FBW-A320

Airbus A320 Flight Control Redundancy & Law Simulator

FLIGHT CONTROL LAW: ALTERNATE LAW 2
PRESETS:
Flight Control Computers (ELAC / SEC / FAC) & Hydraulics Click to toggle fault/pressurization
ECAM Status & Reconfiguration Assessment ELEV: SEC1/SEC2 | ROLL: AIL+SPOIL
ELAC 1 & 2 offline triggers automatic reconfiguration to Alternate Law 2 without pitch/bank envelope protection; pitch elevator command transfers seamlessly to SEC 1 & 2, while roll transitions to ailerons and roll spoilers with direct stick proportionality.
Flight Envelope Protections AIRBUS 320 SPECS
Protection Feature Status Mode
Control Surface Deflection Telemetry LIVE ANGLES
Left Elevator
0.0°
Right Elevator
0.0°
Left Aileron
0.0°
Right Aileron
0.0°
Rudder Yaw
0.0°
THS Pitch Trim
0.0°
Side-Stick Dynamic Control Test DRAG / TOUCH
PITCH DEMAND (Y) / ROLL DEMAND (X)
Stick X: +0.60 Stick Y: -0.45

When both ELACs fail: what the A320 sidestick still moves

A one-minute painted explainer of this simulator's default dual-ELAC scenario: which flight law it picks, which protections it drops, and how far each control surface moves for the same sidestick input.

Read the narration

When an A320 pilot moves the sidestick, computers decide how far each control surface moves. This simulator opens on a bad day: both elevator and aileron computers, the ELACs, have failed. The tool drops to Alternate Law two. Pitch control passes to spoiler and elevator computers one and two, and the protections against stall, over-banking and extreme pitch are lost. A stall warning takes their place. The stick is held back and to the right. Pulling back forty-five percent commands the elevators thirteen and a half degrees, trailing edge up, and the stabilizer trim moves about two degrees. But look at the ailerons: zero. In this model they need a working ELAC. On the real aircraft, roll then comes from the spoilers. The rudder, still served by its augmentation computers, adds about seven degrees. Press Normal Law and the same stick input swings the ailerons fifteen degrees each way, and every protection comes back. It's a simplified teaching model, not a flight manual. Drag the stick, toggle single computers, and watch which surfaces still answer.

What the simulator computes, and what the real A320 does

The simulator's surface rule

Elevators move 30 degrees per full pull and 17 per full push while any ELAC or SEC 1/2 and any hydraulic circuit works; ailerons move 25 degrees per full roll input only while an ELAC and the green or blue circuit work; the rudder moves 12 degrees per full roll input while a FAC works. These are the tool's assumptions, not certified gains.

Why ailerons need an ELAC

On the A320 the ailerons are controlled only by the two ELACs. If both fail, the ailerons go to a damping mode and roll is controlled by the spoilers, which the SECs command.

Alternate Law trades protection for warnings

In Normal Law the computers stop the aircraft exceeding the stall angle, a 67 degree bank and pitch limits of about 30 degrees up and 15 down. In Alternate Law those protections are lost; the crew instead gets stall and overspeed warnings, and the ECAM shows a reduced maximum speed of 320 knots or Mach 0.77.

Dissimilar redundancy

The A320 has seven flight control computers: two ELACs, three SECs and two FACs. ELACs and SECs use different processors and separately developed software, so one design error is unlikely to disable both families at once.

Model limits

Some presets differ from published Airbus logic; for example, the tool shows Direct Law after a green plus yellow hydraulic loss, while Airbus procedures describe Alternate Law for that failure. Use the tool for intuition about redundancy, not for procedures.

Try it in the tool

  1. Start on the Air India Dual ELAC Dropout preset and read the Control Surface Deflection Telemetry: elevators -13.5°, ailerons 0.0°.
  2. Click Normal Law (Nominal) without moving the stick and watch the Left and Right Aileron values jump to ±15.0° while the Flight Envelope Protections table turns active.
  3. Drag the Side-Stick Dynamic Control Test pad, then click individual units such as ELAC 1 or FAC 1 in the rack to see which surfaces stop responding.

Sources and further reading

  1. Flight control modes · Wikipedia

    Airbus Normal, Alternate and Direct laws and the protections each keeps or loses.

  2. Airbus A320 family · Wikipedia

    Background on the A320's digital fly-by-wire and sidestick controls.

  3. Side-stick · Wikipedia

    How the sidestick replaces the control column in fly-by-wire airliners.

  4. AIRBUS A320/A330/A340 electrical flight controls: a family of fault-tolerant systems · D. Briere and P. Traverse, FTCS-23, IEEE, 1993

    Primary description of the ELAC/SEC/FAC architecture and its dissimilar redundancy.

  5. 14 CFR 25.671 Control systems: general · U.S. eCFR

    Certification rule requiring continued safe flight after flight control system failures.

Angles in the video come from this simulator's simplified model and its default stick position; they illustrate the redundancy logic and are not certified A320 control gains or procedures.

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