FADEC — Full-Authority Digital Engine Control

The overview called the FADEC the engine's digital brain; Three-Spool Architecture gave the hardware it manages. This article opens the brain itself: what it reads, what it drives, how its two channels stay redundant, what the EIVMU/EIU does in between, and how it degrades when that interface is lost. This underpins every later "and the FADEC responds by…" in the chapter.

1. What the FADEC is

Each powerplant has a FADEC (Full Authority Digital Engine Control) system. FADEC is a digital control system that performs complete engine management. FADEC has two-channel redundancy, with one channel active and one standby. If one channel fails, the other automatically takes control. The system has a magnetic alternator for an internal power source. FADEC is mounted on the fan case. The Engine Interface Unit (EIVMU/EIU) transmits the data it uses for engine management to the FADEC.

Per FCOM DSC-70-20: one FADEC per engine, two-channel (one active, one standby; a channel failure is taken over automatically), self-powered by a magnetic alternator, mounted on the fan case, and fed flight-side data through the EIVMU/EIU.

[!note]- FADEC and EEC are the same thing On the architecture diagram the FADEC box is annotated (EEC) = Electronic Engine Control. FADEC is the name for the full-authority digital control system; EEC is its core computing unit. For the pilot they are one object.

2. Signal topology — three sides

Per the FADEC/EIVMU architecture, signals fall into three groups: flight-side inputs (most via the EIVMU), engine sensors, and outputs to actuators and ECAM.

 [pilot controls / aircraft systems] ─┐
                                       ├─► EIVMU ──► FADEC ──► [actuators + ECAM]
 [engine sensors] ─────────────────────┘            (EEC)
   (TLA / ADIRS / N1 MODE go straight to the FADEC, not via the EIVMU)

Inputs via the EIVMU:

Inputs straight to the FADEC (not via EIVMU): Thrust-Lever Angle (TLA, the thrust request), ADIRS 1+2 (air data), N1 MODE panel (N1 backup-mode selection).

Engine sensors → FADEC: pressures/temperatures PO(PAMB), P2/T2(fan), P3/T3 and T2.5(HPC), P5/T5(LPT); speeds N1, N2, and N3 via the PCU; EGT; plus position feedback from the FMV, VIGV/VSV, IP8/HP3 bleed valves and LP/IP TCC.

FADEC outputs:

The picture in one line: the FADEC manages almost everything on the engine, and the pilot's TLA + MASTER are just two of its many inputs. That is "Full Authority."

3. Two-channel redundancy

DSC-70-20 verbatim: one channel active, one standby, the other taking over automatically on failure. Two pilot consequences:

1. A single-channel failure normally needs no crew action — the FADEC switches itself, possibly with only an ECAM advisory (see ENG CTL SYS FAULT).
2. The magnetic alternator means the FADEC self-powers once the engine turns — one basis for engine control remaining available during relight (21) and all-engines failure (31).

4. The EIVMU / EIU role

[!note]- Only the part of the EIVMU/EIU name the source gives DSC-70-20 writes "the Engine Interface Unit (EIVMU/EIU)" — i.e. EIU = Engine Interface Unit, forwarding flight-side data to the FADEC. The expansion of "VM" in EIVMU is not given at this source, so it is not inferred here; it is resolved in Engine Vibration from AMM-77. For now: the EIVMU/EIU is the interface/forwarding unit between the FADEC and the aircraft (pilot controls + ZONE CONT/LGCIU/SFCC/FMGS all reach the FADEC through it).

5. EIVMU/EIU failure — the backup

In the case of EIVMU/EIU failure, the FADEC uses a backup signal from the ENG MASTER lever and the alternate start/ignition signal to control: ‐ An automatic start, or ‐ A dry crank, or ‐ Continuous ignition. Manual starting is no longer available.

Per DSC-70-80-40, an EIVMU/EIU failure does not remove start capability — automatic start, dry crank and continuous ignition remain (the FADEC listens directly to the ENG MASTER lever) — but manual starting is lost. Degradation, not loss.

6. Counterintuitive points

[!warning]- A single FADEC channel failure leaves the engine running normally Two channels, one active one standby, the other taking over automatically (DSC-70-20). The engine usually keeps running with no crew action, perhaps just an ECAM advisory. "FADEC fault" is not "engine fault" — see 17.

[!warning]- An EIVMU failure costs "manual start," not "start" After an EIVMU/EIU failure, automatic start / dry crank / continuous ignition still work (FADEC on the ENG MASTER backup signal); only manual starting is lost (DSC-70-80-40).

Self-test

[!note]- Q1. What does FADEC stand for, how many per engine, how many channels? Full Authority Digital Engine Control, one per engine, two channels (one active, one standby, automatic takeover).

[!note]- Q2. Does losing aircraft electrical power stop the FADEC? Not necessarily — the FADEC has a magnetic alternator and self-powers once the engine is turning (basis for relight / all-engines-failure control availability).

[!note]- Q3. Do the thrust lever and ENG MASTER reach the FADEC the same way? No: TLA goes straight to the FADEC; ENG MASTER goes via the EIVMU (falling back to a direct ENG MASTER signal if the EIVMU fails).

[!note]- Q4. Name four actuators the FADEC drives. FMU (FMV/HPV), VSV/VIGV control unit, ignition system, start valve, thrust reverser, thermal management, ECAM displays.

[!note]- Q5. What start capability remains after an EIVMU/EIU failure? Automatic start / dry crank / continuous ignition remain; manual starting is lost.

Key takeaways

References

• FCOM DSC-70-20 — FADEC full authority, two-channel redundancy, magnetic alternator, fan-case mounting, EIVMU/EIU interface.
• FCOM DSC-70-80-40 — EIVMU/EIU failure backup: automatic start / dry crank / continuous ignition retained, manual start lost.
• FADEC/EIVMU architecture (FCOM) — input / sensor / output lists.

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.