

The FCTM closes the loop on the technique side by capping a diversion. Per FCTM PR-AEP-F_CTL:

Consider the fuel available and the increased consumption associated with a diversion when flying with flaps and/or slats jammed. Additionally, when diverting with flaps/slats extended, cruise altitude is limited to 20 000 ft.

So if you must divert with high-lift stuck out, plan for both the higher fuel burn and a 20 000 ft cruise ceiling — you cannot climb high to save fuel, and the FMS predictions are unreliable because, per FCTM, they do not take into account the slat or flap failures.

7. The FCTM technique — three causes, late detection, and how you fly it

FCOM tells you what each alert is; FCTM tells you what causes high-lift failures, when they bite, and how to handle the approach.

7.1 Only three root causes

FCTM collapses the whole list of ECAM titles into three underlying problems. Per FCTM PR-AEP-F_CTL:

Abnormal operation of the flaps and/or slats may be due to one of the following problems: ‐ Double SFCC failure ‐ Double hydraulic failure (B+G or Y+G) ‐ Flaps/Slats jammed (operation of the WTB)

Mapping back: the double SFCC failure is the FLAPS FAULT that takes you into Alternate Law (§5 callout); the jam is LOCKED (WTB fired); and the often-overlooked middle case is a double hydraulic failure (B+G or Y+G) — because the PCU motors are hydraulically driven, losing the two systems that feed a surface stops it just as a jam would. Remembering these three causes is more useful than memorising the alert titles. FCTM also lists the consequences that follow: per FCTM PR-AEP-F_CTL, The control laws may change, The selected speed must be used, an early stabilised approach is preferred, approach attitudes change, approach speeds and landing distances increase, and the go-around may have to be modified.

7.2 The fault shows up only when you select the flaps

A counter-intuitive timing point. Per FCTM PR-AEP-F_CTL:

The detection of a slat or flap failure occurs with the selection of flap lever during the approach.

A latent problem — a dead channel, a partly-failed transmission — is invisible in the cruise with the lever at 0. It is the first approach selection that drives the system, compares the sensors, and surfaces the fault. So the typical script is "ECAM jumps the moment I configure on approach", not "a warning in the cruise" — which means a tight time window, with the aircraft already in the approach.

7.3 First reflex — pull the speed knob for selected speed

Because the fault appears as you configure, your first action is to take control of the speed before the autothrust chases the next manoeuvring speed. Per FCTM PR-AEP-F_CTL, on the approach:

At this stage, if a slat or flap failure occurs, the crew will: ‐ Pull the speed knob for selected speed to avoid further deceleration ‐ Delay the approach to complete the ECAM procedure ‐ Refer to LANDING WITH FLAPS OR SLATS JAMMED QRH procedure. ‐ Update the arrival briefing.

With A/THR managed, selecting the lever toward 1 makes the speed target the next characteristic speed (e.g. S speed), so the thrust would keep decelerating you toward a speed your jammed configuration cannot safely hold. Pulling for selected speed pins the speed so you can work the ECAM and QRH calmly. The same reflex applies at take-off. Per FCTM PR-AEP-F_CTL:

Should a flap/slat retraction problem occur at takeoff, the crew will pull the speed knob for selected speed to stop the acceleration and avoid exceeding VFE. The overspeed warning is computed according to the actual slats/flaps position.

7.4 The signature counter-intuitive move — slats jammed at 0, change configuration above VFE

The standing rule is "never exceed VFE". The jammed-slats case carries the one sanctioned exception. Per FCTM PR-AEP-F_CTL:

This procedure may involve reducing speed below the manoeuvring speed for the current configuration which is acceptable provided the speed is kept above VLS except if required by the procedure. In case of slats jammed at 0°, the configuration change is performed intentionally above VFE in order to increase margin to high Angle Of Attack situation. There is no risk of flaps structural overload.

[!warning]- With the slats jammed at 0°, the threat is the stall, not structural over-speed — so the procedure deliberately changes configuration above VFE.

Everyday airmanship treats VFE as inviolable because it is the configuration's structural speed limit. But a clean leading edge (slats 0°) has a low critical angle of attack, so the real hazard is approaching a high-AoA stall when slow — not over-stressing a flap. FCTM therefore has you make the configuration change intentionally above VFE to increase the margin to a high-AoA situation, and states plainly that there is no risk of flaps structural overload at that point (the flaps are not carrying the corresponding load). This is the high-lift system's signature "counter-intuitive but correct" action — and it is strictly limited to slats jammed at 0° when the procedure calls for it, never a general licence to exceed VFE. FCTM adds that speed and configuration changes should preferably be carried out wings level.

7.5 Flying the approach and landing

With the speeds recomputed to actual position (§5), the approach speed follows directly. Per FCTM PR-AEP-F_CTL:

Assuming VLS is displayed on the PFD, VAPP should be close to VLS + wind correction, since this speed is computed on the actual slat/flap position.

For the most extreme case — both surfaces stuck clean — the QRH NO FLAPS NO SLATS LANDING applies, and FCTM highlights its character: more distance is needed for manoeuvring, the autopilot is allowed down to 500 ft AGL, and at 500 ft you reduce to reach VLS −5 kt (or VREF +45 kt, if VLS not available) at touchdown. Because the approach attitude is high, FCTM warns of tail-strike risk — only a small pitch adjustment in the flare — and, given the high touchdown speed, that a prolonged float should be avoided. FCTM classifies a no-flaps-no-slats landing as extremely improbable, which is why it lives only in the QRH and not on the ECAM (full numbers in QRH Jam and Loss of Control).

8. Failure handling — scene by scene

The mental script for each common case:

1. F/CTL FLAPS LOCKED selecting FLAPS 1 on approach. First reflex: pull for selected speed to stop the A/THR chasing the next speed. Recognise the WTB has fired — flaps frozen, this is the landing configuration. Run the ECAM, delay the approach, go to the QRH jammed-landing case, fly the PFD's recomputed VLS / over-speed (VAPP ≈ VLS + wind correction), AP usable to 500 ft AGL but monitored. If F/CTL ALTN LAW annunciates with it (a dual-SFCC FLAPS FAULT), the PFD speed limits are gone — fly Alternate Law, MAX 330/0.82.
2. F/CTL FLAP SYS 1 FAULT. The mild one: flaps run at half speed, still fully usable. Select GPWS FLAP MODE OFF as the procedure directs (above 250 kt the GPWS SYS FAULT light coming on is normal; only modes 2A / 4B are lost). Land in a normal configuration, just allow extra time to extend.
3. F/CTL SLATS LOCKED, slats jammed at 0°. The least-favourable case (clean leading edge). Manoeuvre with care, change configuration intentionally above VFE only as the procedure requires (increasing high-AoA margin, no structural risk), expect reference speeds up toward the VREF + 50 band, a reduced landing-weight ceiling (per the QRH), and a longer landing distance.
4. High-altitude alert (lever not at zero above 22 000 ft). Check whether it was simply not retracted or is jammed; if jammed, handle per the relevant LOCKED / FAULT alert and keep the speed below the actual configuration's VFE; for a diversion, plan to the 20 000 ft ceiling and the higher fuel burn.
5. F/CTL FLAPS/SLATS FAULT/LOCKED, both stuck at CONF 0. Go to the QRH NO FLAPS NO SLATS LANDING: high approach attitude (tail-strike awareness), GPWS FLAP MODE OFF, AP to 500 ft, target VLS −5 / VREF + 45 at touchdown, no prolonged float, much longer landing distance.
6. A single WTB reported failed. That wing has lost its lock capability; it does not by itself stop extension or retraction, but it thins the asymmetry-protection redundancy — handle per ECAM/MEL.

This is the same disciplined read used across the failure articles: Which root cause — SFCC, hydraulics, or jam? Has the WTB latched (movable or not)? Which speeds does the PFD now compute? What does the QRH ask? — placed in the wider F/CTL picture in Control Surface Fault Spectrum, and distinguished from the slat alpha/speed lock (a different retraction inhibit) in Slat Alpha/Speed Lock.

Self-test

[!note]- Q1. FLAPS FAULT and FLAPS LOCKED — what is the essential difference, and which is irreversible in flight?

FLAPS FAULT means both flap channels have failed — electrical control is lost, the flaps stop, but no WTB has latched. FLAPS LOCKED means the flaps wing tip brakes have activated — the SFCC caught asymmetry / runaway / over-speed and braked the torque shaft solid. The LOCKED state is the irreversible one: a WTB resets only on the ground (CMS or SFCC reset), so in flight no lever movement frees it. Treat LOCKED as "this is my landing configuration." Counter-intuitively, LOCKED is not a worse fault than FAULT — it is a protection that has fired correctly.

[!note]- Q2. Why is asymmetry the high-lift system's most dangerous failure, and how is it detected and contained?

Because one PCU drives both wings through a single torque shaft, the surfaces are normally locked in step; if one side's transmission breaks or jams while the other moves, the wings produce unequal lift and a strong rolling moment near the ground. The SFCCs detect it by comparing the left APPU against the right APPU (a position difference = asymmetry), and by comparing the APPU against the central FPPU (= runaway). On a confirmed fault they de-energise the WTB, whose springs clamp the shaft — freezing both sides rather than allowing one to move alone. A lost hydraulic system, by contrast, makes the system slow, not crooked: both wings still move together at half speed.

[!note]- Q3. FLAP SYS 1 FAULT — why do the flaps still work, and what is the GPWS knock-on?

Only one SFCC's flap channel has failed, so one of the PCU's two motors is still driven; through the differential gearbox the flaps still extend and retract, just at half speed (FLAPS SLOW). The knock-on is that the flap-position feed to GPWS is lost, so the procedure has you select GPWS FLAP MODE OFF. Above 250 kt that selection lights the GPWS SYS FAULT light (normal), and only the flap-dependent GPWS modes — 2A and 4B — are lost. Start configuring earlier to allow for the slower travel.

[!note]- Q4. After a jam, does the PFD compute VLS and the over-speed line from the selected configuration or the actual position — and is there an exception?

From the actual slats/flaps position, per FCOM: the OVERSPEED alert and VLS displayed on the PFD are computed according to the actual flaps/slats position. So trust the speed scale rather than the speeds you remember for the lever position — at slats 0 / flaps 0 that means VREF + 50, falling to VREF at full extension. The exception: if the FLAPS FAULT follows a dual SFCC failure, Alternate Law becomes active and the speed limits are lost on PFD — then you fly the Alternate-Law limit, MAX 330/0.82, not the speed scale.

[!note]- Q5. With the slats jammed at 0°, why does FCTM have you change configuration above VFE — and is this a general permission?

Because a clean leading edge has a low critical angle of attack, so the real hazard when slow is a high-AoA stall, not structural over-speed. FCTM states the configuration change is performed intentionally above VFE in order to increase margin to high Angle Of Attack situation, and that there is no risk of flaps structural overload (the flaps are not carrying the corresponding load). It is the signature counter-intuitive move of high-lift handling, and it is strictly limited to slats jammed at 0° when the procedure requires it — never a general licence to exceed VFE.

[!note]- Q6. What are the three root causes of abnormal high-lift operation, and when does the failure usually reveal itself?

Per FCTM, only three: double SFCC failure, double hydraulic failure (B+G or Y+G), and a jam (operation of the WTB). Detection usually occurs with the selection of flap lever during the approach — a latent fault is invisible at the cruise CONF 0 and only surfaces when you first command the surfaces. So the typical script is "ECAM jumps as I configure on approach", under time pressure, and the first reflex is to pull the speed knob for selected speed to stop the autothrust before working the ECAM and QRH.

Key takeaways

High-lift failures are, in the end, one idea seen from the cockpit: the system would rather lock both wings than let them diverge, so when it locks you stop fighting for movement and start managing a careful, faster, longer landing in the configuration you have.

References

Per FCOM PRO-ABN-F_CTL (F/CTL FLAPS FAULT/LOCKED triggering conditions; AP usable to 500 ft AGL; landing-with-flaps-jammed routing; F/CTL FLAP SYS 1(2) FAULT trigger and GPWS FLAP MODE OFF / 250 kt / modes 2A & 4B; OVERSPEED and VLS computed to actual position; ECAM MAX SPEED-by-position figure; dual-SFCC FLAPS FAULT → ALTN law, speed limits lost on PFD; F/CTL ALTN LAW (PROT LOST) MAX SPEED 330/0.82; non-zero lever above 22 000 ft alert; [QRH] Landing with Slats or Flaps Jammed). Per FCTM PR-AEP-F_CTL (Abnormal Slats/Flaps Configuration — three causes: double SFCC / double hydraulic B+G or Y+G / jam; consequences incl. control-law change and use of selected speed; FMS predictions not valid; detection on flap-lever selection during the approach; pull speed knob for selected speed at take-off and approach; reduce below manoeuvring speed but keep above VLS; slats jammed at 0° → configuration change above VFE for high-AoA margin, no flap structural overload; changes preferably wings level; VAPP ≈ VLS + wind correction; diversion cruise altitude limited to 20 000 ft; NO FLAPS NO SLATS LANDING — AP to 500 ft, VLS −5 / VREF + 45 at touchdown, tail-strike awareness, avoid prolonged float). Per AMM 27-51-00 (Flaps electrical control and monitoring — system component list; POBs and in some cases the WTBs stop and hold the transmission; nine monitored conditions incl. flap disconnect and track 4; WTB electrohydraulic pressure-off disc-brake structure, energise/de-energise logic, single-piston brake-off, ground-test proximity switch, manual release M/O positions). Per AMM 27-81-00 (Slats electrical control and monitoring — seven monitored transmission conditions and the APPU-vs-APPU / APPU-vs-FPPU comparison logic; no level-3 warnings, level-2 cautions only; WTB control, de-energise-to-lock, reset via CMS / lever recycle / SFCC reset; Blue + Green WTB supply). Mechanism background per High-Lift Overview, Flap System, Slat System; Alternate Law per Alternate Law; full QRH numerical procedure per QRH Jam and Loss of Control. Framing statements — that LOCKED is "a protection that has fired", the two-net pairing of the 22 000 ft alert with the actual-position speed recomputation, and the per-scene mental scripts — are integrative synthesis from the cited passages, not verbatim manual statements.

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.