A320 Flight Control Computers: ELAC, SEC, FAC - The Foundation Guide

What computers fly the Airbus A320?

The A320 is flown by seven flight-control computers.

Two additional computers, the 𝗙𝗖𝗗𝗖𝘀 (Flight Control Data Concentrators), collect data from the ELACs and SECs and send it to the displays and the maintenance system. The FCDCs do not fly the aircraft.

What does the ELAC do on the A320?

The 𝗘𝗟𝗔𝗖𝘀 (Elevator Aileron Computers) control the elevator, the trimmable horizontal stabilizer (𝗧𝗛𝗦), and the ailerons in normal law. 𝗘𝗟𝗔𝗖𝟮 is the primary pitch computer. 𝗘𝗟𝗔𝗖𝟭 is the primary roll and aileron computer. If one ELAC fails, the other takes over its function with a hydraulic and electric motor reshuffle.

What does the SEC do on the A320?

The 𝗦𝗘𝗖𝘀 (Spoiler Elevator Computers) control the spoilers for roll control, speedbrake, and ground-spoiler operation. They also provide a standby pitch path that takes over if both ELACs fail.

What does the FAC do on the A320?

The 𝗙𝗔𝗖𝘀 (Flight Augmentation Computers) handle yaw damping, turn coordination, rudder trim, and rudder travel limiting. They also compute the characteristic speeds on the PFD, the alpha-floor function, the low-energy aural warning, and windshear detection.

The FACs do not create the rudder control path. They augment it. The rudder is controlled by the pilot through a mechanical path and is hydraulically actuated by three servojacks.

Which ELAC is the pitch master on the A320?

𝗘𝗟𝗔𝗖𝟮 is the pitch master in normal law. 𝗘𝗟𝗔𝗖𝟭 is the roll and aileron master. This is the single most-missed fact in A320 system orals. The names mislead: the computer called "2" flies pitch, and the computer called "1" flies roll.

If 𝗘𝗟𝗔𝗖𝟮 fails, pitch transfers to 𝗘𝗟𝗔𝗖𝟭, using the blue hydraulic jacks for the elevators and electric motor No.2 for the THS.

What happens if both ELACs fail on the A320?

If both ELACs fail, the airplane loses pitch and roll normal laws. Verified ECAM consequences for 𝗙/𝗖𝗧𝗟 𝗘𝗟𝗔𝗖 𝟭(𝟮) 𝗙𝗔𝗨𝗟𝗧 (BOTH COMPUTERS FAILED):

What happens if all three SECs fail on the A320?

If all three SECs fail, all SEC-controlled roll spoilers are lost. The verified consequences are 𝗿𝗼𝗹𝗹 𝗱𝗶𝗿𝗲𝗰𝘁 𝗹𝗮𝘄 and 𝗽𝗶𝘁𝗰𝗵 𝗮𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗹𝗮𝘄. The direct-law activation status at landing is 𝗔𝗣-𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁:

Operational consequences: major roll degradation, Flap 3 / 𝗩𝗥𝗘𝗙+𝟭𝟬 / landing-distance procedure, and 𝗖𝗔𝗧 𝟯 𝗦𝗜𝗡𝗚𝗟𝗘 only. An oral answer of "direct law at gear down" without the AP-dependent split is too blunt - an examiner will press on it.

What happens if both FACs fail on the A320?

If both FACs fail, the aircraft loses yaw damper, rudder trim, rudder travel limit, PFD characteristic speeds, and windshear detection. Flight control law degrades to 𝗙/𝗖𝗧𝗟 𝗔𝗟𝗧𝗡 𝗟𝗔𝗪 (𝗣𝗥𝗢𝗧 𝗟𝗢𝗦𝗧), and reverts to 𝗗𝗜𝗥𝗘𝗖𝗧 𝗟𝗔𝗪 when landing gear is selected down.

The 𝗿𝘂𝗱𝗱𝗲𝗿 𝘁𝗿𝗮𝘃𝗲𝗹 𝗹𝗶𝗺𝗶𝘁𝗲𝗿 may be frozen at an inappropriate position at failure time, which is why 𝗥𝗨𝗗 𝗪𝗜𝗧𝗛 𝗖𝗔𝗥𝗘 is not just a caution - it is a structural warning.

Is the rudder on the A320 mechanical?

The pilot controls the rudder through a mechanical path from the rudder pedals, but the rudder itself is hydraulically actuated by three servojacks. The 𝗙𝗔𝗖𝘀 do not fly the rudder - they augment it with yaw damping, turn coordination, rudder trim, and rudder travel limitation.

The mechanical pedal-to-rudder linkage is a deliberate design feature that preserves yaw control through certain failure scenarios. Understanding this distinction - mechanical path, hydraulic actuation, FAC augmentation - is the clean answer an examiner is looking for.

What is the difference between an ELAC and a SEC on the A320?

The 𝗘𝗟𝗔𝗖𝘀 are the primary computers for normal pitch and roll control - they run the elevator, the THS, and the ailerons. The 𝗦𝗘𝗖𝘀 are primary for spoiler control and serve as a backup pitch path if both ELACs fail. SECs do not control ailerons.

The architecture is layered: 𝗘𝗟𝗔𝗖𝘀 𝗳𝗶𝗿𝘀𝘁, 𝗦𝗘𝗖𝘀 𝗮𝘀 𝗯𝗮𝗰𝗸𝘂𝗽 for pitch, and a fixed spoiler-to-SEC map for roll-control spoilers. The two names describe two different jobs, not two levels of the same job.