Flight Control Data Concentrators (FCDC)

Every other computer in this chapter exists to move the aircraft. The two FCDCs exist to talk about it. While the PRIMs and SECs are reading the sidestick, computing the law, and driving the servocontrols, a parallel pair of single-channel boxes sits beside them, copies what they have computed, and forwards it to the screens, the warning system, the maintenance system, and the recorders. The FCDC issues no surface order, drives no servoloop, and takes no part in any control law. It is the flight-control system's spokesperson and medical-records clerk in one: the route by which everything the computers know becomes something the crew can see, the warning system can announce, and maintenance can trace.

That single fact re-frames the whole article, so it goes first:

[!warning]- The FCDC commands nothing. Losing both is a loss of indication and reporting, not of control.

An FCDC is a data concentrator, not a flight control computer. It reads data the PRIMs and SECs have already produced and passes it on — to the displays (EIS), the Flight Warning Computer (FWC), the Central Maintenance Computer (CMC), and the recorders. It moves no elevator, aileron, spoiler, or rudder. The most counter-intuitive consequence, drilled in §8, is that with both FCDCs failed the aircraft still flies in normal law — what you lose is the ability to see and hear the flight-control system, not the ability to fly it. If you carry a "computer fault = handling degradation" reflex into this article, the FCDC will read wrong.

1. What an FCDC is — an interface, not a controller

The pilot-facing FCOM compresses the whole subsystem into one line. Per FCOM DSC-27-10-10:

The FCDCs acquire data from the PRIMs and SECs and send this data to the EIS and CMC.

That is the skeleton: take data from the commanding computers, hand it to the displays and to maintenance. The maintenance source fleshes the same box out and, crucially, names two outlets the FCOM line omits — the warning system and the recorders. Per AMM 27-95-00:

The Flight Control Data Concentrator (FCDC) serves as an interface between the flight control computers (FCPCs and FCSCs) and the display system (EIS, FWC), the maintenance system (CMS) and the recording system (FDIU). It achieves the data concentration functions, the warning transmission and performs the flight control system maintenance.

Line the two up and the FCDC's job is fully drawn:

• Upstream are the flight control computers — the FCPCs (PRIM) and FCSCs (SEC). The FCDC reads their outputs; it does not read raw sensors.
• Downstream are four consumers — the display system (EIS, including the SD and PFD), the warning system (FWC), the maintenance system (CMC/CMS), and the recording system (FDIU).
• Between them it performs three functions: data concentration, warning transmission, and flight-control-system maintenance.

Per AMM 27-95-00, those three functions are stated explicitly:

The three main functions of the FCDC are: - Data concentration... - Warning... - Maintenance...

One sentence to carry through the whole chapter: nothing the flight control computers compute reaches a screen, a chime, the maintenance log, or the recorder except through the FCDC. That is exactly why the aircraft can fly perfectly while the crew goes blind and mute to the flight-control system (§8).

2. The architecture — inputs, the box, outputs

2.1 The interface at a glance

The conceptual layout — data sources on the left, the concentrator in the middle, consumers on the right:

   UPSTREAM (read, not generated)        FCDC                  DOWNSTREAM (consumers)

  ┌────────────────────────┐
  │  3 PRIM (FCPC)         │──┐ ARINC 429
  │  2 SEC  (FCSC)         │  │ (digital)
  └────────────────────────┘  │
  ┌────────────────────────┐  │   ╔═══════════════════╗  ARINC 429  ┌──────────────────────────┐
  │  opposite FCDC         │──┼──►║   FCDC 1 (2)      ║────────────►│ DMC / EIS   → SD + PFD    │
  │  (cross-check, DGO6)   │  │   ║   single channel  ║             │ FWC         → warnings    │
  └────────────────────────┘  │   ║                   ║             │ CMC         → maintenance │
  ┌────────────────────────┐  │   ║  1. concentrate   ║             │ FDIU / DMU  → recording   │
  │  LGCIU (ground sig.)   │──┘   ║  2. warn  (→ FWC) ║             │ FCMC / back to FCPC, FCSC │
  │  (discrete)            │      ║  3. maintain(→CMC)║             └──────────────────────────┘
  └────────────────────────┘      ╚═════════╤═════════╝
                                            │ discrete outputs (output relays)
                                            ▼
                                  ┌──────────────────────────────┐
                                  │  sidestick priority lights    │
                                  │   red / green · Capt + F/O     │
                                  │  BCM TEST                      │
                                  └──────────────────────────────┘

Four things to read off it:

1. The upstream is computers, not sensors. The FCDC does not measure angle-of-attack, does not read the raw sidestick transducers. It reads the already-computed results of the PRIMs and SECs (per FCOM, it acquires data from the PRIMs and SECs). So a "surface position" or a "protection speed" the FCDC shows is second-hand data from PRIM/SEC; the FCDC only selects and forwards it (§3).
2. The downstream digital bus serves the three functions. The FCDC's ARINC 429 outputs reach the indicating chain (DMC/EIS, feeding SD and PFD), the FWC (warnings), the CMC (maintenance) and the FDIU/DMU (recording) — and, on dedicated buses, the opposite FCDC and the originating FCPCs/FCSCs themselves. That is the physical outlet for the "concentrate / warn / maintain" functions of §3–§5.
3. The two FCDCs cross-talk. A dedicated bus (DGO6, "FCDC OPP") links FCDC 1 and FCDC 2 for comparison and cross-check. This is why, after one fails, the system still knows the other is there.
4. The discrete outputs hide a surprise. Through output relays the FCDC physically lights the sidestick priority lights and drives a BCM TEST discrete (§2.3) — it is not a pure passive display.

2.2 Component facts and interface capability

Per AMM 27-95-00 the FCDC declares itself flatly: The computer is a single channel. Hold onto that — a single channel has no internal COM/MON self-monitor, so it leans on a watchdog to catch itself, and that watchdog is allowed only a fixed number of restart attempts before the box gives up (§7).

The interface capacity, per the AMM 27-95-00 table:

"Concentrator" is a precise word, not a synonym for "relay": a single quantity — rudder position, say — often arrives from several PRIM/SEC sources, and the FCDC must pick one by validity and priority before sending it on (§3.1). Converging a trustworthy value out of redundant sources is the concentration.

2.3 The discrete outputs the FCDC actually drives

The discrete-output table is where the FCDC stops being a passive screen-feeder. Per AMM 27-95-00:

DSO01 RED PRIORITY/CAPT LIGHT ... DSO02 GREEN PRIORITY/CAPT LIGHT ... DSO04 RED PRIORITY/FO LIGHT ... DSO05 GREEN PRIORITY/FO LIGHT ... DSO08 BCM TEST.

So four of the FCDC's discrete outputs, through output relays, physically illuminate the red and green priority lights on the Captain's and First Officer's sidesticks, and another drives a BCM TEST discrete.

[!warning]- The sidestick priority lights are lit by the FCDC, not by the sidestick wiring and not by the PRIM.

Predict first: a pilot presses the takeover button, the other stick's red priority light comes on — who switched it on? Most answer "the sidestick circuit" or "the PRIM". In fact the priority logic (who has priority, whether the inputs are summed) is computed in the PRIM — see Sidestick Priority Logic — but the physical lamp is driven by the FCDC's discrete outputs through relays. The consequence is a genuine exam point: losing both FCDCs degrades the priority light indication even though the priority logic still runs in the PRIM. The FCDC holds a few real discrete control lines; it is not "just a display".

3. Function one — data concentration

The FCDC's first job is to choose the data. Per AMM 27-95-00:

The data listed below and used by the SD (System display), PFD (Primary Flight Display) and FDIU result from a selection made from different sources, as a function of their validity and according to certain priorities.

So the same datum may come from several PRIM/SEC sources, and the FCDC selects one by validity and priority, then routes the selected set to each of three consumers. Per AMM 27-95-00, what goes to each:

Two readings worth keeping:

• The PFD's protection speeds are FCDC-forwarded. The α-max, α-prot, and stall-warning speed marks on the PFD speed scale are computed by the PRIM and passed to the PFD by the FCDC. This is precisely why, in §8, a dual FCDC loss makes those speed indications disappear from the PFD — the PRIM has not stopped computing them, the FCDC has stopped forwarding them.
• Spoiler position is binary. Per AMM 27-95-00, the SD shows spoilers in binary form: extended or retracted — there is no proportional deflection bar for a spoiler the way there is for an aileron or elevator. A small but real SD-reading detail.

4. Function two — warning transmission

The second job: the FCDC feeds the Flight Warning Computer (FWC) the raw defect data, and the FWC turns it into the warnings the crew sees. The division of labour matters — the FCDC supplies the raw material; the FWC manufactures the warning. Per AMM 27-95-00:

The FCDC feeds the FWC with defect data to elaborate warnings. The warnings are divided into 3 classes: Class 1, Class 2 and Class 3.

The three classes decide when the crew is disturbed in flight and when they only learn after landing. Per AMM 27-95-00, the Class 1 levels:

Level 3: warning associated with the MASTER WARN red light and continuous repetitive chime. Level 2: caution associated with the MASTER CAUT amber light and single chime. Level 1: caution displayed alone without any other activation except a possible local warning.

Class 1 faults are shown on the Engine/Warning Display (EWD) at one of those three urgency levels. Classes 2 and 3 do not interrupt the flight at all. Per AMM 27-95-00:

...must result in the display of the F/CTL indication at the end of the flight to indicate that a maintenance action is required. ... The Class 3 faults are associated with no warning.

A Class 2 fault is one for which crew awareness during flight is not required; it surfaces only as an end-of-flight F/CTL indication, flagging maintenance. A Class 3 fault produces no warning at all and lives only in the maintenance memory.

[!warning]- The ECAM F/CTL warnings are FCDC-fed — which is why losing both FCDCs mutes them.

Every red or amber F/CTL warning you see in flight rides the chain "PRIM/SEC detect the fault → FCDC collect and classify it → feed the FWC → FWC announces it on the EWD." The FCDC is the feedstock stage. Pull it out — both FCDCs failed — and the FWC receives no flight-control defect data, so F/CTL warnings are not available on ECAM (§8). The aircraft can develop a genuine flight-control fault and ECAM will stay silent about it. One thing survives, because it runs on an independent path that does not pass through the FCDC: the stall warning is still available.

5. Function three — maintenance

The third job makes the FCDC the flight-control system's records clerk: it isolates, memorises, and locates faults down to the line-replaceable-unit level, and interfaces with the CMC. Per AMM 27-95-00:

The purpose of the maintenance function is to analyze and memorize all the system failures detected by the FCPCs and FCSCs or detected by the FCDC itself. The purpose is to locate with the highest possible accuracy the origin of the failure i.e. to have at least identification at LRU level.

Two mechanism details explain why the FCDC "remembers" faults:

• Faults are stored in non-volatile EEPROM. The functional card carries a 32-Koctet EEPROM whose contents survive a power-down. Per AMM 27-95-00: EEPROM : 32 Koctets (memory not erased in the absence of electrical power supply). The function of this memory is to store the maintenance data. This is why an intermittent fault that appeared and vanished in flight can still be pulled from the FCDC on the ground — packaged with supporting detail in the Trouble Shooting Data (TSD), per AMM 27-95-00 grouped... in the form of encoded information.
• The interactive read-out is ground-only. Maintenance retrieves the EEPROM contents through the MCDU, but per AMM 27-95-00 the interactive mode is only authorized on ground, all engines stopped — so it cannot be triggered in flight.

6. The spurious "RUD TRV LIM" on the ground

This is the FCDC's most-examined quirk, and the FCOM hangs a note on it directly after the FCDC paragraph. Per FCOM DSC-27-10-10:

On ground, a spurious "RUD TRV LIM" could be displayed on INOP SYS ECAM status page, in case of one FCDC does not detect its ground condition. This message will disappear as soon as the rudder control is pressurized by hydraulic.

The root cause links the FCOM note to the AMM engage logic (the connection itself is reasoning, flagged in References):

• The rudder travel limiter is a speed-dependent function — at high speed it caps rudder deflection to protect the fin (detail in Rudder and Yaw). On a cold, static aircraft with the rudder not yet hydraulically pressurised, that function is simply not yet active/confirmed-healthy.
• On power-up the FCDC must work out whether it is on the ground. Per AMM 27-95-00, the computer is engaged as soon as the aircraft electrical network is energized, and the start-up examination of different variables (ground, duration of power supply interrupt) with an approximately 3-second self-test sets that ground/flight state. If one FCDC fails to confirm "I am on the ground" in that window, it treats "travel limit unavailable" as a real fault and posts RUD TRV LIM on the INOP SYS list.
• Once the rudder is hydraulically pressurised — engines started, pressure built — the travel limiter goes active, the FCDC confirms healthy, and the spurious message clears, exactly as the note promises. The timing is tied to hydraulic pressurisation (ATA-29 Hydraulic Fundamentals).

[!warning]- A ground RUD TRV LIM is usually a cold-and-dark normal, not a rudder fault.

See RUD TRV LIM on the STATUS page before engine start and the first question is "is the rudder not yet pressurised?", not "is the rudder broken?". It is the visible side-effect of the FCDC's ground/flight detection on power-up, and it clears on pressurisation. Treating it as a genuine failure to be actioned is the classic trap. (The same behaviour is noted in some operators' ground procedures, which warn that the INOP SYS list "may display RUD TRV LIM" on the ground and that it clears once hydraulics pressurise the rudder after start.)

7. Inside the box — single channel, watchdog, four restarts

What the FCDC is made of decides how it fails. Its internal organisation, per AMM 27-95-00:

   32 discrete inputs   28 VDC supply   16 ARINC inputs   9 ARINC outputs
        │                    │                │                 ▲
        ▼                    ▼                ▼                 │
  ┌──────────────┐    ┌────────────┐   ┌──────────────┐   ┌──────────┐
  │ discrete in  │    │ POWER      │   │ ARINC in I/F │   │ ARINC out│
  │ acquisition  │    │ SUPPLY     │   └──────┬───────┘   └────▲─────┘
  └──────┬───────┘    │ +15/+5/    │          │                │
         │            │ +5 standby │   ┌──────▼────────────────┴───┐
  ┌──────▼───────┐    └────────────┘   │  2× ASIC "TIGRE"          │
  │ discrete out │                     │  (ARINC 429 I/O · DMA)    │
  │ → 8 relays   │    ┌──────────┐     └──────────┬───────────────┘
  └──────┬───────┘    │ WATCHDOG │◄── reset count ┤
         │            └────┬─────┘                 │
  ════════════════ COMPUTER BUS ═══════════════════╪═══════════
         │          │          │          │        │
   ┌─────▼───┐ ┌────▼───┐ ┌────▼────┐ ┌───▼─────┐ ┌▼──────────┐
   │ 68000   │ │ ASIC   │ │ REPROM  │ │ RAM     │ │ EEPROM    │
   │ 10 MHz  │ │ GLU    │ │ 512 Ko  │ │ 128 Ko  │ │ 32 Ko     │
   │ + clock │ │        │ │ program │ │ working │ │ maint.    │
   └─────────┘ └────────┘ └─────────┘ └─────────┘ └───────────┘
                                                  (kept on power-down)

Three mechanism points that matter to a pilot:

1. Single channel, watchdog-protected. Unlike a PRIM or SEC, the FCDC has no COM/MON self-checking pair. It relies on a watchdog — per AMM 27-95-00, if the program does not run normally, the watchdog is not re-activated, thus causing a reset.
2. Four restarts, then it stays down. Per AMM 27-95-00, a hardware device is provided to limit the number of such start-ups to 4. When the counter is full, the reset is no longer activated and the computer remains stalled with its outputs de-activated. The counter is reset through power supply interrupt. That is one route to a genuine F/CTL FCDC 1(2) FAULT: the box has cycled its watchdog resets to exhaustion and dropped out.
3. Power-up reads the ground state. Per AMM 27-95-00, if the power-interrupt exceeding 6s and the ground conditions are present, the start-up phase is accompanied by self-test (about 3 s). That ground determination at power-up is exactly the logic behind the spurious RUD TRV LIM of §6: the FCDC must "recognise the ground" the instant it powers up, and a miss produces the false posting.

8. The fault spectrum — losing one FCDC versus both

8.1 One FCDC — F/CTL FCDC 1(2) FAULT

Per FCOM PRO-ABN-F/CTL, the trigger and the entire procedure are minimal:

This alert triggers when there is failure of one FCDC.

The procedure body is one line — Crew awareness. — and the STATUS page shows a single INOP SYS FCDC 1(2). There is no control-law change and no handling change: you have lost one of two data concentrators, and the surviving FCDC carries the indication and warning chain on its own. (Whether a single FCDC loss affects autoland CAT 3 capability is not stated in this alert entry, so it is left open rather than inferred — see Self-test Q4.)

8.2 Both FCDCs — F/CTL FCDC 1+2 FAULT

This is the entry to memorise. Per FCOM PRO-ABN-F/CTL:

This alert triggers when there is failure of both FCDCs.

and the note that defines the consequence:

Note: ‐ Control law remains normal ‐ All information is flagged on the F/CTL SD page ‐ F/CTL warnings are not available on ECAM ‐ Stall warning is available ‐ Bank and pitch limits become amber on the PFD ‐ Vαmax, VαPROT and Vsw indications are lost on the PFD.

The procedure also restricts the speedbrake above FL 200 and redirects monitoring to the overhead panel. Per FCOM PRO-ABN-F/CTL: ABOVE FL 200: SPD BRK ... DO NOT USE, with the reason — Audio stall warning is available. It is not corrected for speed brakes extension and may come early with speed brakes out — and MONITOR F/CTL OVHD PNL (read the flight-control computer state from the overhead panel, because the screens are no longer reliable).

[!warning]- Both FCDCs lost = the aircraft goes blind and mute to flight controls, but it does not degrade — control law remains normal.

The strongest counter-intuition in this chapter: with both data concentrators gone the PRIMs and SECs keep computing normal law and driving the surfaces exactly as before — the FCDC takes no part in the control loop. What you lose is the seeing and reporting: every value on the F/CTL SD page is flagged, ECAM cannot raise F/CTL warnings, and the α-max / α-prot / stall-warning speed marks vanish from the PFD while the bank and pitch limits go amber. The muscle and the brain are intact; the eyes and the voice are gone. That is why you fall back to monitoring the overhead panel and stop using the speedbrake above FL 200 — the stall warning is still there but is no longer corrected for speedbrake extension.

9. The electrical back door — BAT ONLY costs the last FCDC

There is a second way into that same "blind and mute" state, and it has nothing to do with an FCDC breaking: a deep electrical degradation. In the ELEC EMER CONFIG Sys-Remaining table, the FLT CTL block lists only PRIM 1, SEC 1, SEC 2 and FCDC 1 — FCDC 2 does not appear, because the emergency electrical network does not feed it. So in the electrical emergency configuration the one surviving concentrator is FCDC 1, and its fate across the degradation steps, per the FCOM/QRH ELEC EMER CONFIG SYS REMAINING table:

Read three things from that row:

1. As long as the emergency generator turns, FCDC 1 stays Norm — whether the EMER GEN is driven by the engine hydraulic pumps or has dropped back to RAT-only drive (the all-engines-out case). The flight-control indication chain is still alive.
2. Drop one step further to BAT ONLY — emergency generator gone, batteries only — and FCDC 1 goes inop. With its last concentrator dead, the system holds no working FCDC at all, and the indication/warning consequences are identical to the FCDC 1+2 FAULT note of §8.
3. The law also degrades here — but for a different reason. ELEC EMER CONFIG itself runs in ALTN LAW (PROT LOST) per the ELEC EMER CONFIG summary. That degradation comes from losing PRIM/SEC computers, not from losing the FCDCs. Keep the two effects separate: the FCDC loss costs you visibility; the law change has its own cause.

[!warning]- BAT ONLY blinds the flight-control displays and degrades the law — but the two are unrelated.

It is tempting to read "the law degraded and the F/CTL screens went blind" as one event. They are two. The screens went blind because the last FCDC (FCDC 1) dropped at BAT ONLY; the law went to alternate because the electrical emergency took out flight control computers. An FCDC never moves the law — it only ever costs you the eyes and the voice. One line to keep: battery-only = flight controls go blind too, but the law degraded for its own reasons.

Dispatch and reset, in brief. The FCDC is not a flight-critical controller, so its handling on the ground is light: per the QRH system-reset table the FCDC uses the standard reset procedure (no special law-check constraint of the kind a PRIM/SEC reset carries). For dispatch, some operators' MEL allow the aircraft to depart with one FCDC (FCDC 2) inoperative under a longer repair interval — two installed, one required — while an active F/CTL FCDC 1+2 FAULT is not dispatchable. Full degradation handling and the coupling to the high-lift indication after a dual FCDC loss are developed in EFCS Computer Failures and Degradation and High-Lift Failures.

Self-test

[!note]- Q1. Does the FCDC move any control surface? What are its three functions?

No — it takes no part in any control loop. The FCDC is the interface and data concentrator between the flight control computers (FCPC/FCSC) and the display (EIS/FWC), maintenance (CMS/CMC) and recording (FDIU) systems. Its three functions are: data concentration (selecting a value from redundant PRIM/SEC sources by validity and priority, and feeding the SD, PFD and FDIU); warning transmission (feeding defect data to the FWC, which elaborates the F/CTL warnings in three classes); and maintenance (isolating and memorising faults to LRU level in non-volatile EEPROM, and interfacing with the CMC). It issues no surface order and runs no control law — the essential difference from a PRIM or SEC.

[!note]- Q2. Why are the ECAM F/CTL warnings said to be "FCDC-fed", and what happens to them if both FCDCs fail?

The warning chain is "PRIM/SEC detect the fault → FCDC collect and classify it (Class 1/2/3) → feed the FWC → FWC announces on the EWD." The FCDC only supplies the defect data; the FWC manufactures the warning. So with both FCDCs failed, F/CTL warnings are not available on ECAM — the feedstock stage is gone and the FWC receives no flight-control defect data. The stall warning is the exception: it runs on an independent path that does not pass through the FCDC, so it is still available.

[!note]- Q3. What is the root cause of a ground spurious RUD TRV LIM, and why does it clear on pressurisation?

On power-up the FCDC must determine whether it is on the ground (a roughly 3-second self-test examining the ground condition and the duration of any power interrupt). If one FCDC fails to confirm its ground state, it treats the speed-dependent rudder travel limiter as "unavailable" and posts a spurious RUD TRV LIM on the INOP SYS list. Once the engines are started and the rudder control is hydraulically pressurised, the travel limiter becomes active and the FCDC confirms healthy, so the message disappears — a cold-and-dark ground normal, not a real fault.

[!note]- Q4. What do you lose with one FCDC failed versus both, and why does control law stay normal after a dual loss?

One FCDC (F/CTL FCDC 1(2) FAULT): only a crew-awareness indication, a single INOP SYS FCDC 1(2) on STATUS, no law or handling change, no action required. (Any autoland effect is not stated in the alert entry, so it is not inferred.) Both (F/CTL FCDC 1+2 FAULT): control law remains normal — because the FCDC is not in the control loop, the PRIMs/SECs keep flying normal law — but you lose the seeing and reporting: all F/CTL SD information is flagged, ECAM has no F/CTL warnings, the PFD loses Vαmax/VαPROT/Vsw, the bank and pitch limits go amber, and the speedbrake is not to be used above FL 200. The muscle and brain remain; the eyes and voice are gone.

[!note]- Q5. Who lights the sidestick priority lights, and what does that tell you about the FCDC?

The FCDC lights them. Its discrete outputs (DSO01/02/04/05), through output relays, drive the red and green priority lights on both the Captain's and First Officer's sidesticks. The priority logic — who has priority, whether inputs are summed — is computed in the PRIM, but the physical lamp is an FCDC output. It shows the FCDC holds real discrete control lines (it also drives a BCM TEST discrete), so it is not merely a passive display — and it is why a dual FCDC loss affects the priority-light indication even though the priority logic still runs.

[!note]- Q6. In ELEC EMER CONFIG, is FCDC 1 lost when only the RAT drives the emergency generator? When is the last FCDC lost?

No. Per the ELEC EMER CONFIG SYS REMAINING table, FCDC 1 stays Norm whether the emergency generator is driven by the engine hydraulic pumps or by the RAT only. FCDC 2 is not in the table at all — the emergency network does not feed it. The last FCDC (FCDC 1) is lost only one step deeper, at BAT ONLY, where it goes inop in flight and on the ground; at that point the flight-control displays go blind exactly as in a FCDC 1+2 FAULT. The accompanying alternate law in ELEC EMER CONFIG comes from the lost flight control computers, not from the FCDCs.

Key takeaways

References

Per FCOM DSC-27-10-10 (FCDC skeleton — acquire data from the PRIMs and SECs... to the EIS and CMC; the ground spurious RUD TRV LIM note). Per AMM 27-95-00 Description and Operation (definition as interface to display/warning/maintenance/recording systems; component location — two units, panels/zones; single-channel architecture; interface capability and DSO/DGO tables; the three functions; data concentration selection and the SD/PFD/FDIU data lists incl. spoilers in binary form; warning classes 1/2/3 and Class 1 levels; maintenance function, LRU-level isolation, non-volatile EEPROM, TSD, ground-only interactive mode; internal organisation — 68000/GLU/REPROM/RAM/EEPROM/TIGRE; engage logic, watchdog, power-up ground/self-test and the four-restart limit). Per FCOM PRO-ABN-F/CTL (F/CTL FCDC 1(2) FAULT — trigger, crew awareness, INOP SYS FCDC 1(2); F/CTL FCDC 1+2 FAULT — trigger and the control law remains normal note, SPD BRK above FL 200, MONITOR F/CTL OVHD PNL, stall-warning behaviour). Per the FCOM/QRH ELEC EMER CONFIG SYS REMAINING table and ELEC EMER CONFIG summary (FCDC 1 Norm under EMER GEN incl. RAT-only, inop at BAT ONLY; FCDC 2 absent from the emergency network; ALTN LAW PROT LOST). Per the QRH system-reset table (FCDC standard reset procedure). The spoiler position-source list (ASM LGCIU-to-FCDC discrete) corroborates the LGCIU ground-signal input. Couplings flagged as reasoning — the spurious RUD TRV LIM mechanism (FCOM note + AMM ground-detection logic + rudder travel-limiter speed dependence) and the priority-logic-in-PRIM / priority-lamp-by-FCDC split — are integrative synthesis to be confirmed in the rudder and sidestick-priority articles, not single verbatim manual statements. Dispatch handling generalised from some operators' MEL.

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.