A320 SECs and FACs Explained - Triple-SEC and Dual-FAC Failure Guide for Pilots

✈ A320 Training · AEO Foundation Series · Spoke 3 of 3

A320 SECs and FACs Explained: The Five Quiet Computers That Finish Oral Exams

Q: What do the SECs do on the A320?

The SECs (Spoiler Elevator Computers) on the A320 have two distinct jobs. First, they control specific spoiler panels for roll authority, speedbrake, and ground lift-dumping. The spoiler assignment is fixed and is not in tidy ascending order: SEC 3 controls the No. 2 spoilers, SEC 1 controls the No. 3 and No. 4 spoilers, and SEC 2 controls the No. 5 spoilers. Second, SEC 1 and SEC 2 provide the backup pitch path - they take over elevator control if both ELACs fail. SEC 3 does not participate in the pitch backup and controls only its assigned spoiler panel. The SECs also independently compute ground spoiler deployment logic from landing gear compression and wheel tachometer inputs. The SECs do not control the ailerons (those are ELAC territory in normal law), and they do not run the flight envelope protections.

Q: What do the FACs do on the A320?

The FACs (Flight Augmentation Computers) provide the electrical rudder control functions and compute the flight envelope information on the PFD. The A320 rudder has two distinct control paths. The pedal path is mechanical - the linkage from the pilot's feet to the rudder surface does not pass through any computer, and the rudder is hydraulically actuated by three servojacks. The FACs provide the electrical rudder control functions: yaw damping, turn coordination, rudder trim, and rudder travel limitation. The FACs also control the PFD speed scale and compute the dynamic characteristic speeds (VLS, VFE, VMO, VMAX, F-speed, S-speed, and green dot), the alpha-floor command logic, the windshear detection and warning, and the low-energy 'SPEED SPEED SPEED' warning. The ADIRUs provide the raw air data. On newer effectivity (MSN 06003-07077), the FCOM states the FAC computes operating speeds based on FMS gross weight, with FAC GW/CG computation available as backup.

Q: Which spoiler does each SEC control on the A320?

The spoiler-to-SEC assignment is fixed: SEC 3 controls the No. 2 spoilers, SEC 1 controls the No. 3 and No. 4 spoilers, and SEC 2 controls the No. 5 spoilers. The mapping is not symmetrical and not in ascending order. The numbering convention for the SECs does not match the numbering convention for the spoiler panels. Spoiler No. 1 is not part of normal in-flight sidestick roll control or speedbrake operation. The speedbrakes are spoilers 2, 3, and 4. The ground spoiler function involves all spoilers. A candidate who confidently states a wrong SEC-to-spoiler mapping in an oral exam loses the examiner's trust on subsequent answers, because the mapping is the kind of detail the FCOM lays out explicitly and there is no excuse for getting it wrong.

Q: What happens if one SEC fails on the A320?

A single SEC failure (F/CTL SEC 1 FAULT, SEC 2 FAULT, or SEC 3 FAULT) triggers an amber ECAM caution and a panel fault light. Flight control laws remain intact. The airplane stays in normal law with full envelope protections active. The specific spoiler panels assigned to the failed computer are lost or retracted, but the roll authority through the remaining panels and the ailerons is preserved. ECAM addresses the failure with an INOP SYS entry and a landing performance penalty applies per the QRH. For SEC 1 or SEC 2 failure specifically, the elevator backup capability is now degraded - one of the two SECs that can provide pitch backup is gone, and only the remaining one is available if both ELACs subsequently fail. The pilot does not feel this in normal operation because the ELACs are still flying the airplane.

Q: Why does SEC 1 failure restrict speedbrake on the A320?

SEC 1 controls the No. 3 and No. 4 spoilers, which are the primary speedbrake surfaces. When SEC 1 fails, the ECAM presents SPD BRK DO NOT USE as a published operational restriction. This is not a slight reduction in speedbrake authority - it is an explicit prohibition. The restriction exists because the speedbrake function relies on the symmetric deployment of the No. 3 and No. 4 panels, and the loss of SEC 1 removes that capability. A candidate quoting 'reduced speedbrake authority' rather than 'SPD BRK DO NOT USE' has the wrong mental model and an examiner will press on it. The landing performance penalty for SEC 1 failure is more substantial than for SEC 2 or SEC 3 failure because the speedbrake restriction affects the available deceleration profile on approach and landing.

Q: What happens if all three SECs fail on the A320?

A triple-SEC failure (F/CTL SEC 1+2+3 FAULT) reverts the airplane to ALTN LAW with PROT LOST. All SEC-controlled roll spoilers are lost. The direct-law reversion that follows is configuration-driven, not autopilot-state-driven. With the autopilot engaged at the time of failure, the trigger for direct law is WHEN L/G DN AND AP OFF - both landing gear extension and autopilot disengagement are required. Without the autopilot engaged, the trigger is WHEN L/G DN - landing gear extension alone produces the reversion. There is also a configuration substitution worth knowing: ELAC uses slats/flaps CONF 2 as the trigger instead of landing gear extension when the substitution logic is active. The common wrong answer in oral exams is 'direct law on AP disconnect.' That is incorrect. The trigger is tied to landing configuration, not autopilot state alone. The right answer quotes the FCOM conditions exactly and treats them as configuration-gated rather than improvising about AP timing.

Q: What happens if one FAC fails on the A320?

A single FAC failure (AUTO FLT FAC 1(2) FAULT) transfers all FAC functions to the surviving FAC. Yaw damping, turn coordination, rudder trim, rudder travel limitation, characteristic speed computation, alpha-floor command, windshear detection, and low-energy warning all continue to operate through the surviving computer. The pilot does not feel a handling change. The PFD speed scale still shows characteristic speed markers and the rudder still has its variable travel limiter. However, the status message shows BOTH PFD ON SAME FAC and the autoland capability degrades to CAT 3 SINGLE ONLY. The redundancy that allowed CAT 3 DUAL autoland is gone. Any approach to minima below CAT 3 SINGLE requires the redundancy that no longer exists, and the candidate who shrugs and continues without noticing the operational change discovers it at the worst possible moment.

Q: What happens if both FACs fail on the A320?

A dual FAC failure (AUTO FLT FAC 1+2 FAULT) produces a law outcome that is effectivity-dependent. The FCOM specifies different consequences for different MSN groups, and the article-level rule is that there is no single universal answer. For some MSN groups the cascade leads to F/CTL ALTN LAW (PROT LOST) and may show WHEN L/G DN: DIRECT LAW at gear extension. For other MSN groups, the law table states ALTN LAW is indicated with no reversion to DIRECT LAW at landing gear extension. The candidate-intuitive answer that 'dual FAC failure leaves us in normal law as long as the ELACs are healthy' is wrong for every MSN group - the FCOM specifies a law reversion in all cases. The correct oral exam answer is to know which MSN group the operator's fleet falls into and quote the exact law table for that effectivity. Lost functions common across both effectivity groups include yaw damping, turn coordination, rudder trim, characteristic speeds on the PFD, alpha-floor (inhibited because alternate law is active), windshear detection, and low-energy warning. The rudder travel limiter is locked at the value reached at the second failure, with the ECAM showing RUD WITH CARE ABV 160 KT. Full rudder travel authority is recovered at slats extension. For speed handling on the approach, follow the ECAM status: APPR SPD VREF + 10 KT and, where applicable, OPERATING SPD COMPUTE. NO DISPATCH applies under MEL.

Q: Where do A320 characteristic speeds come from?

The dynamic characteristic speeds on the PFD speed scale (VLS, VFE, VMO, VMAX, F-speed, S-speed, and green dot) are computed and displayed by the FACs. The FAC controls the PFD speed scale. The ADIRUs provide raw air data (airspeed, altitude, angle of attack, temperature). On newer effectivity (MSN 06003-07077), the FCOM states the FAC computes operating speeds based on FMS gross weight, with FAC GW/CG computation available as backup. The FAC is the processing layer that combines air data with weight and configuration information to display the characteristic speeds. A total FAC failure removes the characteristic speed overlays without affecting the underlying air data. If both FACs fail, raw airspeed remains on the PFD - the characteristic speed markers disappear, but the airspeed itself does not. The examiner trap is the candidate who answers 'the ADIRUs' alone when asked where the characteristic speeds come from. The right answer names the FAC as the computation and display layer and acknowledges the FMS gross weight relationship on newer effectivity.

Q: Is the A320 rudder mechanical or electronic?

The A320 rudder has two control paths. The pedal path is mechanical - the linkage from the pilot's feet to the rudder surface does not pass through any computer, and the rudder is hydraulically actuated by three servojacks. The FACs provide the electrical rudder control functions on top of the mechanical path: yaw damping, turn coordination, rudder trim, and rudder travel limitation. The two-path design matters operationally because dual FAC failure removes the electrical rudder control functions but does not remove the mechanical pedal authority. The pilot retains direct mechanical rudder authority with no augmentation, which is a fundamentally different situation than 'no rudder at all.' The mechanical pedal-to-rudder linkage is a deliberate design feature that preserves yaw control through certain failure scenarios that would otherwise eliminate it.

Plain answers for type rating candidates and line pilots. The three SECs, the two FACs, the spoiler map, the triple-SEC trigger trap, and the effectivity-dependent dual-FAC law reversion most candidates get wrong.

The Airbus A320 has seven flight-control computers. Two are the ELACs that get most of the architectural spotlight. The other five are the three 𝗦𝗘𝗖𝘀 (Spoiler Elevator Computers) and the two 𝗙𝗔𝗖𝘀 (Flight Augmentation Computers), and they do most of the unglamorous work that keeps the airplane controllable. The SECs run specific spoiler panels on a fixed map, handle ground lift-dumping, and provide the backup pitch path if both ELACs fail. The FACs provide the electrical rudder control functions (yaw damping, turn coordination, rudder trim, and rudder travel limitation) alongside the mechanical pedal path, and they also compute the characteristic speeds on the PFD, the alpha-floor command logic, the windshear detection, and the low-energy warning. Two specific cascades on these systems finish oral exams: the triple-SEC failure with its configuration-driven direct-law trigger, and the dual-FAC failure with its effectivity-dependent law outcome. This page answers the questions a pilot actually types into a search bar when they need to know.

The core architecture and ECAM consequences on this page are supported by the FCOM. The full architectural walkthrough, with examiner traps and citation-backed depth, lives in the A320 Oral Exam Prepper at customgptsolutions.ai. For the foundational seven-computer overview, see the Foundation guide. For the ELAC deep-dive, see the ELAC deep-dive.

Frequently Asked Questions

SEC and FAC Architecture, Failure Cascades, and Examiner Traps

What do the SECs do on the A320?

The 𝗦𝗘𝗖𝘀 (Spoiler Elevator Computers) on the A320 have two distinct jobs.

The Two Jobs of the SECs:

• Spoiler control for roll, speedbrake, ground lift-dumping • Backup pitch path if both ELACs fail (SEC 1 and SEC 2 only) • Ground spoiler logic from gear compression + wheel tachometer • SEC 3 does NOT participate in pitch backup

The spoiler assignment is fixed and is not in tidy ascending order: 𝗦𝗘𝗖 𝟯 controls the No. 2 spoilers, 𝗦𝗘𝗖 𝟭 controls the No. 3 and No. 4 spoilers, and 𝗦𝗘𝗖 𝟮 controls the No. 5 spoilers. The SECs do not control the ailerons (those are ELAC territory in normal law), and they do not run the flight envelope protections.

What do the FACs do on the A320?

The 𝗙𝗔𝗖𝘀 (Flight Augmentation Computers) provide the electrical rudder control functions and compute the flight envelope information on the PFD. The A320 rudder has two distinct control paths. The 𝗽𝗲𝗱𝗮𝗹 𝗽𝗮𝘁𝗵 𝗶𝘀 𝗺𝗲𝗰𝗵𝗮𝗻𝗶𝗰𝗮𝗹 - the linkage from the pilot's feet to the rudder surface does not pass through any computer, and the rudder is hydraulically actuated by three servojacks.

FAC Electrical Rudder Functions (on top of mechanical path):

• Yaw damping • Turn coordination • Rudder trim • Rudder travel limitation

FAC PFD & Envelope Functions:

• Dynamic characteristic speeds (VLS, VFE, VMO, VMAX, F, S, green dot) • Alpha-floor command logic • Windshear detection and warning • Low-energy "SPEED SPEED SPEED" warning

The ADIRUs provide the raw air data. On newer effectivity (𝗠𝗦𝗡 𝟬𝟲𝟬𝟬𝟯-𝟬𝟳𝟬𝟳𝟳), the FCOM states the FAC computes operating speeds based on FMS gross weight, with FAC GW/CG computation available as backup.

Which spoiler does each SEC control on the A320?

The spoiler-to-SEC assignment is 𝗳𝗶𝘅𝗲𝗱. The mapping is not symmetrical and not in ascending order. The numbering convention for the SECs does not match the numbering convention for the spoiler panels.

SEC-to-Spoiler Map (Memorize Cold):

• SEC 3 → No. 2 spoilers • SEC 1 → No. 3 and No. 4 spoilers • SEC 2 → No. 5 spoilers • Spoiler 1 → not in normal sidestick roll / speedbrake • Speedbrakes → spoilers 2, 3, and 4 • Ground spoilers → all spoilers

A candidate who confidently states a wrong SEC-to-spoiler mapping in an oral exam loses the examiner's trust on subsequent answers, because the mapping is the kind of detail the FCOM lays out explicitly and there is no excuse for getting it wrong.

What happens if one SEC fails on the A320?

A single SEC failure (𝗙/𝗖𝗧𝗟 𝗦𝗘𝗖 𝟭 𝗙𝗔𝗨𝗟𝗧, 𝗦𝗘𝗖 𝟮 𝗙𝗔𝗨𝗟𝗧, or 𝗦𝗘𝗖 𝟯 𝗙𝗔𝗨𝗟𝗧) triggers an amber ECAM caution and a panel fault light. Flight control laws remain intact. The airplane stays in normal law with full envelope protections active. The specific spoiler panels assigned to the failed computer are lost or retracted, but the roll authority through the remaining panels and the ailerons is preserved.

ECAM addresses the failure with an 𝗜𝗡𝗢𝗣 𝗦𝗬𝗦 entry and a landing performance penalty applies per the QRH. For 𝗦𝗘𝗖 𝟭 or 𝗦𝗘𝗖 𝟮 failure specifically, the elevator backup capability is now degraded - one of the two SECs that can provide pitch backup is gone, and only the remaining one is available if both ELACs subsequently fail. The pilot does not feel this in normal operation because the ELACs are still flying the airplane.

Why does SEC 1 failure restrict speedbrake on the A320?

𝗦𝗘𝗖 𝟭 controls the No. 3 and No. 4 spoilers, which are the primary speedbrake surfaces. When SEC 1 fails, the ECAM presents 𝗦𝗣𝗗 𝗕𝗥𝗞 𝗗𝗢 𝗡𝗢𝗧 𝗨𝗦𝗘 as a published operational restriction. This is not a slight reduction in speedbrake authority - it is an explicit prohibition.

The restriction exists because the speedbrake function relies on the symmetric deployment of the No. 3 and No. 4 panels, and the loss of SEC 1 removes that capability. A candidate quoting "reduced speedbrake authority" rather than "SPD BRK DO NOT USE" has the wrong mental model and an examiner will press on it. The landing performance penalty for SEC 1 failure is more substantial than for SEC 2 or SEC 3 failure because the speedbrake restriction affects the available deceleration profile on approach and landing.

What happens if all three SECs fail on the A320?

A triple-SEC failure (𝗙/𝗖𝗧𝗟 𝗦𝗘𝗖 𝟭+𝟮+𝟯 𝗙𝗔𝗨𝗟𝗧) reverts the airplane to 𝗔𝗟𝗧𝗡 𝗟𝗔𝗪 with 𝗣𝗥𝗢𝗧 𝗟𝗢𝗦𝗧. All SEC-controlled roll spoilers are lost. The direct-law reversion that follows is 𝗰𝗼𝗻𝗳𝗶𝗴𝘂𝗿𝗮𝘁𝗶𝗼𝗻-𝗱𝗿𝗶𝘃𝗲𝗻, not autopilot-state-driven.

Direct Law Trigger - Configuration-Gated, Not AP-Disconnect:

• AP engaged at failure → WHEN L/G DN AND AP OFF: DIRECT LAW • No AP engaged → WHEN L/G DN: DIRECT LAW • ELAC substitution: CONF 2 instead of L/G DN when active

The common wrong answer in oral exams is "direct law on AP disconnect." That is incorrect. The trigger is tied to landing configuration, not autopilot state alone. The right answer quotes the FCOM conditions exactly and treats them as configuration-gated rather than improvising about AP timing.

What happens if one FAC fails on the A320?

A single FAC failure (𝗔𝗨𝗧𝗢 𝗙𝗟𝗧 𝗙𝗔𝗖 𝟭(𝟮) 𝗙𝗔𝗨𝗟𝗧) transfers all FAC functions to the surviving FAC. The pilot does not feel a handling change. The PFD speed scale still shows characteristic speed markers and the rudder still has its variable travel limiter.

Single FAC Failure - What Continues, What Degrades:

• All FAC functions → surviving FAC • Yaw damping, turn coordination, rudder trim, travel limit preserved • Characteristic speeds, alpha-floor, windshear, low-energy preserved • Status: BOTH PFD ON SAME FAC • Autoland: CAT 3 SINGLE ONLY (CAT 3 DUAL lost)

Any approach to minima below CAT 3 SINGLE requires the redundancy that no longer exists, and the candidate who shrugs and continues without noticing the operational change discovers it at the worst possible moment.

What happens if both FACs fail on the A320?

A dual FAC failure (𝗔𝗨𝗧𝗢 𝗙𝗟𝗧 𝗙𝗔𝗖 𝟭+𝟮 𝗙𝗔𝗨𝗟𝗧) produces a law outcome that is 𝗲𝗳𝗳𝗲𝗰𝘁𝗶𝘃𝗶𝘁𝘆-𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁. The FCOM specifies different consequences for different MSN groups, and the article-level rule is that there is no single universal answer.

Law Outcome - Varies by MSN Group:

• Some MSN groups → F/CTL ALTN LAW (PROT LOST), WHEN L/G DN: DIRECT LAW • Other MSN groups → ALTN LAW, no DIRECT LAW reversion at gear down • Correct answer: quote the law table for the operator's effectivity

The candidate-intuitive answer that "dual FAC failure leaves us in normal law as long as the ELACs are healthy" is wrong for every MSN group. The FCOM specifies a law reversion in all cases.

Functions Lost (Common Across Effectivity Groups):

• Yaw damping • Turn coordination • Rudder trim • Characteristic speeds on PFD • Alpha-floor (inhibited - ALTN law) • Windshear detection • Low-energy warning

Operational Status / Limits:

• Rudder travel limiter LOCKED at second-failure value • ECAM: RUD WITH CARE ABV 160 KT • Full rudder travel recovered at slats extension • Approach: APPR SPD VREF + 10 KT • OPERATING SPD COMPUTE where applicable • NO DISPATCH - MEL

Where do A320 characteristic speeds come from?

The dynamic characteristic speeds on the PFD speed scale (𝗩𝗟𝗦, 𝗩𝗙𝗘, 𝗩𝗠𝗢, 𝗩𝗠𝗔𝗫, 𝗙-𝘀𝗽𝗲𝗲𝗱, 𝗦-𝘀𝗽𝗲𝗲𝗱, 𝗴𝗿𝗲𝗲𝗻 𝗱𝗼𝘁) are computed and displayed by the FACs. The FAC controls the PFD speed scale.

Characteristic Speed Source Chain:

• ADIRUs → raw air data (airspeed, altitude, AoA, temperature) • FAC → computation and display layer • MSN 06003-07077: FAC uses FMS gross weight • FAC GW/CG computation available as backup

A total FAC failure removes the characteristic speed overlays without affecting the underlying air data. If both FACs fail, raw airspeed remains on the PFD - the characteristic speed markers disappear, but the airspeed itself does not. The examiner trap is the candidate who answers "the ADIRUs" alone when asked where the characteristic speeds come from. The right answer names the 𝗙𝗔𝗖 as the computation and display layer and acknowledges the FMS gross weight relationship on newer effectivity.

Is the A320 rudder mechanical or electronic?

The A320 rudder has two control paths.

The Two-Path Rudder Design:

• Pedal path → MECHANICAL (no computer in the linkage) • Rudder surface → hydraulically actuated by three servojacks • FAC electrical functions → yaw damp, turn coord, trim, travel limit • Dual FAC failure → loses electrical, KEEPS mechanical pedal authority

The two-path design matters operationally because dual FAC failure removes the electrical rudder control functions but does not remove the mechanical pedal authority. The pilot retains direct mechanical rudder authority with no augmentation, which is a fundamentally different situation than "no rudder at all." The mechanical pedal-to-rudder linkage is a deliberate design feature that preserves yaw control through certain failure scenarios that would otherwise eliminate it.

Why is alpha-floor inhibited after dual FAC failure on the A320?

Alpha-floor is inhibited because the airplane is in 𝗮𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗹𝗮𝘄. The FCOM wording is simply that alpha-floor protection is inhibited when alternate or direct law is active. The mechanism is not a multi-step causal chain involving autothrust degradation or FAC dependency on the autothrust system. It is a published rule about which law states permit alpha-floor and which do not.

Candidates who try to construct a causal explanation in an oral exam invite follow-up questions they cannot defend. The clean answer quotes the FCOM rule: 𝗮𝗹𝗽𝗵𝗮-𝗳𝗹𝗼𝗼𝗿 𝗶𝘀 𝗶𝗻𝗵𝗶𝗯𝗶𝘁𝗲𝗱 𝗶𝗻 𝗮𝗹𝘁𝗲𝗿𝗻𝗮𝘁𝗲 𝗼𝗿 𝗱𝗶𝗿𝗲𝗰𝘁 𝗹𝗮𝘄, and the dual FAC failure puts the airplane in alternate law, which is why alpha-floor is inhibited. The reasoning ends there. Inventing a homemade causal chain is a quick way to give an examiner somewhere to drill.

Foundation Series

This Page Completes the Foundation Series

These answers cover the SEC and FAC architecture at a search-intent level. The A320 Oral Exam Prepper covers it at the examiner-grade depth that an oral exam actually demands: every trap, every citation, every consequence, with the conversational format that lets you practice thinking out loud before the real oral. The airline-specific variants are anchored to the operator's exact FCOM effectivity, which matters specifically for cases like the dual-FAC law table that varies across MSN groups.

Read the full Week 3 article on LinkedIn: "The Quiet Ones in the Corner: The Five Computers That Do the Unglamorous Work."

Foundation Series Navigation

Spoke 1 - ELAC, SEC, FAC Foundation
Live June 4 · /a320-flight-control-computers-the-foundation-guide/

Spoke 2 - ELACs Deep Dive
Live June 11 · /a320-elacs-deep-dive/

↳ You are here: Spoke 3 - SECs & FACs Deep Dive
/a320-secs-facs-deep-dive/

Hub - Full Architecture Guide
/a320-elac-sec-fac/

FCOM Documentation

Manual References

[FCOM] §DSC-27-10-10, Flight Control Computers - General Description (p. 2-4/6)
[FCOM] §DSC-27-10-30, SEC Architecture and Functions
[FCOM] §DSC-27-10-40, FAC Architecture and Functions
[FCOM] §DSC-22_40-10, Rudder Control Architecture (p. 1/2)
[FCOM] §DSC-22_40-30, Characteristic Speed Computation and FMS GW (p. 1-3/6)
[FCOM] §DSC-27-20-20, Law Reconfiguration and ALTN Protections (p. 4-7/24)
[FCOM] §PRO-ABN-F_CTL, F/CTL SEC 1(2)(3) FAULT Procedure
[FCOM] §PRO-ABN-F_CTL, F/CTL SEC 1+2+3 FAULT (triple-SEC cascade)
[FCOM] §PRO-ABN-AUTO_FLT, AUTO FLT FAC 1(2) FAULT (p. 5/36)
[FCOM] §PRO-ABN-AUTO_FLT, AUTO FLT FAC 1+2 FAULT (p. 7-17/36)
[FCOM] §PRO-ABN-AUTO_FLT, APPR SPD and OPERATING SPD COMPUTE (p. 8, 11, 14, 17/36)
[FCOM] §PRO-ABN-F_CTL, Status Notes (WHEN L/G DN: DIRECT LAW, AP-state conditions)
[MEL] 27-95-01, SEC dispatch requirements
[MEL] 27-97-01, FAC NO DISPATCH classification
[QRH] F/CTL Summary pages, SEC and FAC failure consequences