Law Reconfiguration — the Degradation Map from Normal to Mechanical

This article ties the whole law chain together: how the EFCS degrades gracefully from Normal law down through Alternate, Direct and Mechanical as failures accumulate, what triggers each step, how the handling technique changes at each level, and how the PFD and ECAM always tell the crew which law they are in. It is the map that the protection and law articles (05–16) hang on.

Depending on the type of failures affecting the flight control system, or its peripherals, there are 3 possible reconfiguration levels: Alternate law (ALT 1 or ALT 2), Direct law, or Mechanical. — FCOM DSC-27-20-20-10

1. The degradation ladder — and the handling at each level

Per FCOM DSC-27-20-20-10, below Normal law there are three reconfiguration levels (Alternate, Direct, Mechanical), plus the separate Abnormal-Attitude branch:

[!note]- The spine is "protections → stabilities → nothing", and the technique shifts with it (integrative synthesis) Read the table top-to-bottom: Normal law has full protections (fly hands-light); Alternate keeps only maneuver protection and turns the rest into over-ridable stabilities (you can now stall/overspeed, roll is direct); Direct has no protections, only warnings, loses auto-trim (conventional manual trimming returns, recovery is manual); Mechanical is THS wheel (pitch) + BCM (yaw) (coarse survival flying). Roll degrades to direct already at Alternate and gets faster (15 → 20–25°/s) — so small lateral inputs matter from Alternate down. This single progression is the thread through articles 05–15.

2. What triggers each step

Per FCOM DSC-27-20-20-10 and the architecture (01):

• Normal → Alternate: failures of computers, hydraulics or sensors that prevent the full protections (protection is totally lost on a VS1g computation failure — loss of weight or slat/flap position; lost on a dual/triple ADR failure or ADR DISAGREE);
• ALT 1 vs ALT 2: ALT 2 has no bank-angle protection; a dual ADR failure removes low-speed stability, a triple ADR failure removes high-speed stability;
• Alternate → Direct: further failures (and the low-speed-stability boundary reverts to direct);
• Direct → Mechanical: both elevators failed → pitch on THS wheel only (MAN PITCH TRIM ONLY red); total electrical or PRIM+SEC loss → rudder on the BCM;
• Abnormal attitude: an extreme attitude (14) — a separate branch that settles into Alternate/Direct afterwards.

[!warning]- Air data drives much of the degradation — and a jerk may be felt A large share of the Normal→Alternate→ALT 2 path is air-data (ADR/AOA) dependent (FCOM DSC-27-20-20-10) — lose trustworthy speed/AOA and the protections cannot be computed (the unreliable-airspeed case). A jerk may be felt at reconfiguration (hydraulic failure, computer failure, electrical transient) — a normal symptom of the handover. And losing green hydraulics changes the master computer to P2 (01).

3. The electrical path into the ladder

A non-flight-control failure can also walk you down the ladder. Per FCTM PR-AEP-ELEC, the electrical emergency configuration flies in alternate law, reverting to direct law when the landing gear is extended (LAND RECOVERY ON); on RAT-only power, AP, pitch trim and rudder trim are not available and the aircraft is out of trim in roll.

[!note]- "ALTN LAW" on the ECAM may be a power problem, not a flight-control one (integrative synthesis) The same degraded-law annunciation can come from the flight-control system itself or from the electrics feeding it (02 PSDU, 24 BCM/BPS). A deep electrical loss puts you in alternate, then direct on gear extension for landing (FCTM PR-AEP-ELEC) — so reading the ECAM electrical status alongside the F/CTL law tells you why you are degraded and what else (AP, trims) you have lost.

4. The cockpit cues — always know your law

Per FCOM DSC-27-20-20-10, the law status is always annunciated:

[!warning]- The PFD speed scale and the trim message tell you the law — and the technique — at a glance Airbus deliberately puts the law on the PFD: green = = protected (hands-light); amber X = a protection lost; VSW barber pole = no alpha protection (you can stall → reduce-AOA recovery); amber USE MAN PITCH TRIM = trim manually; red MAN PITCH TRIM ONLY = elevators gone (FCOM DSC-27-20-20-10). One scan tells the crew what is protected and which technique applies — pull-protected vs reduce-AOA, auto-trim vs manual.

Special cases: dual RA failure introduces flare law when gear is down and both APs are off (the 50 ft pitch-down no longer applies); a single SEC can fly the aircraft in direct law, and one computer of any type suffices (01).

5. Counterintuitive points

[!warning]- Roll goes direct early; pitch degrades later Roll is already direct in Alternate law, while pitch keeps its load-factor demand until Direct law (FCOM DSC-27-20-20-10/-20) — the axes do not degrade together, and small roll inputs matter from Alternate down.

[!warning]- Recovery from an upset doesn't restore Normal law The abnormal-attitude branch settles into Alternate/Direct for the rest of the flight (14).

[!warning]- A non-flight-control failure can put you in alternate/direct The electrical emergency configuration flies alternate/direct (FCTM PR-AEP-ELEC).

6. Self-test

[!note]- Q1. The reconfiguration levels in order, and how does technique change down them? Normal → Alternate (ALT 1 / ALT 2) → Direct → Mechanical (+ Abnormal-Attitude); technique goes hands-light → small roll inputs (can stall) → manual trimming/recovery → coarse survival flying.

[!note]- Q2. What largely drives Normal → Alternate → ALT 2 degradation? Air data — VS1g computation failure, dual/triple ADR failure or ADR DISAGREE; ALT 2 also drops bank protection.

[!note]- Q3. What two failures define the Mechanical level? Both elevators failed → pitch on THS trim wheel (MAN PITCH TRIM ONLY); total electrical / PRIM+SEC loss → rudder on the BCM.

[!note]- Q4. How does the PFD show "you can stall now", and which non-flight-control failure degrades the law? VαPROT/VαMAX → VSW barber pole (green = → amber X); the electrical emergency configuration flies alternate/direct.

7. Key takeaways

References

• FCOM DSC-27-20-20-10 (Reconfiguration Control Laws — General) — three levels (alternate ALT 1/ALT 2, direct, mechanical); protection totally lost on VS1g computation failure (weight or slat/flap position loss), lost on dual/triple ADR failure or ADR DISAGREE; ALT 1 keeps bank-angle limitation (roll normal) with PFD marks amber; both elevators failed → pitch mechanical backup via manual pitch trim (MAN PITCH TRIM ONLY red); dual RA failure → flare law when gear down + both AP off (no 50 ft pitch-down); reconfiguration jerk; ECAM FLT CTL ALTN LAW (PROT LOST) 330 kt/M 0.82, DIRECT LAW 330 kt/M 0.80 MAN PITCH TRIM USE; PFD amber X for lost protection, VαPROT/VαMAX → VSW, USE MAN PITCH TRIM.
• FCOM DSC-27-20-20-20 / -30 / -40 / -50 — Alternate, Direct, Abnormal-Attitude and Mechanical-Backup details (articles 12–15).
• FCTM PR-AEP-ELEC — electrical emergency configuration flies alternate law, direct law on landing-gear extension (LAND RECOVERY ON); RAT-only EMER GEN: no AP/pitch trim/rudder trim, out of trim in roll.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.