FADEC Architecture — Function List, FADEC GND PWR, Overspeed Protection

FADEC gave the shape — two channels, EIVMU interface, I/O. This article gives the substance: the FADEC's full function list (what it controls, what it protects), and how it is powered, including ground power. It is the direct prelude to ENG CTL SYS FAULT.

1. FADEC functions — two classes

The FADEC system performs the following functions: Control of gas generation ‐ Control of fuel flow ‐ Acceleration and deceleration schedules ‐ Variable stator vanes, variable inlet guide vanes, and IP/HP bleed valve schedules ‐ Control of turbine clearance ‐ Idle setting. Protection against engine exceeding limits ‐ Protection against N1 and N2 overspeed (controlled by the overspeed protection unit) ‐ Turbine overspeed ‐ Monitoring of EGT during engine start on ground.

Per DSC-70-20, the FADEC's functions fall into two classes:

This is the ledger that gathers the FADEC's control objects scattered through earlier articles.

[!note]- The overspeed protection list is "N1 and N2," not N3 DSC-70-20's overspeed protection covers N1 and N2 (via the overspeed protection unit) plus turbine overspeed — N3 is not in this sentence, so it is not inferred that N3 is protected by the same unit. (The N3 red line is 100 % from LIM-ENG, see 10 — a red-line value, a separate matter from the protection-unit list.) Also note the 04 FMU overspeed protection (close HP shut-off, cut fuel) is a different statement layer; the two are reconciled in 30.

2. The EIVMU / EIU interface

The EIVMU/EIU forwards aircraft-side data to the FADEC (see 02 and the architecture diagram). The expansion of "VM" in EIVMU is not given in this description section, so it is not inferred here; the vibration parameters appear on the ENG SD (VIB N1/N2/N3, 10), and the name is resolved from AMM-77 in Engine Vibration.

3. FADEC power — normal and ground

Normal power (DSC-70-20): the aircraft network or the FADEC magnetic alternator — self-powering once the engine turns. On the ground, with the engine not running, FADEC GND PWR is used:

ENG FADEC GND PWR pb — Off : The electrical network of the aircraft or the FADEC alternator automatically supplies the FADEC. ON : On ground, when pressed the electrical network of the aircraft supplies the FADEC for 5 min, when: ‐ The ENG FIRE pb-sw is not pressed ‐ The FADEC alternator does not supply the FADEC. The ON light comes on 2 s after the ENG FADEC GND PWR pb is pushed.

Per DSC-70-90-30, pressing ENG FADEC GND PWR on the ground supplies the FADEC from the aircraft network for 5 minutes, provided the ENG FIRE pb is not pressed and the alternator is not already supplying; the ON light comes on 2 s after the push.

[!note]- What FADEC GND PWR is for (integrative synthesis) With the engine stopped the alternator does not generate, so ground maintenance/BITE needs the aircraft network to feed the FADEC — a 5-minute window. The conditions (ENG FIRE not pressed; alternator not supplying) read the verbatim. It is a maintenance-test window, not continuous power.

4. Channels A and B

The FADEC's two channels run one active, one standby, with automatic takeover (DSC-70-20, 02). The ECAM presentation of a channel fault (ENG CTL SYS FAULT) is opened in 17.

5. Counterintuitive points

[!warning]- The overspeed protection sentence says "N1 and N2," not N3 DSC-70-20 lists overspeed protection for N1/N2 (overspeed protection unit) + turbine overspeed, not N3 — not inferred here. (N3's red line is the separate 100 % from LIM-ENG, 10.)

[!warning]- FADEC GND PWR is a 5-minute window, and not with ENG FIRE pressed Ground power is 5 minutes and only with the ENG FIRE not pressed (DSC-70-90-30) — a maintenance-test window, not continuous power.

Self-test

[!note]- Q1. The FADEC's two function classes? Gas-generation control (fuel flow / accel-decel schedules / VSV·VIGV·IP-HP bleed / turbine clearance / idle) and protection against exceeding limits (N1·N2 overspeed / turbine overspeed / ground-start EGT monitoring).

[!note]- Q2. What controls N1/N2 overspeed protection? The overspeed protection unit.

[!note]- Q3. How is the FADEC normally powered, and on the ground stopped? Aircraft network or the FADEC magnetic alternator (self-powering once turning); on the ground stopped, ENG FADEC GND PWR (aircraft network for 5 min).

[!note]- Q4. Conditions and duration for FADEC GND PWR ON? On the ground, ENG FIRE not pressed + alternator not supplying, for 5 min; ON light 2 s after the push.

[!note]- Q5. Does the FADEC overspeed protection cover N3? DSC-70-20's overspeed protection lists N1 and N2 + turbine overspeed only — N3 is not in that sentence, so not inferred (its red line, 100 %, is from LIM-ENG).

Key takeaways

References

• FCOM DSC-70-20 — FADEC functions: gas-generation control list + protection (N1/N2 overspeed via overspeed protection unit, turbine overspeed, ground-start EGT monitoring).
• FCOM DSC-70-90-30 — ENG FADEC GND PWR: ground 5-min supply (ENG FIRE not pressed + alternator not supplying), ON light 2 s.
• FCOM LIM-ENG — N3 red line 100 % (see 10).

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.