Lateral Normal Law and Bank Angle Protection

Five earlier articles in this chapter all live on the pitch axis — the C* load-factor law, angle-of-attack, high-speed, pitch-attitude and load-factor protections. This one turns the camera to roll. In pitch, the A330 gives you a load-factor demand: pull and you ask for g, release and you ask for 1 g along the present path, so you are feeding the stick almost continuously. In roll the philosophy is different and, for the pilot, far more hands-off: the sidestick is a roll-rate demand, and once a bank is set the computers hold it for you, trim roll automatically, coordinate the rudder, and damp the dutch roll — so you let go between "rolling in" and "rolling out". This article covers that lateral Normal Law, the bank-angle protection that wraps a soft wall around it, and the sideslip target the system paints blue after an engine failure.

One boundary first, because it re-frames everything below:

[!warning]- Everything here is Normal Law only. Do not carry "roll is direct" up from the degraded-law articles.

In Normal Law the roll axis is a protected, rate-demand law with a bank-angle soft wall. That is not how it behaves once the law degrades — in the lower reconfiguration laws the roll axis can revert to a direct stick-to-surface relationship with no bank protection. The split (which degraded law keeps near-normal roll and which goes direct) belongs to Alternate Law and Direct Law. Read this article as "what a healthy aircraft does", and treat the green protection symbol on the PFD (§5) as your live confirmation that all of it still applies.

1. Roll-rate demand — and the three flight modes

Like the pitch law, the lateral law runs through ground / flight / flare modes, and the transitions are automatic and smooth. The whole behaviour is set out in one FCOM subsection; this article works through it block by block.

1.1 Ground mode — direct, scaled by speed

On the ground the lateral law is a direct relationship: stick deflection produces surface deflection, but the gain is scaled by airspeed so the same stick gives less surface as the aircraft accelerates. Per FCOM DSC-27-20-10-30:

When the aircraft is on ground, the sidestick commands the aileron and the deflection of the roll spoiler surfaces deflection. The amount of control surface deflection that results from a given amount of sidestick deflection depends on the aircraft speed. The pedals control rudder deflection. The aircraft smoothly transitions to flight mode shortly after liftoff.

For the pilot this means the roll-axis feel during the take-off and landing roll is direct and predictable — you lay on aileron for a crosswind correction and the wing responds immediately, with no "roll-rate" abstraction layered on top. The speed-scaling keeps the surfaces effective at low taxi speeds without over-controlling as speed builds.

1.2 Flight mode — one sidestick, three surfaces, automatic everything

Shortly after lift-off the law becomes a roll-rate demand and folds three surfaces into a single stick. This is the core paragraph of the article. Per FCOM DSC-27-20-10-30:

When the aircraft is in the flight mode, normal law combines the controls of the ailerons, spoilers (except spoilers 1), and rudder (for turn coordination) in the sidestick. The flight crew does not need to use rudder for turn coordination purpose. While in manual flight the flight crew controls the roll and heading, the flight control system automatically limits the roll rate and the bank angle, ensures turn coordination and damps the dutch roll.

and the demand law itself:

The roll rate requested by the flight crew during flight is proportional to the sidestick deflection, with a maximum rate of 15 °/s when the sidestick is in full deflection. When the aircraft is in flare mode, the lateral control is the same as in flight mode.

Three things to pull out:

• "combines … in the sidestick" — one stick simultaneously drives the ailerons, the roll spoilers, and the rudder. You express only how fast you want to roll; how the three surface groups cooperate is the computers' problem. This is precisely why an A330 turn needs no pedal — the rudder's turn-coordination command is computed by the PRIM and blended in for you.
• "proportional … 15 °/s" — the defining number of lateral Normal Law, and the mirror image of the pitch law: full aft stick asks for g, full lateral stick asks for 15 °/s of roll rate.
• automatic roll-rate limit, bank limit, turn coordination, dutch-roll damping — four jobs the system does without you. The bank limit is the bank-angle protection of §3; the dutch-roll damping is why you must keep your feet off the pedals (§7).

1.3 Flare — roll is unchanged

Note the deliberate contrast with pitch. At about 100 ft the pitch law enters flare mode and changes character (auto-trim freezes, the law becomes a flare law — see Normal Law (pitch)). The lateral law does not: "When the aircraft is in flare mode, the lateral control is the same as in flight mode." Your roll feel in the flare — laying on a few degrees of bank to track the centreline, taking it off again — is the same rate-demand law you had in the cruise.

        on ground
   ┌──────────────────────────────┐
   │ GROUND MODE                  │
   │ sidestick → aileron + roll   │
   │   spoilers, deflection ∝     │
   │   stick, scaled by speed     │
   │ pedals → rudder (direct)     │
   └───────────────┬──────────────┘
                   │  smoothly, shortly after liftoff
                   ▼
   ┌──────────────────────────────┐
   │ FLIGHT MODE                  │
   │ sidestick = roll-rate demand │
   │   (∝ stick, max 15 °/s)      │
   │ blends aileron + spoilers    │
   │   (except 1) + rudder        │
   │   (turn coordination)        │
   │ auto: limit roll rate & bank │
   │   · coordinate · damp        │
   │   dutch roll                 │
   └───────────────┬──────────────┘
                   │  flare: lateral law UNCHANGED
                   ▼  touchdown (smooth)
   ┌──────────────────────────────┐
   │ GROUND MODE                  │
   │ back to direct relationship; │
   │ decrab: induced roll limited │
   └──────────────────────────────┘

2. The surfaces blended into one sidestick

The roll axis is built from two ailerons and a set of spoilers per wing, plus the rudder for coordination. Per FCOM DSC-27-10-20:

Two ailerons and five spoilers on each wing control the aircraft about the roll axis. The maximum deflection of the ailerons is 25 °. Ailerons extend when the flaps are extended (aileron droop). The maximum spoiler deflection is 35 °.

That "five spoilers" is exactly the "spoilers (except spoilers 1)" of the lateral-law text: of the six spoiler panels per wing, panel 1 takes no part in roll, leaving panels 2–6 as the five roll spoilers.

The point of the table is that a single roll-rate demand on the stick is resolved by the PRIM into a coordinated package — ailerons and roll spoilers for the roll, rudder for the coordination — which is why the pilot's hands and feet do so little in a routine turn.

3. Bank angle protection — release to level, full stick to a soft wall

This is the signature behaviour of the lateral law. Three sentences fix the whole "33° / 67°" character of the aircraft. Per FCOM DSC-27-20-10-30:

Inside the normal flight envelope, the system maintains positive spiral static stability for bank angles above 33 °. If the pilot releases the sidestick at a bank angle greater than 33 °, the bank angle automatically reduces to 33 °. Up to 33 °, the system holds the roll attitude constant when the sidestick is at neutral. If the pilot holds full lateral sidestick deflection, the bank angle goes to 67 ° and no further.

Read sentence by sentence:

• "holds the roll attitude constant" (≤ 33°) — roll hold. Roll into a 30° turn, release the stick, and the aircraft stays at 30°. This is the physical basis for "set the bank, then let go". A conventional aircraft, being spirally unstable, would slowly overbank if you released; inside 33° the A330 is made neutrally stable — neutral stick freezes the bank.
• "positive spiral static stability" (> 33°) — above 33° the aircraft is given positive spiral stability, so releasing the stick lets it roll back to 33° on its own. There is an invisible "spring home": roll to 50° and release, and it returns to 33°. To hold 50° you must keep a steady lateral pressure on the stick.
• "67 ° and no further" — the full-stick hard cap. Hold the stick fully over and the bank tops out at 67°. This is the roll-axis soft wall, the lateral counterpart to α-max in pitch.

FCOM then describes the two handling regimes directly to the pilot. Per FCOM DSC-27-20-10-30:

During a normal turn (bank angle less than 33 °), in level flight: • The PF moves the sidestick laterally (the more the sidestick is moved laterally, the greater the resulting roll rate - e.g. 15 °/s at max deflection) • It is not necessary to make a pitch correction • It is not necessary to use the rudder. In the case of steep turns (bank angle greater than 33 °), the PF must apply: • Lateral pressure on the sidestick to maintain bank • Aft pressure on the sidestick to maintain level flight.

So 33° is a watershed, and the two sides feel completely different:

[!warning]- 33° is the line between "hands off" and "hands on" — and standard turns sit deliberately on the easy side.

Up to 33° the aircraft is a hands-off machine: the bank holds itself and pitch trims itself, so a 25–30° turn is flown by setting the bank and then largely letting go. Above 33° it becomes a two-handed machine — you hold the bank in laterally and hold the nose up in pitch, because that "spring home" is now pulling you back to 33° the whole time. This is exactly why standard rate / standard bank turns are flown at 25–30°: they sit in the low-workload band, just inside the watershed.

 bank
 angle
  67° ┤═══ full-stick cap, no pitch/speed protection active ═══════
      │
  45° ┤··· full-stick cap when α / high-speed / neg-pitch prot active
      │··· above here: AP drops, FD bars vanish ·······························
  40° ┤··· FD bars return below here  (45° / 40° hysteresis) ··············
      │
  33° ┤─── release stick ABOVE 33° → rolls back to 33° (spiral stable) ──
      │    auto-trim INOP in the > 33° band (bank protection active)
   0° ┤─── release stick AT/BELOW 33° → bank held (roll hold) ──────────
      └──────────────────────────────────────────────────────────────────

4. When the soft wall shrinks — 67° to 45°, and auto-trim stops

The roll soft wall is not a fixed 67°. If a pitch- or speed-axis protection is active, the system judges you to be in a more exposed state and refuses to let you stack bank on top of it. Per FCOM DSC-27-20-10-30:

If angle-of-attack protection, or high speed protection, or negative pitch attitude protection is operative, the bank angle will not go beyond 45 °, when the pilot maintains full lateral deflection on the sidestick. If high speed protection is operative, the system maintains positive spiral static stability from a bank angle of 0 °, so that with the sidestick released, the aircraft always returns to a bank angle of 0 °.

and, separately:

When bank angle protection is active, auto trim is inoperative.

Three things follow:

• The 67° → 45° tightening. If angle-of-attack protection, high-speed protection, or negative pitch-attitude protection is operative, the full-stick cap drops from 67° to 45°. The design intent: you are already against one wall of the envelope, so the system will not let you add a hard manoeuvre on the other axis. This is why this article cannot stand alone from articles 06 / 08 / 09 — the height of the roll wall is set by the state of those three protections.
• High-speed protection even moves the "home" target. Normally the spring home is to 33°; with high-speed protection active the positive spiral stability acts from 0°, so releasing the stick rolls the wings fully level. The logic is that at over-speed any bank adds manoeuvre load and loss-of-control risk, so the system biases you back to the steadiest state.
• Auto-trim stops once bank protection is active, i.e. in the > 33° band — long before the 45° autopilot threshold of §5.

[!warning]- Auto-trim stops at 33° (protection active), not at 45°. These are two different thresholds doing two different jobs.

A common error is "auto-trim stops once you pass 45°". It does not. FCOM gives two separate rules: "when bank angle protection is active, auto trim is inoperative" (that protection is active in the > 33° spiral-stability band), and "if the bank angle exceeds 45 °, the autopilot disconnects". So 33° is the auto-trim threshold and 45° is the autopilot / flight-director threshold — two numbers governing two systems. Mixing them up is a classic exam trap.

5. The 45° line — autopilot drop and PFD declutter

Past 45° of bank the aircraft trips the automatic-flight "let-go" threshold, and the PFD declutters in lock-step. Per FCOM DSC-27-20-10-30:

If the bank angle exceeds 45 °, the autopilot disconnects and the FD bars disappear. The FD bars return when the bank angle decreases to less than 40 °.

The PFD description gives the same 45° / 40° pair for the roll scale. Per FCOM DSC-31-40:

(3) Roll Index (yellow) — This pointer indicates the bank angle. When the bank angle exceeds 45 °, all the PFD symbols except those for attitude, speed, heading, altitude, and vertical speed disappear. The display returns to normal when the bank angle decreases below 40 °.

So the 45° / 40° hysteresis (enter at 45°, restore at 40°, with a 5° gap) prevents the autopilot, flight director, and display from flickering in and out around the threshold. Above 45° the PFD strips back to five core items — attitude, speed, heading, altitude, vertical speed — to help you focus in an abnormal, high-bank state. The roll scale itself is only marked to 45°: per FCOM DSC-31-40, "This scale is white, and has markers at 0, 10, 20, 30, and 45 ° of bank" — running off the end of the scale is itself the visual cue that you are now outside the routine envelope.

There is also a small green "health lamp" on the roll scale telling you whether the whole bank-protection mechanism is even live. Per FCOM DSC-31-40:

(5) Flight Control Protection Symbols — The display shows these symbols (=) in green: ‐ On the roll scale to mark the bank angle protection availability ‐ On the pitch scale at 15 ° nose down or 30 ° nose up to mark the pitch limits. An amber × replaces these symbols, if the corresponding protection is lost.

[!warning]- The green "=" at the ends of the roll scale is your live confirmation that this entire article still applies.

Everything above — the 67°/45° caps, release-to-33°, auto-coordination — only holds in Normal Law. The green "=" on the roll scale is the bank-angle-protection-available lamp. If the law degrades and bank protection is lost, that green "=" is replaced by an amber ×, which is the screen telling you directly: the soft wall is gone, full stick can now roll you past the limit and releasing will no longer level you. A glance at the colour of that symbol is the fastest check of whether this article's conclusions are currently true. (It is the same symbol family as the green "=" at 15° nose-down / 30° nose-up that marks the pitch limits — do not watch only the roll one.) The loss cases sit in Alternate Law and Controls and Indications.

6. Sideslip target (β target) — the blue index after an engine failure

The last product of the lateral law is its yaw-side cooperation. After an engine failure the PFD's sideslip index turns blue, and its meaning changes from "zero sideslip" to "the sideslip that gives best climb performance". Per FCOM DSC-27-20-10-30:

Should an engine failure occur, the sideslip indication is slightly modified to ensure that optimum pilot rudder application is made to achieve optimum climb performance (ailerons to neutral and spoilers retracted). In the case of an engine failure at takeoff, or at go-around, the sideslip index on the PFD changes from yellow to blue (Refer to DSC-31-40 Attitude Data that provides the conditions for the blue display of the sideslip target). In flight, the lateral normal law commands some rudder surface deflection to minimize the sideslip.

and the crew action it implies:

Crew response is normal and instinctive: ‐ Zero, the beta target value for optimum performance with appropriate rudder application ‐ Accelerate if beta target cannot be zeroed with full rudder. The computation is made by the PRIM.

Why change the index from yellow to blue and the target from "zero sideslip" to a "β target"? Because with one engine out, symmetric (zero) sideslip is not the performance optimum. A small amount of sideslip toward the live engine — combined with ailerons neutral and spoilers retracted — minimises drag and maximises climb gradient (it avoids the roll spoilers standing up and eating lift when you hold bank against the asymmetry). The system computes that performance-optimal sideslip for you and paints it as the blue β target; you simply fly it to centre. The pilot action is the simplest possible: zero it with rudder, and if full rudder cannot zero it, accelerate.

The precise conditions for the blue target come from the PFD description. Per FCOM DSC-31-40:

Note: The sideslip target is blue if: ‐ Slats/Flaps are in CONF 1, 1+F, 2, 3 or FULL, and ‐ One thrust lever > MCT (≥ FLX if FLX or DERATED TO), and ‐ At least one engine > 1.3 EPR, and ‐ Engine thrust asymmetry > 0.25 EPR. In this case the sideslip index is called β target. When this index is centered with the roll index, the sideslip equals the sideslip target for optimum aircraft performance.

The index is a lateral-g indication, not a heading angle. Per FCOM DSC-31-40, the trapezoidal index "moves beneath the roll index. On ground, it represents the lateral acceleration of the aircraft. In flight, it shows sideslip (as computed by the PRIM computers). One centimeter of displacement indicates 0.2 g. The sideslip index is against its stop at 0.3 g." So "centring" the β target means trimming out lateral acceleration to the optimum point, and the four conditions exist to confirm a genuine, large take-off/go-around asymmetry before the display switches — preventing a spurious blue index on the ground or in symmetric cruise.

[!warning]- "Zero the sideslip" after engine failure does not mean fly geometric zero sideslip.

The instinct is "an engine failed, so make it symmetric — zero sideslip is least effort." The blue β target says otherwise: the optimum is a slight sideslip toward the live engine (ailerons neutral, spoilers in), which gives the smallest drag and the best climb gradient. "Zero the index" means drive the blue β target to centre — that is the performance point — not drive the aircraft to geometric zero yaw. At take-off / go-around you fly the blue β target; in the cruise / approach you fly the yellow slip index; the physical action is identical: put the small trapezoid directly under the roll index.

7. The rudder red line — pedal discipline

Normal Law protects pitch and roll, but — "as on conventional aircraft" — it does not protect yaw (the stake driven in Flight Control Fundamentals). Since the pedals are the one place a pilot can drive the rudder directly, a roll article has to close the loop on how they may and may not be used. FCTM AS-RUD splits rudder use into a "do" column and a "don't" column — and the "do" column explicitly authorises full rudder against thrust asymmetry. Per FCTM AS-RUD:

B. TO COUNTERACT THRUST ASYMMETRY — Up to full rudder deflection can be used to compensate for the yawing moments that are due to asymmetric thrust.

with the speed caveat:

Note: At high speed (i.e. slats retracted), thrust asymmetry (eg. due to an engine failure) does not have a significant effect on the yaw control of the aircraft. The rudder deflection required to counter an engine failure and center the sideslip is small.

This completes §6 from the "how much pedal" side, and it does not contradict the pedal red line — the prohibition is on using rudder to induce or counter roll and on reversing pedal inputs, not on using rudder against yaw:

• Low-speed single-engine (take-off / go-around, slats out): the yawing moment is large, and full rudder is both legal and harmless to the fin — FCTM lists it under the rudder's designed-for uses. This is the physical backing for §6's "zero it with rudder first, accelerate only if full rudder cannot".
• High-speed single-engine (slats retracted, cruise): the yawing moment is small, so only a little rudder centres the sideslip — do not stamp on it. Same engine-out event, two very different pedal demands.

The authorisation comes immediately before the genuine fin-damaging red line. Per FCTM AS-RUD:

THE RUDDER SHOULD NOT BE USED ‐ To induce roll, or ‐ To counter roll, induced by any type of turbulence. Regardless of the airborne flight condition, aggressive, full or nearly full, opposite rudder pedal inputs must not be applied. Such inputs can lead to loads higher than the limit, and can result in structural damage or failure. The rudder travel limiter function is not designed to prevent structural damage or failure in the event of such rudder system inputs.

The distinction is the whole point: full rudder to counter a steady asymmetric-thrust yaw is authorised; aggressive opposite (reversing) pedal to induce or check roll is prohibited and can exceed the structural limit. "Full rudder" is licensed or not depending on what you are compensating for — a single-direction, steady, real yawing moment versus a back-and-forth, transient load deliberately fed into the airframe. And dutch roll is the law's job, not yours. Per FCTM AS-RUD:

For dutch roll, the flight control laws combined with the natural aircraft damping are sufficient to correctly damp the dutch roll oscillations. Therefore, the flight crew should not use the rudder pedals in order to complement the flight control laws.

This closes the loop on §1.2's "damps the dutch roll": the law already damps it, so adding your own pedal only fights the system and risks stacking structural load. The one landing-phase pedal use the lateral law actively helps with is decrab — and here the roll law limits the roll the pedal would otherwise induce. Per FCOM DSC-27-20-10-30:

During decrab phase, the aircraft limits the induced roll after pedal input, in order to ease flight crew control.

In a crosswind landing you press rudder to decrab and align with the runway; that pedal input would, through roll-yaw coupling, kick off an unwanted roll. The lateral Normal Law suppresses that induced roll so you can concentrate on aligning the nose rather than simultaneously chasing the wings with the stick — a second piece of landing-phase help alongside §1.3's "flare roll = flight roll".

8. Engine failure on the ground — ailerons and spoiler 6 boost yaw

A little-known ground function of the lateral law: during the take-off roll with an engine failed, deflecting the ailerons and spoiler 6 on the opposite wing uses the wing drag difference to add yaw authority and lower VMCG. Per FCOM DSC-27-20-10-30:

In the case of an engine failure during takeoff, the spoiler 6 and ailerons can be deflected on the wing opposite to the failed engine in order to increase yaw efficiency. Note: Increasing yaw efficiency in the case of an engine failure on ground, reduces the VMCG, and therefore increases the takeoff performance.

The trigger requires all five conditions together. Per FCOM DSC-27-20-10-30:

The spoiler 6 and ailerons will be deflected when: ‐ Pedal order is more than 2/3 of full pedal deflection ‐ The aircraft is on ground ‐ The pitch attitude is below 2.5 ° ‐ The speed is above 60 kt ‐ Ground spoilers are not activated.

For the pilot this is fully automatic and transparent — you simply press hard on the rudder (> 2/3 travel) to hold the centreline, and the system raises a little extra drag on the opposite wing to help the rudder, effectively lowering VMCG. It is live only in a narrow window: on the ground, nose still down (< 2.5°), above 60 kt, and with ground spoilers not deployed (i.e. a continued take-off, not a reject or landing roll-out) — a targeted performance assist for the "accelerate and keep it straight" moment of a single-engine take-off.

9. Lateral law across a flight

Stringing §§1–8 into one moving picture:

1. Crosswind take-off roll — you lay on aileron for the crosswind (direct ground law, gain scaled by speed) and hold rudder for the centreline. If an engine fails here with > 2/3 pedal, above 60 kt, nose < 2.5°, the system deflects the opposite ailerons and spoiler 6 to quietly lower VMCG (§8).
2. 25° standard turn after lift-off — roll in with the stick (up to 15 °/s), reach 25° and let go: roll hold freezes the bank, the rudder coordinates automatically (no pedal), auto-trim holds level (no pull). The hands-off band (§3).
3. Rolling out — opposite stick back to wings level, then release again — it stays at 0°. The pedals were never touched.
4. A 50° steep turn (hand-flown) — now you must hold constant lateral pressure (or it spirals back to 33°) and steady aft stick (to hold level). Two-handed band; auto-trim is inoperative (bank protection active).
5. Full-stick avoidance — a hard lateral break tops out at 67°. But if you are also at full aft stick into α-protection, the cap tightens to 45° (§4) — the system will not let you pile bank onto angle of attack.
6. Past 45° — the autopilot drops, the FD bars vanish, the PFD declutters to five core items, flagging the abnormal state; roll back below 40° and the FD bars return (§5).
7. Engine failure after V1 / go-around — TOGA set, the PFD slip index turns blue (CONF ≥ 1, a lever > MCT, > 1.3 EPR, asymmetry > 0.25 EPR). You zero the blue β target with rudder — ailerons neutral, spoilers retracted — for best climb gradient; if full rudder cannot zero it, accelerate (§6). Full rudder here is authorised (§7).
8. Dutch roll / turbulence wing-rock — keep your feet off the pedals: the law plus natural damping already handle it, and pedal "help" only fights the system and risks fin load (§7). Roll with the stick, never induce roll with rudder.

Self-test

[!note]- Q1. Which surfaces does lateral Normal Law combine into the sidestick, and why do you not press the rudder in a turn?

It combines the ailerons (two per wing, 25° max), the roll spoilers 2–6 (five per wing, except spoiler 1, 35° max), and the rudder for turn coordination. You do not press the pedals because the rudder's turn-coordination command is computed by the PRIM and blended into the stick — you express only a roll rate (full stick = 15 °/s) and the computers apportion aileron, spoiler, and rudder. FCOM states the crew "does not need to use rudder for turn coordination purpose". The limit of that, though, is "for turn coordination" only: ground directional control, decrab, and single-engine yaw still need active pedal.

[!note]- Q2. You release the stick at 20°, then at 40°, then at 60°. What does the aircraft do each time, and why is 33° the pivot?

At 20° (≤ 33°): roll hold freezes the bank — it stays at 20°. At 40° and 60° (> 33°): positive spiral static stability rolls it back to 33° on its own. 33° divides the bank-hold region from the auto-return region: inside 33° the aircraft is neutrally stable (neutral stick = stay put); above 33° there is a "spring home" pulling you back to 33°. So holding more than 33° needs constant lateral pressure, while inside 33° you can let go.

[!note]- Q3. What is the full-stick bank cap, and when does it tighten? What else changes at that point?

Full stick normally tops out at 67° and no further. The cap tightens to 45° whenever angle-of-attack protection, high-speed protection, or negative-pitch-attitude protection is operative — the system will not let you stack bank onto an already-exposed pitch/speed state. Additionally, with high-speed protection active the spiral-stability "home" target moves from 33° to 0°, so releasing the stick rolls the wings fully level.

[!note]- Q4. At what bank does auto-trim stop, and at what bank does the autopilot drop? Why is "auto-trim stops above 45°" wrong?

Auto-trim stops once bank-angle protection is active, i.e. as soon as you pass 33° into the spiral-stability band ("when bank angle protection is active, auto trim is inoperative"). The autopilot disconnects and the FD bars disappear above 45° (returning below 40°). "Auto-trim stops above 45°" is wrong: auto-trim has already stopped at 33° — 45° is the AP / FD / PFD-declutter threshold, 33° is the auto-trim threshold. Two numbers, two systems.

[!note]- Q5. After an engine failure the slip index turns blue. What are the four conditions, and do you "zero it" or "accelerate"?

The index turns blue (becomes the β target) when, together: slats/flaps in CONF 1, 1+F, 2, 3 or FULL; one thrust lever > MCT (≥ FLX if FLX/derated); at least one engine > 1.3 EPR; and thrust asymmetry > 0.25 EPR. The action is instinctive: use rudder to zero the β target (ailerons neutral, spoilers retracted, for best climb gradient); if full rudder cannot zero it, accelerate. The β target is the performance-optimal slight sideslip, not geometric zero, and the PRIM computes it.

[!note]- Q6. Full rudder against an engine failure is authorised, yet "full opposite rudder" is forbidden. How do you reconcile that?

They describe different inputs. Up to full rudder against steady asymmetric-thrust yaw is an authorised, designed-for use (large at low speed / slats out; only small at high speed / slats in). What is forbidden is aggressive, full or nearly full, opposite (reversing) pedal used to induce or counter roll — that can exceed the structural limit and damage the fin, and the rudder travel limiter is not designed to prevent it. The licence depends on what you are compensating for: a single-direction, steady, real yawing moment (allowed) versus a back-and-forth transient deliberately loaded onto the airframe (prohibited). Dutch roll, likewise, is left to the law, not the pedals.

Key takeaways

The lateral law is the chapter's clearest example of "the computer does the housekeeping": you ask for a roll rate, and it holds the bank, trims the roll, coordinates the rudder, damps the dutch roll, and — engine out — even paints you the optimum sideslip. Your job narrows to the stick, a disciplined foot on the rudder, and watching the green "=" that says it is all still true.

References

Per FCOM DSC-27-20-10-30 (Lateral Normal Law — ground/flight/flare modes; roll-rate demand 15 °/s; blending of ailerons, spoilers except 1, and rudder for turn coordination; bank-angle protection 33°/67°; normal vs steep turn technique; 67° → 45° tightening under α / high-speed / negative-pitch protection; high-speed protection spiral stability from 0°; auto-trim inoperative when bank protection active; AP disconnect and FD-bar logic at 45°/40°; decrab induced-roll limiting; engine-failure-at-take-off spoiler 6 / aileron yaw boost and its five conditions; sideslip indication after engine failure, β target, zero-or-accelerate crew response, PRIM computation). Per FCOM DSC-27-10-20 (Roll Control — two ailerons + five spoilers per wing, 25° aileron / 35° spoiler, aileron droop). Per FCOM DSC-31-40 (Attitude Data on the PFD — roll scale markers to 45°; Roll Index declutter above 45°, restore below 40°; Flight Control Protection Symbols, green "=" / amber ×; Sideslip Index 0.2 g/cm and 0.3 g stop; β target blue conditions). Per FCTM AS-RUD (rudder operational recommendations — full rudder authorised to counteract thrust asymmetry, small at high speed; rudder not to induce/counter roll, no reversing inputs, structural-load warning, travel limiter not protective; dutch roll damped by the law, not the pedals). The aerodynamic rationale for the β target (a slight sideslip toward the live engine giving least drag / best climb gradient) and the explicit "33° is the auto-trim threshold while 45° is the autopilot threshold" contrast are integrative synthesis drawn from the cited FCOM statements, not single verbatim manual sentences. Degraded-law roll behaviour and the surface-actuation internals are deferred to Alternate Law, Ailerons, Spoilers, and Rudder and Yaw.

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.