A320 Architecture
Flight Control Law & Redundancy Analysis

A320 Fly-By-Wire Redundancy Explorer

Simulate multi-lane computer and hydraulic outages to observe real-time flight control reconfiguration, degradation pathways, and surface authority changes.

Open Comparison Tool
A320 Fly-By-Wire Computer and Surface Hierarchy Visual schematic showing inputs routing from Sidestick through ELAC, SEC, and FAC computers to hydraulic servos on the elevator, aileron, spoiler, and rudder. PILOT INPUT Sidestick & Pedals ELAC 1 & 2 Elevator & Aileron SEC 1, 2, 3 Spoiler & Elevator FAC 1 & 2 Yaw & Rudder Travel HYDRAULIC LOOPS GREEN (G) BLUE (B) YELLOW (Y) Elevators & THS Ailerons & Roll Spoilers Rudder & Yaw Trim
Interactive Reconfiguration Engine

Before vs. After Degradation Model

Baseline Nominal Condition

Full Fly-By-Wire flight envelope protection (Normal Law), autotrim active, full roll rate and structural limiting.

Evaluated Degradation State

Live computed law, active fallback pathways, and surviving aerodynamic surface authority.

Toggle Individual Hardware Channels
Normal Law Active

Normal Law

All flight control computers and all 3 hydraulic circuits are active. Full flight envelope protection, load alleviation, and automatic trim operate nominally.

  • Pitch: G-load command with autotrim and high/low angle of attack protection.
  • Roll: Rate command with bank angle limiting (67° max).
  • Yaw: Automatic Dutch roll damping and coordinated turn assistance.

System Availability Index

Computing Channels 7 / 7 Online
Hydraulic Pressure Circuits 3 / 3 Nominal
Fail-Operational Logic: Reconfiguration occurs automatically within milliseconds upon loss of cross-comparison validity.

Surface Actuator Authority

Nominal Degraded/Fallback Inoperative
ELAC Elevator & Aileron Computer
SEC Spoiler & Elevator Computer
FAC Flight Augmentation Computer
Green, Blue, Yellow Hydraulic Networks
Normal Law Protection Envelope
Alternate Law With Reduced Protections
Direct Law Surface Direct Proportionality
Mechanical Backup Pitch Trim & Rudder
ELAC Elevator & Aileron Computer
SEC Spoiler & Elevator Computer
FAC Flight Augmentation Computer
Green, Blue, Yellow Hydraulic Networks
Normal Law Protection Envelope
Alternate Law With Reduced Protections
Direct Law Surface Direct Proportionality
Mechanical Backup Pitch Trim & Rudder
Degradation Hierarchy

How Control Reconfiguration Occurs

The Fly-By-Wire system is engineered to protect structural integrity while preserving pilot control across sequential hardware losses.

When both ELACs fail, or when two hydraulic circuits lose nominal pressure, the system automatically transitions from Normal Law to Alternate Law. In Alternate Law, load factor demand is maintained in pitch, but high-angle-of-attack alpha protection and high-speed protection revert to stability warnings.

Operational Guidance & Pilot Reference

Flight Crew Training & Scenario Feedback

Architectural Physicality

Triple-Redundant Hydraulic Integration

Unlike pure mechanical linkages, each flight surface is powered by two or three independent hydraulic actuators receiving electrical command signals from discrete computer buses.

The system avoids common-mode failures by utilizing dissimilar microprocessors and distinct software code across the ELAC (Thomson-CSF) and SEC (SFENA) architectures.

Cockpit avionics and flight deck fly-by-wire controls
Training & Academic Scope

Explore Safely. Operate by the Book.

This interactive explorer is a simplified, non-authoritative educational model derived from public technical documentation. It omits specific sensor bus arbitration, airspeed schedule transitions, and certified flight manual revisions. It is not approved for flight crew certification or operational dispatch.

System State Reset

Return all modeled flight computers and hydraulic circuits to baseline operational configuration.

Seven computers, three hydraulics: how the A320's fly-by-wire degrades

A one-minute painted explainer of what this explorer computes when you switch off the A320's flight control computers and hydraulic circuits, followed by the real-world background and where to read more.

Read the narration

An Airbus A320 has no cables from the pilot's sidestick to the wings. Every input becomes a signal, read by flight control computers. This explorer lets you break them, one at a time. By default everything is healthy: seven of seven computers online, two ELACs, three SECs and two FACs, plus all three hydraulic circuits, green, blue and yellow. That's Normal Law, with full envelope protection. Switch off both ELACs and the tool drops to Alternate Law. Five computers remain, the spoiler and elevator computers take over pitch, and the protections become warnings. Lose two of the three SECs as well, and only three computers are left. Now it's Direct Law: stick movement maps straight to surface movement, with no protections and manual trim. Switch off all seven and you reach mechanical backup: the trim wheel moves the tail's stabilizer, and the rudder pedals steer. Hydraulics count too: lose green and yellow, and one circuit means Alternate Law. Real Airbus logic has many more triggers than this simplified model. Try a preset, then flip single channels, and watch where the law changes.

What the explorer models, and what the real aircraft does

Seven computers, two kinds

The A320 flies with two ELACs (elevator and aileron computers), three SECs (spoiler and elevator computers) and two FACs (flight augmentation computers, for the rudder and yaw damping). ELACs and SECs use different processors and separately developed software, so a single design error is unlikely to take out both.

The explorer's rule of thumb

The tool counts what is still working: no ELACs gives Alternate Law; no ELACs and at most one SEC gives Direct Law; no computers at all gives Mechanical Backup; one hydraulic circuit or four or fewer computers also gives Alternate Law. The real aircraft's reconfiguration logic depends on many more conditions, such as sensor agreement and landing gear position.

Three hydraulic circuits

Green, blue and yellow are independent 3,000 psi systems. Each primary surface is powered by at least two of them, so losing one circuit costs very little and losing two still leaves the aircraft controllable.

Protections versus warnings

In Normal Law the computers stop the aircraft exceeding limits such as a 67 degree bank or the stall angle. In Alternate Law most of those protections are lost and replaced by warnings, and in Direct Law the stick simply moves the surfaces in proportion.

Mechanical backup

If all the computers are lost, cables still connect the pitch trim wheel to the trimmable horizontal stabilizer and the rudder pedals to the rudder, which is meant to keep the aircraft stable while the crew restores the computers.

Try it in the tool

  1. Pick Dual ELAC Failure (Alternate Law) in Predefined Scenario and note the computing channels drop to 5 / 7 Online.
  2. From that state, untick SEC 1 and SEC 2 under Toggle Individual Hardware Channels and watch the result card switch to Direct Law.
  3. Choose Complete Computer Loss (Direct/Backup), then Green & Yellow Hydraulic Failure, and compare the Surface Actuator Authority map for each.

Sources and further reading

  1. Airbus A320 family · Wikipedia

    Background on the A320 as the first airliner with digital fly-by-wire and sidesticks.

  2. Flight control modes · Wikipedia

    Overview of Airbus Normal, Alternate and Direct laws and mechanical backup.

  3. Fly-by-wire · Wikipedia

    How electrical signalling replaces mechanical linkages, and why redundancy is needed.

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

    Primary engineering 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.

The video narrates this explorer's simplified, non-authoritative model; real A320 reconfiguration logic has many more conditions and is defined by Airbus documentation, not by this tool.

A320 Reconfiguration Diagnosis Report


    

      
      
    

  

  
  
  

  


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