Airbus Flight Instructor
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Alternate Law — Protections Become Stabilities, ALT 1 vs ALT 2

Alternate law is the first rung down the degradation ladder. The pitch feel is almost unchanged — it stays a load-factor demand — but the hard protections are gone, replaced by soft, over-ridable stabilities, and roll becomes direct. The headline: in alternate law the aircraft can be stalled or overspeeded, so the crew must fly within the limits themselves. This article covers the law, the ALT 1/ALT 2 split, what an overspeed does without the hard protection, and a common way into alternate law.

Alternate law in pitch is almost the same for the pilot, as normal control law. However, alternate law does not maintain any of the protections, except maneuver protection. — FCOM DSC-27-20-20-20

1. The reconfiguration levels and their cockpit cues

Per FCOM DSC-27-20-20-10, below Normal law there are three reconfiguration levels: Alternate (ALT 1 / ALT 2), Direct, and Mechanical. The cues are consistent:

Indication Meaning
ECAM FLT CTL ALTN LAW (PROT LOST) alternate law; A330 MAX SPEED 330 kt / M 0.82
ECAM FLT CTL DIRECT LAW (PROT LOST) direct law; A330 MAX SPEED 330 kt / M 0.80, MAN PITCH TRIM USE
PFD amber X (instead of green =) a protection is lost
PFD amber USE MAN PITCH TRIM auto pitch trim no longer available

[!note]- The PFD speed scale tells you the law at a glance (integrative synthesis) Airbus puts the law status on the PFD: green = symbols mark available protections in Normal law; when protections are lost they become amber crosses (X), and VαPROT/VαMAX vanish, replaced by a black-and-red barber pole topped by the stall-warning speed (VSW) (FCOM DSC-27-20-20-10/-20). One look at the speed scale tells the crew whether they are protected. A jerk may be felt at the moment of reconfiguration.

2. Alternate pitch — maneuver protection only

Per FCOM DSC-27-20-20-20, in pitch alternate law keeps only the maneuver (load-factor) protection; all others are gone. MMO is reduced (to M 0.82). At low speed the scale changes markedly: VLS remains, but VαPROT and VαMAX disappear, replaced by a single black-and-red strip topped by the stall-warning speed (VSW) — and VSW is g-sensitive (unlike the stable VLS), giving extra margin in turns. Alternate reverts to FLARE law at 100 ft for landing.

[!warning]- The load-factor protection stays, but the stall and overspeed protections do not — you can stall or overspeed The one hard protection retained is load factor (you still cannot overstress) — but high-AOA, alpha-floor, high-speed and pitch-attitude protections are gone (FCOM DSC-27-20-20-20). The αMAX hard stop is replaced by a stall warning you can fly through; near the stall the recovery is the conventional reduce-AOA-first technique (nose-down, level wings, then energy). This is the defining difference from Normal law: the aircraft can be stalled or overspeeded, and the PF must respect the limits manually.

3. Alternate roll — direct

Per FCOM DSC-27-20-20-20, roll control is direct in alternate law: the roll rate is generally higher than normal law and the aircraft at first appears very sensitive; bank stability and limits are no longer active. The crew must take care to remain within normal bank limits.

[!warning]- Roll goes direct and sensitive the moment you enter alternate law Unlike pitch (which still feels like Normal law), roll is immediately direct — stick to surface, higher roll rate, no bank protection or hands-off bank hold (FCOM DSC-27-20-20-20). This is the handling change a crew feels first: smooth pitch, twitchy roll. Make small lateral inputs.

4. ALT 1 — the speed stabilities

Per FCOM DSC-27-20-20-20, ALT 1 provides soft stabilities (not protections — all are over-ridable):

[!warning]- "Stability" means it nudges you and you can override it — and alpha floor is gone The low/high-speed behaviours in alternate are stabilities, not protections: a gentle nose-down near the stall and nose-up past VMO/MMO that the pilot can override (FCOM DSC-27-20-20-20). They encourage the envelope but do not enforce it — and alpha floor is gone, so no automatic TOGA. Recovery is on the crew.

5. What an overspeed does in alternate (and where high-speed protection still acts)

Per FCTM PR-AEP-MISC (Overspeed Recovery): apply the recovery if speed exceeds VMO/MMO — keep the AP engaged, extend speedbrakes to the appropriate position, and if A/THR is ON keep it engaged checking thrust reduces to idle (no operational advantage in manually setting idle — "the engine thrust reduction is the same in both cases"); if A/THR is OFF, set thrust levers to idle. "In the case of severe overspeed, the AP automatically disengages and then the high speed protection activates (except in direct law). As a result, the aircraft encounters an automatic pitch up."

[!warning]- High-speed protection still acts in alternate — but not in direct A key nuance: a severe overspeed disengages the AP and then high-speed protection activates with an automatic pitch-up — "except in direct law" (FCTM PR-AEP-MISC). So in alternate law the high-speed stability (over-ridable nose-up) operates, and a severe overspeed still gets the protective pitch-up; only in direct law is even that gone. The overspeed recovery technique (AP on, speedbrakes, idle thrust) is the same in principle, but the automatic help thins out as you degrade.

6. ALT 2 — even less

Per FCOM DSC-27-20-20-20, ALT 2 protections are identical to ALT 1, except:

  1. no bank-angle protection in ALT 2;
  2. dual ADR failure → no low-speed stability;
  3. triple ADR failure → no high-speed stability.

[!note]- ALT 2 is what an ADR/air-data degradation costs you (integrative synthesis) The difference between ALT 1 and ALT 2 is largely air-data dependent: ALT 2 loses bank-angle protection, and a dual/triple ADR failure further strips low-speed then high-speed stability (FCOM DSC-27-20-20-20). This is why the reconfiguration-general notes tie protection loss to VS1g computation failure and dual/triple ADR DISAGREE — without trustworthy speed/AOA the stabilities cannot be computed. An unreliable-airspeed event is a classic path into ALT 2.

7. A common way in — the electrical emergency configuration

Per FCTM PR-AEP-ELEC, in the ELEC EMER CONFIG the aircraft flies in alternate law (the FLY column lists "PFD 1, … alternate law"); with LAND RECOVERY ON, direct law is selected when the landing gear is extended. With the EMER GEN powered only by the RAT, AP, pitch trim and rudder trim are not available and the aircraft is out of trim in roll (right outboard aileron up).

[!note]- Alternate law is not only a flight-control failure — a deep electrical loss puts you there too (integrative synthesis) The degradation map is reached by many paths. A major electrical failure (ELEC EMER CONFIG) leaves you in alternate law, reverting to direct law on gear extension for landing (FCTM PR-AEP-ELEC) — and on RAT-only power you also lose AP and the trims. So "alternate law" on the ECAM may be the flight-control system itself, or a symptom of a power problem feeding it (electrical backup, 02 PSDU).

8. Counterintuitive points

[!warning]- In alternate law you can stall and overspeed the aircraft Only load-factor protection remains; high-AOA/alpha-floor/high-speed/pitch-attitude are lost (FCOM DSC-27-20-20-20). VSW replaces αMAX as a warning, not a stop.

[!warning]- Pitch feels normal, roll goes direct Pitch stays load-factor demand; roll becomes direct and sensitive immediately (FCOM DSC-27-20-20-20).

[!warning]- High-speed protection still gives a pitch-up in alternate — but not in direct Severe overspeed → AP disengages → automatic pitch-up, except in direct law (FCTM PR-AEP-MISC).

9. Self-test

[!note]- Q1. Which protection does alternate law keep, and which are lost? Keeps maneuver (load-factor) protection; loses high-AOA, alpha-floor, high-speed, pitch-attitude — replaced by over-ridable stabilities and a stall warning.

[!note]- Q2. What happens to roll in alternate law? Direct — higher roll rate, sensitive, no bank stability/limit (ALT 1 keeps bank-angle limitation; ALT 2 does not).

[!note]- Q3. What does a severe overspeed do in alternate vs direct law? In alternate the AP disengages and high-speed protection gives an automatic pitch-up; in direct even that is gone.

[!note]- Q4. The ALT 1 vs ALT 2 difference, and a common way into ALT 2? ALT 2 has no bank-angle protection, and loses low-speed stability (dual ADR) / high-speed stability (triple ADR); unreliable airspeed is a classic path in.

[!note]- Q5. What law does the electrical emergency configuration give? Alternate law (direct law on gear extension with LAND RECOVERY ON); on RAT-only power, no AP/pitch trim/rudder trim, out of trim in roll.

10. Key takeaways

Point Detail
Pitch load-factor demand (feels normal); only maneuver protection kept; MMO → M 0.82; flare law at 100 ft
Roll direct, sensitive, no bank stability (ALT 1 keeps bank limit)
Low speed low-speed stability (IAS nose-down, over-ridable), STALL warning, αfloor inoperative
High speed high-speed stability (over-ridable); OVERSPEED warning remains; severe overspeed → AP off + auto pitch-up (not in direct)
Lost pitch-attitude protection; (ALT 2) bank-angle protection; ADR-dependent stabilities
Way in flight-control failures; ELEC EMER CONFIG (alternate, direct on gear down)
Cues ECAM ALTN LAW (PROT LOST) 330/M0.82; PFD amber X, VSW barber pole, USE MAN PITCH TRIM

References

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.

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