A320 ELACs Explained: The Two Computers That Fly the Airplane

What do the ELACs do on the A320?

The 𝗘𝗟𝗔𝗖𝘀 (Elevator Aileron Computers) are the primary flight-control computers for normal pitch and normal roll. In normal law, the ELACs control both elevators, the trimmable horizontal stabilizer (𝗧𝗛𝗦), and the ailerons. They also compute yaw orders for turn coordination and yaw damping, which they transmit to the FACs.

The ELACs do not control spoilers - those are run by the SECs. The ELACs do not control the rudder pedals - those remain mechanical.

What is the difference between ELAC1 and ELAC2 on the A320?

𝗘𝗟𝗔𝗖𝟭 and 𝗘𝗟𝗔𝗖𝟮 split the primary flight-control job. Each is also the backup for the other.

The roles are split by design - the architecture is not redundant in a one-for-one sense, it is divided.

Why is ELAC2 the pitch master on the A320?

𝗘𝗟𝗔𝗖𝟮 is the normal pitch master because the FCOM defines it that way. The naming convention is counterintuitive - many candidates assume ELAC1 must be the pitch master because "1 sounds primary." It is not.

ELAC2 controls both elevators in normal operation: the left elevator via the green hydraulic jack, the right elevator via the yellow hydraulic jack. The THS is normally driven by electric motor No.1. If ELAC2 fails, pitch transfers to ELAC1, which uses the blue hydraulic jacks for the elevators and electric motor No.2 for the THS.

The single most-missed fact in A320 system orals is the 𝗘𝗟𝗔𝗖𝟮-𝗮𝘀-𝗽𝗶𝘁𝗰𝗵-𝗺𝗮𝘀𝘁𝗲𝗿 assignment.

Which hydraulic systems and electric motors do the ELACs use on the A320?

The deliberate spread across green, yellow, and blue hydraulic systems is what allows the ELACs to keep flying through partial hydraulic failures.

What happens if ELAC1 fails on the A320?

If ELAC1 fails, aileron control transfers automatically to ELAC2, which now handles both pitch and roll. The transfer is automatic and normal law is retained, but redundancy is reduced and 𝗖𝗔𝗧 𝟯 𝗗𝗨𝗔𝗟 is lost.

The ECAM alert depends on the failure mode: a full ELAC failure gives 𝗙/𝗖𝗧𝗟 𝗘𝗟𝗔𝗖 𝟭(𝟮) 𝗙𝗔𝗨𝗟𝗧; a pitch-channel-only failure gives 𝗙/𝗖𝗧𝗟 𝗘𝗟𝗔𝗖 𝟭(𝟮) 𝗣𝗜𝗧𝗖𝗛 𝗙𝗔𝗨𝗟𝗧. The operational consequence is 𝗖𝗔𝗧 𝟯 𝗦𝗜𝗡𝗚𝗟𝗘 𝗢𝗡𝗟𝗬. The airplane continues to fly in normal law with reduced redundancy.

What happens if ELAC2 fails on the A320?

If ELAC2 fails, pitch control transfers automatically to ELAC1, which now handles both pitch and roll. The elevators are now driven by the blue hydraulic jacks instead of green and yellow, and the THS is driven by electric motor No.2 instead of motor No.1.

The transfer is automatic and normal law is retained, but redundancy is reduced and 𝗖𝗔𝗧 𝟯 𝗗𝗨𝗔𝗟 is lost. The ECAM alert depends on the failure mode: a full ELAC failure gives 𝗙/𝗖𝗧𝗟 𝗘𝗟𝗔𝗖 𝟭(𝟮) 𝗙𝗔𝗨𝗟𝗧; a pitch-channel-only failure gives 𝗙/𝗖𝗧𝗟 𝗘𝗟𝗔𝗖 𝟭(𝟮) 𝗣𝗜𝗧𝗖𝗛 𝗙𝗔𝗨𝗟𝗧. The operational consequence is 𝗖𝗔𝗧 𝟯 𝗦𝗜𝗡𝗚𝗟𝗘 𝗢𝗡𝗟𝗬.

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):

Saying "both ELACs failed, so we are in alternate law" is true but incomplete - an examiner expects the full consequence set.

If both ELACs fail, can you still roll the A320?

Yes. A dual ELAC failure does not mean "no roll at all." After both ELACs fail, both ailerons are lost and the ailerons revert to damping mode. Roll remains available through the 𝘀𝗽𝗼𝗶𝗹𝗲𝗿-𝗯𝗮𝘀𝗲𝗱 𝗽𝗮𝘁𝗵.

In normal law, sidestick roll commands combine ailerons, spoilers (except spoiler No.1), and rudder for turn coordination. After both ELACs fail, the load alleviation function degrades and uses spoilers only.

Candidates who answer "both ELACs failed so we have no roll" miss the spoiler-based path entirely.

What backs up the ELACs if both fail on the A320?

If both ELACs fail, the 𝗦𝗘𝗖𝘀 become the backup path for pitch. Specifically, SEC1 and SEC2 provide the standby pitch path - they take over elevator control through the SEC standby elevator function. The THS is driven by electric motor No.2 or No.3, depending on which circuits survive.

The SECs are not a full replacement for the ELACs. The SEC backup keeps the airplane flyable; it does not restore normal law.

What is the Load Alleviation Function on the A320, and how does it change after a dual ELAC failure?

The 𝗟𝗼𝗮𝗱 𝗔𝗹𝗹𝗲𝘃𝗶𝗮𝘁𝗶𝗼𝗻 𝗙𝘂𝗻𝗰𝘁𝗶𝗼𝗻 (𝗟𝗔𝗙) is an automatic protection that reduces wing structural loads by deflecting flight-control surfaces upward in symmetric pairs. In normal operation, LAF uses both ailerons and spoilers.

After both ELACs fail, LAF is degraded and uses 𝘀𝗽𝗼𝗶𝗹𝗲𝗿𝘀 𝗼𝗻𝗹𝘆. This is a documented consequence on the F/CTL ELAC 1(2) FAULT (BOTH COMPUTERS FAILED) ECAM. Separately, the ECAM status requires 𝗙𝗟𝗔𝗣 𝗟𝗩𝗥 𝟯, 𝗔𝗣𝗣𝗥 𝗦𝗣𝗗 𝗩𝗥𝗘𝗙 + 𝟭𝟬 𝗞𝗧, and 𝗟𝗗𝗚 𝗗𝗜𝗦𝗧 𝗣𝗥𝗢𝗖 𝗔𝗣𝗣𝗟𝗬.