Demystifying Airbus A320 Flight Control Computers: ELAC, SEC, and FAC

Demystifying Airbus A320 Flight Control Computers: ELAC, SEC, and FAC

For pilots transitioning from conventional control-column aircraft to the FBW (Fly-By-Wire) side-stick mechanics of the Airbus A320, the complex interaction of the flight control computers can feel like a computer science syllabus.

During recurrent simulator checks or a line transition course, examiners often test your absolute understanding of: What happens to the flight controls if a specific computer defaults?

In this post, we break down the operational duties, physical outputs, and backup architectures of the classic A320 flight control triad: ELAC, SEC, and FAC.

Meet the A320 Flight Control Triad

The A320 fly-by-wire system uses seven computers: 2 ELACs (Elevator Aileron Computers) controlling pitch and roll, 3 SECs (Spoiler Elevator Computers) handling spoilers and backup pitch, and 2 FACs (Flight Augmentation Computers) managing the yaw axis, rudder limiting, and flight envelope speed calculations.

The system is commanded via 7 digital fly-by-wire flight control computers:

• 2x ELACs: Elevator Aileron Computers (primary pitch and roll commands)
• 3x SECs: Spoiler Elevator Computers (primary spoilers control and backup pitch axes commands)
• 2x FACs: Flight Augmentation Computers (yaw damping, turn coordination, envelope speeds calculations, and windshear detection)

1. ELAC (Elevator Aileron Computer) - 2 Installed

The ELAC is the primary pitch and roll computer on the A320. It commands both elevators, the Trimmable Horizontal Stabilizer (THS), and the ailerons. If ELAC 1 fails, ELAC 2 takes over. If both fail, SEC 1 and SEC 2 automatically assume elevator and THS control.

As the name implies, the two ELAC units are directly in charge of pitch (moving the elevator and tail stabilizer) and roll (moving the ailerons).

Primary Functions:

• Normal, Alternate, and Direct pitch laws command execution.
• Aileron command and active dampening control.
• Active elevator control (both left and right elevators are commanded independently).
• Automatic Pitch Trim (via the THS motor).

If ELAC 1 Fails:

Control of the elevators and THS automatically transfers over to ELAC 2.

If BOTH ELACs Fail:

Automatic control of the pitch axes and active backup roll transfers gracefully to the SEC computers. Your sidestick commands will remain active, but the system may degrade from Normal Law down to Alternate Law, depending on the severity of of secondary utility failures.

2. SEC (Spoiler Elevator Computer) - 3 Installed

SECs primarily control all spoiler surfaces for roll augmentation, speed braking, and automatic ground spoiler deployment. SEC 1 and SEC 2 additionally contain backup elevator circuits that activate if both ELACs fail. SEC 3 handles spoilers only and has no pitch-control output.

The three SEC computers are primarily designed to handle spoiler surfaces, but they also host elevator control cards as a built-in safety fallback.

Primary Functions:

• Spoiler Control: All spoiler panels are commanded by SECs. They handle roll augmentation, speed brakes, ground spoilers (automatic deployment on touchdown), and active load alleviation.
• Backup Pitch Control: SEC 1 and SEC 2 contain independent backup elevator control circuits. If both ELAC 1 and ELAC 2 go offline, SEC 1 / SEC 2 step in immediately to command the elevator servos and the THS trim. Note that SEC 3 is reserved strictly for spoiler inputs and has no pitch-control outputs.

3. FAC (Flight Augmentation Computer) - 2 Installed

FACs control the rudder for yaw damping, turn coordination, and rudder travel limiting at cruise speeds. They also calculate the flight envelope speeds displayed on the PFD — VLS, Green Dot, Alpha Prot, and Alpha Max — and issue the WINDSHEAR warning if headwind gradient changes are detected.

The two FAC computers stand apart. Instead of directly controlling pitch/roll surfaces, they manage the Yaw axis (Rudder) and calculate active flight envelope speeds (the minimum and maximum safe speeds shown on your Primary Flight Display).

Primary Functions:

• Yaw Control: Turn coordination, yaw damping, rudder travel limiting (preventing aggressive full rudder deflection at high cruise speeds), and automatic rudder trim.
• Flight Envelope Calculations: The FAC calculated values for:
• - VLS (Lowest Selectable Speed).
• - Green Dot Speed (Best lift-to-drag glide ratio).
• - Alpha Prot (Angle of Attack protection boundary).
• - Alpha Max (Maximum permissible angle of attack).
• Wind Shear Detection: Evaluates changes in headwind gradients to issue the red audio "WINDSHEAR" warning on the flight deck.

How to Memorize the Triad for Your Technical Exam

The fastest revision method is a simple three-row table: ELAC → Elevators + THS + Ailerons; SEC → Spoilers (SEC 1 & 2 also backup elevators); FAC → Rudder + PFD Speed Tape + Windshear. Drilling this table under timed conditions replicates the recall pressure of a real type-rating systems paper.

To pass your recurrent system simulator review with ease, memorize this simple quick-table of primary outputs:

Master Systems with the Heading380 Spaced Repetition Platform

Heading380's A320 systems preparation combines an Analytics Sunburst to pinpoint weak ATA chapters, daily FCOM-based question banks with Gemini-integrated explanations, and a full timed A320 FCOM mock exam with sim-check pressure to consolidate systems knowledge before live simulator entries.

System failures are complex to master under stress. Heading380's modern desktop learning modules make systems preparation effortless:

1. Interactive Sunburst Inspection: Head to Analytics, where you can visualize the systems breakdown on our custom sunburst chart. Is ATA 27 (Flight Controls) in orange or green? If orange, you have a weak error logging habit in simulated control failures.

2. Daily Practice Questions: Generate new system failure scenarios in the Syllabus Modules using our Gemini-integrated pilot coach.

3. Run A320 Type Simulators: Go to Mock Exams, run the "Airbus A320 FCOM Technical Systems 1400Q Paper", and master all limitations, computer transfer behaviors, and abnormal checklist items before stepping into your next sim check.