Control Inputs and Power Supply — Sidesticks, the Sensor Suite, and the Battery-Backed Computers

The computers do not only read the sidesticks. They read a whole sensor suite — pedals, accelerometers, a yaw-rate gyro, throttle position, hydraulic pressure — and several of those sensors are the EFCS's own backups for an ADIRU loss. This article covers what feeds the flight control computers, and how the key computers stay powered on the battery.

The electrical control orders and certain feedbacks are sent to the flight control computers by specific control components and transducer units: the Captain and First Officer side sticks... the transducer units (rudder pedals, rudder, elevators)... accelerometers (Nz)... accelerometers (Ny)... the rate gyro unit (yaw rate)... the throttle control units... the pressure switches (hydraulic systems)... the Power Supply Decoupling Units (PSDU). — AMM 27-92-00

1. The sidesticks — order signals plus artificial feel

Per AMM 27-92-00, the Captain and FO sidesticks transmit lateral and longitudinal orders to FCPC 1/2/3 and FCSC 1/2 as electrical signals, and generate the artificial feel loads. In autopilot mode the stick is held at neutral with a higher load — to prevent unwanted reversion to manual control, while still allowing the pilot to override the AP.

[!warning]- The sidestick is built so one failure cannot disarm an axis Per AMM 27-92-00, the design ensures that the rupture or disconnection of any single part cannot lose all the artificial-feel loads on one axis, nor free more than one of the four potentiometer groups per axis. Each axis is read by four potentiometer groups, so the order signal is heavily voted — a single break degrades but does not blind the axis. The hand grip carries the PTT and the takeover/priority pushbutton (16), plus a neutral-locking mechanism used in AP mode.

2. The sensor suite — and the ADIRU backups

Per AMM 27-92-00, the computers also receive:

[!warning]- The EFCS carries its own accelerometers and gyro as an ADIRU backup (integrative synthesis) This is the headline: the flight control system does not depend solely on the ADIRS for the motion data its laws need. It has dedicated Nz/Ny accelerometers and a yaw-rate gyro so that with both (or all three) ADIRUs lost, the FCPCs can still consolidate load factor and compute the Dutch-roll/turbulence-damping laws (AMM 27-92-00). The protected laws lean on the ADIRUs, but the basic damping and load-factor sensing survive their loss — a deliberate independent fallback.

[!note]- Throttle position is a flight-control input, and hydraulic switches drive reconfiguration (integrative synthesis) Two non-obvious feeds: the throttle lever position goes to the FCPCs for ground-spoiler logic (23) — the spoilers know where the thrust levers are. And the hydraulic pressure switches tell FCPC1/FCSC1 which systems are pressurised — this is exactly the sensing behind the reconfiguration chains (e.g. green lost → P2 master). FCPC2/3 and FCSC2 get the same hydraulic status from the ATA-29 switches.

3. Computer engagement and reset

Per AMM 27-92-00, each FCPC/FCSC has a guarded engagement pushbutton: pressed in = engaged (OFF and FAULT legends off); FAULT legend = failure; released out = OFF → the computer's output relays de-energise, the digital section resets, discrete outputs go open-circuit, and the system buses no longer refresh its data. This is the crew's means of resetting a faulted computer.

4. Power supply — the battery-backed pair

The diode unit permits decoupling of the FCPC1 and FCSC1 normal and battery power supplies. Decoupling is achieved via two power diodes D1 and D2. Diodes P1, P2, P3 are used for lightning strike protection.

Per AMM 27-92-00, the PSDU (13CE, 17CE) decouple the normal and battery power supplies of FCPC1 and FCSC1.

[!warning]- FCPC1 and FCSC1 are the battery-backed survivors (integrative synthesis) Of the six computers, FCPC1 and FCSC1 have their normal/battery supplies decoupled by the PSDU (AMM 27-92-00) — these are the computers kept alive on the battery in a deep electrical failure, which is why they sit at the bottom of the reconfiguration chains (SEC1 is the last elevator/rudder computer). The lightning-protection diodes (P1/P2/P3) guard the same supply path.

5. Counterintuitive points

[!warning]- The flight controls have their own accelerometers and gyro Nz/Ny accelerometers and a yaw-rate gyro feed the FCPCs directly, as an ADIRU-loss backup for load factor and damping laws (AMM 27-92-00) — independent of the air-data/inertial system.

[!warning]- Thrust-lever position is a flight-control signal Throttle position goes to the FCPCs for ground-spoiler control (AMM 27-92-00), not just to the engines.

Self-test

[!note]- Q1. What do the sidesticks send, and what holds them in AP mode? Lateral/longitudinal electrical order signals to FCPC1/2/3 + FCSC1/2, plus artificial feel; in AP mode held at neutral with higher load (override still possible).

[!note]- Q2. Which EFCS sensors back up an ADIRU loss? Nz accelerometers (load-factor consolidation if both ADIRUs fail), and the yaw-rate gyro (Dutch-roll damping if all 3 ADIRUs lost); Ny accelerometer for turbulence damping.

[!note]- Q3. What two roles do the hydraulic pressure switches and throttle units play? Hydraulic switches → G/B/Y pressurised status to FCPC1/FCSC1 (reconfiguration sensing); throttle units → position to FCPCs for ground-spoiler control.

[!note]- Q4. Which computers are battery-backed, and via what? FCPC1 and FCSC1, via the PSDU (decoupling normal/battery supplies).

Key takeaways

References

• AMM 27-92-00 (EFCS Control Inputs and Power Supply — Description and Operation) — Captain/FO sidesticks (lateral/longitudinal order signals to FCPC1/2/3 + FCSC1/2, artificial feel, AP neutral-hold with override, four potentiometer groups per axis, hand-grip PTT + takeover/priority pb); six transducer units (rudder pedals → FCPC1/2/3 + FCSC1; rudder/elevator position monitoring + ECAM); speedbrake control transducer (speedbrake/ground-spoiler orders to FCPC1/2/3); guarded FCPC/FCSC engagement pushbuttons (engage/fault/reset-neutralise); vertical accelerometers Nz (load-factor consolidation if both ADIRUs fail + turbulence damping); lateral accelerometer Ny (turbulence damping); rate gyro (yaw rate to FCPC1 + FCSCs, Dutch-roll damping if all 3 ADIRUs lost); throttle control units (position to ECUs + FCPC1/2/3 for ground-spoiler control); hydraulic pressure switches (G/B/Y status to FCPC1/FCSC1, ~100 bar); PSDU (decouple FCPC1/FCSC1 normal/battery supplies, lightning-protection diodes).

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.