Load Alleviation: MLA, ELAF, and Turbulence Damping

Normal Law makes the aircraft do what you ask: pull the stick, the computers give you a load factor. But Normal Law's job list is much longer than "obey the pilot." While you fly, the Flight Control Primary Computers (PRIM/FCPC) are running a layer of functions you will almost never notice — functions whose only purpose is to protect the two most expensive pieces of structure on the aircraft, the wing and the fin. This article opens that layer up: Manoeuvre Load Alleviation (MLA), Enhanced Load Alleviation (ELAF), turbulence damping, and the aircraft-trimming yardstick that tells you when cruise trim is normal.

What these functions share is the thing that makes them easy to forget: none of them asks you to do anything, and none of them changes the feel of the stick. Pull a hard avoidance manoeuvre and MLA quietly bleeds lift off the outer wing; fly through a patch of turbulence and the damping function micro-flutters the elevator and rudder to kill the structural vibration. All you ever feel is the result — a smoother, lighter-loaded, longer-lived aircraft. There is exactly one switch a pilot can touch in this whole layer: the TURB DAMP pushbutton.

[!warning]- These functions do not limit the g you command, and most of them touch surfaces you would not expect.

Two mental-model corrections up front. First, MLA is not a g-limiter — per FCOM, "the demanded load factor is maintained." It re-shapes the lift distribution inside the g you asked for; it never gives you less g. The g-cap is a separate thing (Load Factor Protection). Second, turbulence damping uses no ailerons at all — it works through the elevator and rudder, because what it is fighting is airframe structural vibration, not the up-and-down bumps you feel. Carry either wrong model into this chapter and the whole layer reads backwards.

1. The silent structural-protection layer

In clean configuration the PRIM run a long list of "laws plus associated functions" simultaneously. Several of them have nothing to do with where you point the nose — they exist purely to keep loads off the structure and to trim the aircraft optimally. Four of them are the subject of this article:

The unifying idea is lift redistribution and active damping in the background. The wing and fin are sized for the worst loads they will ever see; if the system can shave the peak off those loads, the structure can be built lighter, which buys fuel and payload for the life of the airframe. That is what this layer is really doing every time you fly.

By the end you should be able to answer five things:

1. What load is MLA actually relieving, and how does deflecting the outer ailerons + spoilers 4/5/6 upward move the wing's bending moment inboard? What are its two activation thresholds and three availability conditions?
2. Which accelerometers and which surfaces does turbulence damping use? When does it fail permanently for the flight, and when would you deliberately switch it off?
3. MLA and ELAF are both "load alleviation" — what is the difference, and why does ELAF use ailerons only with a completely different trigger?
4. In cruise, what rudder-trim band is normal, and why does the manual quote an asymmetric 1.9° right / 1.6° left range plus a "permanent offset"?
5. Which of these functions survive into Alternate Law and Direct Law? (They do not all drop together.)

2. The map — four functions across one wing

Before the detail, fix where each function acts. The roll surfaces on each wing, running root to tip along the trailing edge, are six spoilers followed by an inboard and an outboard aileron. Per AMM 27-90-00, the manual-law roll/yaw surfaces are the ailerons (inboard and outboard), the spoilers 2 thru 6 and the rudder — note spoiler 1 is not a roll surface; it serves only the speedbrake and ground-spoiler functions.

            RIGHT WING   (root ───────────────────► tip)
 ┌──────────────────────────────────────────────────────────┐
 │  spoilers (ahead of flaps)         ailerons (outer T.E.)  │
 │   ▭    ▭    ▭    ▭    ▭    ▭        ◢────◢   ◢────◢        │
 │   1    2    3    4    5    6        inbd      outbd        │
 └──────────────────────────────────────────────────────────┘
    spoiler 1      = speedbrake / ground spoiler only (no roll)
    spoilers 2..6  = roll  +  speedbrake / ground spoiler
    inbd + outbd   = roll

Now overlay which function borrows which surface:

Four things to read off this:

1. MLA is the wing-wide one. It borrows the outer aileron + inner aileron + spoilers 4/5/6 — all the outboard surfaces — and pushes them up together, dumping outer-wing lift and dragging the lift centre inboard (§3).
2. ELAF is the stripped-down wing function — it borrows the two pairs of ailerons only and never touches a spoiler. That is its sharpest hardware difference from MLA (§5).
3. Turbulence damping is not on this roll-surface picture at all. It works through the elevator (pitch) and rudder (yaw), so its whole row is empty here (§4).
4. MLA and the speedbrake compete for spoilers 4/5/6 — and MLA wins, but only as one link in a longer priority chain (§3.4).

[!warning]- One pair these four functions are easy to blur: same words, different axes and surfaces.

All four are "load relief / trimming," but the axis and the surfaces differ. MLA and ELAF work on the roll surfaces (ailerons / spoilers) to protect the wing; turbulence damping works in pitch and yaw to protect the fuselage and fin. They are not one load-relief function with several names — keep them apart.

3. MLA — pulling wing lift inboard so the wing is bent less

3.1 The idea

Think of the wing as a cantilever beam sticking out of the fuselage. Lift is spread along the span, and the further outboard a slice of lift sits, the longer its moment arm to the wing root — so it does the most to bend the beam upward. Like carrying a bucket of water: the further your hand is from your body, the more your shoulder works. When you haul a high-g manoeuvre (avoidance, a gust), all of that lift scales up together, and the outer-wing lift levers the root hardest, so root bending moment spikes.

MLA's idea is almost embarrassingly simple: you asked for a certain total lift (the load factor), so keep that total — but bleed some lift off the outboard span and let the inboard span carry a little more. Same total lift, but the lift centre moves inboard, and the root bending moment drops. Per FCOM DSC-27-20-10-40:

The purpose of MLA is to redistribute the lift over the wing to relieve structural loads on the outer wing surfaces (bending moment). The demanded load factor is maintained. MLA utilises spoilers 4, 5, and 6 and the ailerons.

That phrase "the demanded load factor is maintained" is the whole division of labour between MLA and the load-factor limitation protection. The limitation protection caps how much g you can command at all (Load Factor Protection); MLA does nothing to that cap — inside the g you asked for, it only re-arranges where the lift sits. One governs the total; the other governs the shape.

3.2 The deflection ledger

How do you "bleed outboard lift"? Deflect the outboard ailerons and spoilers symmetrically upward — an up-deflected surface spoils lift locally, so the outer lift drops and the distribution's centre is forced inboard. FCOM gives the exact accounting. Per FCOM DSC-27-20-10-40:

The MLA becomes active when the sidestick is pulled more than 8°, and the load factor is more than 2 g, in which case: The ailerons are symmetrically-deflected upwards: Maximum of 11° is added to roll demand, if any. Spoilers 4, 5, 6 are symmetrically-deflected: Maximum of 9° is added to roll demand, if any. Deflection is proportional to load factor, in excess of 2 g. An elevator demand is simultaneously applied to compensate for the pitching moment induced by spoilers and ailerons.

Unpack it line by line:

• The two thresholds are AND'd. Stick > 8° and load factor > 2 g — miss either and MLA stays out. This locks MLA to genuine large manoeuvres; everyday 1.x-g corrections never trip it, so cruise efficiency is never disturbed needlessly.
• "Added to roll demand" — it superimposes, it does not override. The up-deflection is added on top of whatever roll you are commanding. If you are already banking, the ailerons are already split one-up-one-down; MLA then adds a symmetric up-bias to both. That is exactly why §2 drew MLA on the roll surfaces — it shares them with roll and the commands sum (Lateral Law).
• "Proportional to load factor, in excess of 2 g" — it eases in. Spoiler deflection grows linearly with how far past 2 g you are: just over 2 g, a trickle; heading toward the cap, more. The relief blends in smoothly rather than snapping on at 2 g.
• Elevator compensation is mandatory, not optional. Up-deflecting the ailerons and spoilers does not only dump lift — it also produces a nose-down pitching moment (lift is spoiled aft, the centre of pressure shifts). Left alone, the aircraft would pitch down and you would lose the g you pulled for. So the PRIM simultaneously feed in an elevator demand to cancel that moment — which is the engineering reason "the demanded load factor is maintained" can be true at all.

The maintenance source confirms the same mechanism from the computer's side and adds the detail FCOM leaves implicit — MLA is tied to the clean configuration. Per AMM 27-90-00:

This FCPC function is activated when the order from a pilot, via the side stick, exceeds a pre-determined load factor in clean configuration. A symmetrical deflection order is sent to the spoilers 4 thru 6 and to the inboard and outboard ailerons. The pitching moments due to MLA deflections are automatically compensated by the pitch control laws. ... This function reduces the design loads during high-g maneuvers demanded by the pilot.

Note the closing words, "reduces the design loads." That is MLA's real engineering payoff: because the worst high-g case is clipped by MLA, the wing box can be designed lighter than it otherwise would be. The saved weight becomes fuel or payload — a structural-mass dividend carried for the life of the aircraft.

3.3 Availability — the three conditions

These three are exam-grade; memorise them. Per FCOM DSC-27-20-10-40:

The load alleviation is only available, when: The aircraft speed is above 250 kt. The FLAPS lever is in the 0 position. In normal or alternate law flight mode. The MLA has priority over the speedbrakes.

Why these three? > 250 kt + clean fences off the high-speed cruise/climb/descent regime — the only place where the dynamic pressure and bending moments are large enough to matter. Slow, with flaps out, on approach, you are neither pulling high g nor anywhere near critical wing bending, so there is nothing to relieve. And "normal or alternate law" is the key survival fact: MLA does not drop when Normal Law is lost — it survives all the way down to Direct Law. Per AMM 27-90-00, listing the functions still available after Normal Law is lost:

The associated functions available are: speedbrake function - ground spoiler function - MLA (except in direct laws) - rudder travel limitation (except for loss of the three ADIRUs) - pedal travel limitation

So MLA is retained in Alternate Law and only lost in Direct Law — it degrades later than turbulence damping and ELAF, which need Normal Law (§4, §5). That is the answer to question 5: these functions do not exit together.

3.4 Priority — where MLA really sits in the chain

The same aileron or spoiler can be wanted by several functions at once — your roll, aileron droop, MLA, the speedbrake. FCOM's headline rule is "the MLA has priority over the speedbrakes," and AMM shows the executable picture. Per AMM 27-90-00:

Taking into account the priority of MLA function over the speedbrake function ... if the MLA is activated when the speedbrakes are extended, spoilers 1 to 3 are retracted to zero and spoilers 4 to 6 are commanded according to MLA orders.

The speedbrake uses the spoiler panels; MLA uses only 4/5/6. When they conflict, the system retracts spoilers 1–3 to zero (surrendering that slice of drag) and hands 4–6 to MLA (keeping the structural relief) — because in a high-g manoeuvre, protecting the wing matters far more than a little extra drag.

But "MLA > speedbrake" is only the adjacent link in a longer chain. AMM pins MLA's true rank among all the functions that can command those surfaces. Per AMM 27-90-00:

As regards the ailerons and spoilers which can receive orders from several laws, the final deflection results from a combination of orders with the priority below: No. 1: roll, No. 2: aileron droop, No. 3: MLA, No. 4: speedbraking. NOTE: On ground, at landing, the ground spoiler function has priority.

  Airborne priority on the ailerons / spoilers:
        No.1  roll              ◄ highest
        No.2  aileron droop
        No.3  MLA
        No.4  speedbraking      ◄ lowest
  On ground, at landing: ground spoiler overrides all of the above

Reading the full chain corrects two common impressions:

• Roll is always No.1. Your bank command outranks droop, MLA and speedbrake at all times — the aircraft guarantees it "obeys your roll" first. This is exactly why the MLA quote said the up-deflection is "added to roll demand": roll is the base, MLA adds on top.
• MLA is not top of the chain — it is No.3. It does beat the speedbrake (No.4), but it yields to roll (No.1) and aileron droop (No.2). So "MLA has priority over the speedbrakes" is a local truth; in the full chain MLA sits in the middle, not at the top.
• On the ground at landing, ground spoiler overrides everything — at touchdown the spoilers must deploy fully to dump lift and plant the weight on the wheels for braking, so the ground-spoiler function trumps every airborne combination. That note is the boundary between the airborne load-relief logic and the on-ground deceleration logic.

What this means for you: you will essentially never be aware of MLA. It works in the one or two seconds of a violent avoidance (TCAS RA, gust, collision avoidance) when you haul the stick back, sparing the wing one over-bending. All you need to carry is: it exists, it guards the wing automatically in a large manoeuvre above 250 kt clean, it is still there in Alternate Law, and it is gone in Direct Law.

4. Turbulence damping — damping structural modes with elevator and rudder

Switch axes. Turbulence hitting the aircraft does more than bounce you up and down: it excites the elastic structural modes of the fuselage and wing — the airframe rings at certain natural frequencies like a tuning fork. Over time that is fatigue; in the moment it is poor ride quality, worst for passengers down the back. Turbulence damping is active vibration cancellation: accelerometers sense the vibration, the computers command surfaces to move in anti-phase, and the vibration energy is cancelled — the same principle as a noise-cancelling headphone emitting an inverted sound wave.

Per FCOM DSC-27-20-10-60:

The purpose of the turbulence damping function is to damp the structural modes induced by atmosphere turbulence. The function uses the Nz accelerometer and two dedicated Ny accelerometers. The PRIMs compute a turbulence damping command, which is added to the normal law command for the elevator and the yaw damper.

Two channels, kept distinct: Nz (vertical acceleration) → elevator damps the longitudinal (pitch/bending) modes; Ny (lateral acceleration) → rudder / yaw damper damps the lateral (yaw/side-bending) modes. AMM details the two "lanes," their redundancy, and where the Ny accelerometer lives. Per AMM 27-90-00:

The Turbulence Damping Function consists of two lanes: 1 Longitudinal lane The longitudinal Turbulence Damping command is computed by the FCPC1 (FCPC2 as a redundancy) as a function of the Nz accelerometer information. It is added to the normal law command and transmitted to the associated elevator servo-controls. 2 Rear lateral lane The rear lateral Turbulence Damping command is computed by the FCPC1 (FCPC2 and FCPC3 as a redundancy) as a function of the information of a specific Ny accelerometer located at the rear bulkhead level. It is added to the normal law command and transmitted to the associated rudder servocontrols.

[!warning]- Turbulence damping touches no ailerons — it works only through the elevator and rudder.

The intuitive guess is that "turbulence damping" fights the bumps with the roll surfaces. It does not touch a single aileron. It targets structural modes — longitudinal bending of the fuselage, lateral swaying of the tail — and the elevator and the aft-fuselage rudder are precisely the surfaces best placed to suppress those modes. The dedicated Ny accelerometer is mounted at the rear bulkhead because the tail is where the lateral structural vibration has its largest amplitude — putting the sensor where the airframe moves most is what lets it measure, and cancel, accurately. (The "largest-amplitude" rationale is engineering reasoning; the rear-bulkhead location is the manual fact.)

4.1 Availability and the two ways it can stop

This is the operationally important part. Per FCOM DSC-27-20-10-60:

This function is automatically monitored and becomes inoperative for the remainder of the flight, when a failure is detected. In addition, it may be manually inhibited by switching off the TURB DAMP pushbutton on the overhead panel, when it is considered that comfort is degraded instead of being improved, and no failure is detected. It is only available if the following conditions are met: Aircraft in flight. Aircraft speed greater than 200 kt. Autopilot engaged or normal law active. Aircraft within the normal flight envelope.

Two exam points hide here:

1. An automatic failure is a one-shot loss. Once a failure is detected, the function is gone for the remainder of the flight — it does not come back even if the fault condition later clears. The associated ECAM is F/CTL TURB DAMP FAULT, with TURB DAMPER shown on the INOP SYS / STATUS page.
2. Manual inhibit is an escape hatch for one rare case. When the function is not failed but, in some turbulence, its correction is actually making the ride worse (a damping algorithm out of step with the real motion), FCOM lets you switch it off with the TURB DAMP pushbutton. The PRO-ABN note states the use plainly. Per FCOM PRO-ABN (F/CTL):

Note: When no alarm is given, but abnormal vibrations are present in non-turbulent conditions, this function may be disconnected via the TURB DAMP pb. Note the effect and report.

When you switch it off, a green memo appears. Per FCOM DSC-27-20-30:

TURB DAMP OFF: This memo appears in green, when the TURB DAMP pb is set to OFF.

4.2 Dispatch

Can you dispatch with turbulence damping inoperative? The MEL allows it. Dispatch with F/CTL TURB DAMP FAULT is covered by MEL item 27-93-04 (Turbulence Damping Function), which is Category C (installed 1, required 0 — may be inoperative); the TURB DAMP pushbutton OFF-light fault (item 27-01-05) is likewise Category C. In other words, losing turbulence damping is a retainable dispatch condition, not a no-go — which tells you exactly what it is: an optimisation for comfort and fatigue life, not a flight-safety necessity. Without it the aircraft flies just as safely, only with a less "ironed-out" ride in turbulence and a slightly higher fatigue tally.

What this means for you: if in turbulence you feel the aircraft "making its own small reverse corrections," that is the damping working — do not fight it. If you see TURB DAMP FAULT, do not worry: it will not return this flight, so action the MEL and report. And the TURB DAMP pushbutton is one you will almost never touch — it exists only for the rare "not failed but unhelpful" case.

5. ELAF — enhanced load alleviation, ailerons only

ELAF (Enhanced Load Alleviation Function) is a more recent layer. Like MLA it protects wing structural loads, but its surfaces are leaner and its triggers are completely different — read it as covering the cases MLA does not: the times the wing takes load without you deliberately pulling g. Per FCOM DSC-27-20-10-70:

The enhanced load alleviation function permits to alleviate the wing structure loads. The function is achieved through the upward deflection of the two pairs of ailerons only. The ELAF is activated: when airbrakes are extended, or In case of turbulence when load factor variation rate is excessive. The ELAF is available when the aircraft is in clean configuration and in Normal law. The ELAF orders are added to those generated by the normal law.

Compare it to MLA point by point — the design split falls out:

• "Two pairs of ailerons only" — no spoilers. The hardest difference from MLA (which borrows spoilers 4/5/6). Why does ELAF drop the spoilers? In both its triggers the spoilers are otherwise occupied or should not add drag: when the airbrakes are out, the spoilers are already doing the deceleration job; in pure turbulence, extra drag is unwelcome. So ELAF falls back to the "cheapest" surface — aileron up-deflection — to bleed outer-wing load. (The motive for dropping the spoilers is reasoning; the ailerons-only result is the manual fact.)
• Trigger 1 — airbrakes extended. Extending the airbrakes changes the wing's load distribution and amplifies certain loads in turbulence; ELAF up-deflects the ailerons to ease the wing.
• Trigger 2 — turbulence with excessive load-factor variation rate. Note it is the rate of change of load factor, not its magnitude. This is the complement to MLA: MLA watches "load factor > 2 g" (the magnitude of a sustained manoeuvre); ELAF watches "load factor changing too fast" (the transient spike of a gust).
• Normal Law + clean only. Stricter than MLA (which survives to Alternate Law) — ELAF is gone the moment you drop out of Normal Law.

[!warning]- MLA and ELAF are not two names for one function.

Both are "load alleviation," both deflect ailerons up, both need clean — so it is tempting to treat them as one thing. They are two independent functions targeting different load sources. MLA answers the pilot's deliberate high g (> 2 g, > 8° stick), uses ailerons + spoilers 4/5/6, and is available in Normal and Alternate Law. ELAF answers airbrake extension + gust transients (load-factor rate), uses ailerons only, and is available in Normal Law only. One is manoeuvre relief; the other is disturbance/configuration relief — complementary, non-overlapping.

6. Aileron droop and upfloat — making the surface "zero" match aerodynamic zero

Alongside MLA/ELAF, AMM lists two functions that continuously trim the ailerons in the background. They are worth fixing because the cruise-trim read-out in §7 rests on the same idea. Per AMM 27-90-00:

(7) Aileron droop This FCPC function consists in deflecting downwards the inboard and outboard ailerons, depending on the flap and slat position; it is engaged on the ground or in flight. When all the FCPCs are failed, the FCSCs ensure this function on the inboard ailerons only. (8) Aileron upfloat This FCPC logic is for any type of law, in flight and in clean configuration. To optimize performance, an offset is added to the servoed value of the servocontrol in order to have a real zero deflection in cruise. The offset value is +1.4° for inboard aileron and +1.4° for outboard aileron.

Aileron droop — the ailerons deflecting down with flaps/slats to act as "half a flap" for extra lift — is a high-lift behaviour; its detail belongs with the ailerons. The point here is aileron upfloat: in cruise the wing flexes under load, so an aileron sitting at its servo geometric zero is not at true aerodynamic zero. The system adds a +1.4° up-float offset to the servo command so the aileron reaches genuine zero-lift deflection in the cruise aerodynamic environment, minimising parasitic drag — a pure drag-trimming refinement. It is why "cruise trim" on this aircraft is not simply "surface parked at the geometric midpoint": the computers are quietly applying a fine zero-offset correction for you.

7. Aircraft trimming — the cruise rudder-trim yardstick

The last piece is not a function but a read-out standard: given a clean set of cruise premises, the rudder-trim indication should sit in a narrow band. Step outside it and something is usually asymmetric — lateral fuel imbalance, thrust asymmetry, or a rudder/trim problem. Per FCOM DSC-27-20-10-80:

When the aircraft is: In normal cruise range, In straight flight, With the autopilot engaged, With symmetrical engine thrust, and With fuel in the wing tanks distributed symmetrically, the rudder trim should stay between 1.9° right and 1.6° left.

All five premises must hold — drop any one (fuel imbalance, asymmetric thrust, hand-flying with yaw) and the yardstick no longer applies. Then comes the note most often overlooked and most worth understanding — the permanent offset. Per FCOM DSC-27-20-10-80:

Note: This indication corresponds to a true rudder deflection within ± 1°, taking into account the permanent offset of rudder trim indication when the aircraft is in cruise conditions (0.9° right, 0.6° left).

How to read the note: the band looks asymmetric and non-zero, which invites the question "why isn't it 0 and symmetric?" The answer is that the indication carries a built-in permanent offset (0.9° right / 0.6° left); subtract it and the true rudder deflection is only within ± 1° — essentially centred. This is the same thinking as the §6 aileron upfloat: the displayed/servoed "zero" is engineered, and what corresponds to it is the aerodynamic zero. So seeing the cruise rudder trim sitting off true-zero but inside that narrow window is completely normal — do not manually re-zero it. Conversely, if it clearly runs outside the window while all five premises hold, that is your cue to check lateral fuel balance and thrust symmetry.

The rudder-trim hardware itself (the RUD TRIM rotary, its slew rates, RESET, autopilot inhibit) is a yaw control input, covered with the pilot controls and the rudder; here we take only its "cruise-normal yardstick" face.

8. The four functions across a flight

1. Cruise, level, all normal — you do nothing. Aileron upfloat holds each aileron +1.4° up to trim the zero and save drag; the rudder trim sits inside the 1.9° R – 1.6° L window (true rudder within ± 1°); turbulence damping stands ready (> 200 kt, AP/Normal Law, inside the envelope — all met). This is what "normal trim" looks like.
2. Into a patch of moderate turbulence — turbulence damping takes the stage: the Nz accelerometer drives the elevator, the rear-bulkhead Ny accelerometer drives the rudder, micro-moving in anti-phase to suppress the structural vibration. If the load-factor variation rate is excessive, ELAF up-deflects the two aileron pairs to bleed the wing's transient load. Your stick feel is unchanged.
3. TCAS RA / gust avoidance, full aft stick — speed > 250 kt, clean, stick past 8°, load factor past 2 g, so MLA activates: ailerons up to +11° added, spoilers 4/5/6 up to +9° (growing with how far past 2 g you are), elevator compensating the nose-down moment. You keep every bit of the g you pulled; the outer wing is off-loaded; you feel nothing.
4. Steep descent, speedbrakes out — airbrake extension triggers ELAF (ailerons up). If you then haul full aft stick into MLA, MLA outranks the speedbrake: spoilers 1–3 retract to zero, 4–6 follow MLA.
5. F/CTL TURB DAMP FAULT — turbulence damping is inoperative for the rest of this flight; INOP SYS shows TURB DAMPER. Action the MEL (Category C, item 27-93-04) and report. The aircraft is still safe — just less "ironed" in turbulence, with a slightly higher fatigue tally.
6. Abnormal vibration with no warning, in non-turbulent air — per the PRO-ABN note you may deliberately switch the function off with the TURB DAMP pushbutton, observe whether the vibration clears, and report; the panel shows the green TURB DAMP OFF memo. This is the one rare time that pushbutton earns its keep.
7. Degrade to Alternate Law (multiple computer/sensor failures) — MLA stays (Alternate retains it); turbulence damping and ELAF are gone (Normal Law only). Degrade further to Direct Law and MLA goes too ("except in direct laws"). That exit order is the answer to the fifth self-test.

Self-test

[!note]- Q1. What load does MLA relieve, and how is "the demanded load factor is maintained" different from load-factor limitation?

MLA relieves outer-wing bending moment — by symmetrically up-deflecting the outer + inner ailerons and spoilers 4/5/6, it spoils outer-wing lift, drags the lift centre inboard, and lowers root bending, reducing the wing's design loads (FCOM DSC-27-20-10-40; AMM 27-90-00). It differs fundamentally from load-factor limitation: limitation caps the total g you can command; MLA leaves that total untouched — per FCOM, "the demanded load factor is maintained" — and only re-shapes the lift distribution inside the g you asked for. One bounds the total, the other reshapes it; the elevator compensation is what makes the total survivable.

[!note]- Q2. What are MLA's activation thresholds and availability conditions? Does it survive into Alternate and Direct Law?

Activation is AND'd: sidestick past 8° and load factor past 2 g. The ailerons add up to 11° up, spoilers 4/5/6 up to 9° (proportional to load factor in excess of 2 g), with simultaneous elevator compensation for the nose-down moment. Availability is three conditions: speed > 250 kt, FLAPS at 0 (clean), and Normal or Alternate Law (FCOM DSC-27-20-10-40). On degradation: MLA is retained in Alternate Law and lost only in Direct Law (AMM: "MLA (except in direct laws)").

[!note]- Q3. Which sensors and surfaces does turbulence damping use, and why does it touch no ailerons?

It uses the Nz accelerometer (longitudinal lane → elevator) and two dedicated Ny accelerometers (rear-bulkhead location, rear lateral lane → rudder / yaw damper); the PRIM add the damping command on top of the normal-law command (FCOM DSC-27-20-10-60; AMM 27-90-00). It touches no ailerons because it targets fuselage/tail structural modes (longitudinal bending, lateral tail sway) — the elevator and aft-fuselage rudder are the surfaces best placed to suppress those modes, and the Ny sensor sits at the rear bulkhead where lateral vibration amplitude is greatest. Availability: in flight, speed > 200 kt, autopilot engaged or Normal Law active, inside the normal envelope.

[!note]- Q4. After F/CTL TURB DAMP FAULT, does the function recover? When does the pilot switch it off deliberately? Is dispatch affected?

It does not recover — per FCOM it "becomes inoperative for the remainder of the flight," and stays out even if the fault clears. The pilot switches it off only in one special case: no failure, but abnormal vibration in non-turbulent air — disconnect via the TURB DAMP pushbutton, note the effect and report (FCOM PRO-ABN); the panel shows a green TURB DAMP OFF memo. Dispatch: MEL is Category C / retainable (item 27-93-04 for the function, 27-01-05 for the pushbutton light) — it is a comfort/fatigue optimisation, not a safety necessity.

[!note]- Q5. MLA and ELAF both up-deflect ailerons to relieve wing load — what actually separates them?

Three things: surfaces, trigger, and law. ELAF moves the two aileron pairs only — no spoilers; triggers on airbrake extension or excessive load-factor variation rate (the transient/gust, not the magnitude); available in Normal Law + clean only (FCOM DSC-27-20-10-70). MLA moves ailerons + spoilers 4/5/6; triggers on the pilot's deliberate high g (> 2 g and > 8° stick — the magnitude); available in Normal and Alternate Law. In one line: MLA handles the deliberate big manoeuvre, ELAF handles airbrake/gust transients — two independent, complementary functions.

[!note]- Q6. In cruise the rudder trim reads 1.5° right. Normal? Why does the manual mention a "permanent offset"?

Normal. The published normal window is 1.9° right to 1.6° left (premises: normal cruise range, straight flight, AP engaged, symmetrical thrust, symmetrical wing-tank fuel), and 1.5° right is inside it (FCOM DSC-27-20-10-80). The "permanent offset" means the cruise indication carries a fixed built-in offset (0.9° right / 0.6° left); subtract it and the true rudder deflection is only within ± 1° — essentially centred. So a rudder trim sitting off true-zero but inside that narrow window is an engineered-normal display — do not manually re-zero it; only if it clearly runs outside the window with all five premises holding should you check lateral fuel balance and thrust symmetry.

Key takeaways

These four functions are the part of Normal Law the pilot never feels and rarely thinks about — and that is exactly the point. They keep the wing and fin lighter-loaded and the airframe quieter, while your stick feel stays unchanged. The surfaces they borrow are enlarged in the ailerons, spoilers, and rudder articles; the full law-by-law degradation ladder is in Alternate Law and Direct Law.

References

Per FCOM DSC-27-20-10-40 (MLA — purpose / lift redistribution and bending moment; activation thresholds 8° and 2 g; aileron 11° and spoiler 9° deflection proportional to load factor; elevator compensation; availability > 250 kt / FLAPS 0 / normal or alternate; priority over speedbrakes). Per FCOM DSC-27-20-10-60 (Turbulence damping — purpose / structural modes; Nz and two Ny accelerometers; elevator and yaw damper; automatic inoperative-for-flight; manual TURB DAMP inhibit; availability conditions incl. > 200 kt). Per FCOM DSC-27-20-10-70 (ELAF — wing structure loads; two pairs of ailerons only; airbrakes-extended and load-factor-variation-rate triggers; Normal Law + clean). Per FCOM DSC-27-20-10-80 (Aircraft trimming — cruise rudder-trim band 1.9° right / 1.6° left; permanent-offset note, true rudder ± 1°). Per FCOM DSC-27-20-30 (green TURB DAMP OFF memo). Per FCOM PRO-ABN F/CTL (TURB DAMP FAULT — abnormal-vibration manual-disconnect note; INOP SYS TURB DAMPER). Per AMM 27-90-00 (FCPC functions — MLA clean-configuration activation and design-load reduction; MLA-over-speedbrake execution, spoilers 1–3 to zero / 4–6 to MLA; priority logic roll > droop > MLA > speedbraking, ground-spoiler override on landing; turbulence-damping two lanes and rear-bulkhead Ny accelerometer; aileron droop; aileron upfloat +1.4°; reconfiguration "MLA except in direct laws"; roll surfaces = ailerons + spoilers 2 thru 6 + rudder). Per MEL items 27-93-04 and 27-01-05 (turbulence-damping function and TURB DAMP pushbutton light, Category C dispatch). Reasoning flagged in-text (rear-bulkhead = largest lateral amplitude; ELAF dropping spoilers because they are otherwise occupied; upfloat-offset and rudder-trim-offset as one "engineered-zero" idea) is integrative synthesis, not verbatim manual statement.

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.