Load Alleviation — MLA, ELAF, Turbulence Damping and Trimming

Normal law runs four automatic functions the pilot never commands but should understand: MLA and ELAF relieve wing structural loads, turbulence damping improves ride and damps structural modes, and the trimming reference sets the cruise rudder-trim band. These are the "behind-the-scenes" half of Normal law's manoeuvre-load-alleviation promise.

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. — FCOM DSC-27-20-10-40

1. MLA — Manoeuvre Load Alleviation

Per FCOM DSC-27-20-10-40, MLA redistributes lift inboard to cut the wing bending moment on the outer wing during high-g manoeuvres — while maintaining the demanded load factor (the pilot still gets the g). It uses spoilers 4, 5, 6 and the ailerons, becoming active when the sidestick is pulled more than 8° and load factor exceeds 2 g:

• ailerons symmetrically up — max 11° added to any roll demand;
• spoilers 4/5/6 symmetrically up — max 9° added, deflection proportional to load factor above 2 g;
• an elevator demand is applied simultaneously to cancel the pitching moment from the spoilers/ailerons.

Available only when speed > 250 kt, FLAPS lever 0, in normal or alternate law. MLA has priority over the speedbrakes.

[!warning]- MLA moves lift inboard without changing the g you feel The clever part: MLA raises ailerons and outboard spoilers to shed lift from the outer wing (cutting the bending moment that sizes the wing structure), then adds elevator to keep the commanded load factor (FCOM DSC-27-20-10-40). The pilot's 2.5 g pull still produces 2.5 g — the load is just carried more inboard. Because it borrows the same surfaces as roll, MLA adds to roll demand (11°/9° caps) and outranks the speedbrakes. Note it works in normal and alternate law.

2. ELAF — Enhanced Load Alleviation Function

Per FCOM DSC-27-20-10-70, ELAF also relieves wing structural loads, but through the two pairs of ailerons only (upward). It activates when airbrakes are extended, or in turbulence when the load-factor variation rate is excessive, and is available in clean configuration, Normal law only; its orders add to the normal-law command.

[!note]- ELAF vs MLA — ailerons-only, turbulence-and-airbrake triggered (integrative synthesis) The two load-relief functions overlap but differ: MLA uses spoilers 4/5/6 + ailerons on a manoeuvre (>8° stick, >2 g, >250 kt, normal/alternate); ELAF uses ailerons only on airbrakes-out or excessive turbulence load-rate, Normal law only (FCOM DSC-27-20-10-40/70). MLA targets the deliberate high-g pull; ELAF targets gust/airbrake transients. Both shed outer-wing lift to protect the structure.

3. Turbulence damping — using the EFCS's own accelerometers

Per FCOM DSC-27-20-10-60, the turbulence damping function damps the structural modes induced by atmospheric turbulence. It uses the Nz accelerometer and two dedicated Ny accelerometers; the PRIMs compute a damping command added to the normal-law command for the elevator and the yaw damper. Available in flight, speed > 200 kt, AP engaged or normal law active, within the normal envelope. It is auto-monitored and becomes inoperative for the rest of the flight on a detected failure, and can be manually inhibited via the TURB DAMP pushbutton if it is degrading rather than improving comfort.

[!note]- This is what the EFCS Nz/Ny accelerometers are for (integrative synthesis) Recall the dedicated Nz/Ny accelerometers in the EFCS input suite — here is their primary job: the PRIMs read structural accelerations and add a damping command to the elevator and yaw damper to quell turbulence-induced structural modes (FCOM DSC-27-20-10-60). The same Nz accelerometers also back up load-factor sensing if the ADIRUs fail — one sensor set, two roles.

4. Aircraft trimming — the cruise rudder-trim reference

Per FCOM DSC-27-20-10-80, in normal cruise, straight flight, AP engaged, symmetric thrust and symmetric wing fuel, the rudder trim should stay between 1.9° right and 1.6° left. This corresponds to a true rudder deflection within ±1°, allowing for the permanent offset of the rudder-trim indication in cruise (0.9° right, 0.6° left).

[!note]- A small built-in rudder-trim offset is normal in cruise The indication is not symmetric about zero — there is a permanent cruise offset (0.9° R / 0.6° L) baked into the display (FCOM DSC-27-20-10-80). A rudder trim reading slightly off-centre in cruise is expected, not a fault.

5. Counterintuitive points

[!warning]- MLA keeps your g while relieving the wing — and outranks speedbrakes Lift moves inboard, elevator preserves the commanded load factor, and MLA has priority over the speedbrakes (FCOM DSC-27-20-10-40).

[!warning]- Turbulence damping can be switched off If the TURB DAMP function degrades comfort (and no failure exists), the crew can inhibit it with the overhead pushbutton (FCOM DSC-27-20-10-60).

Self-test

[!note]- Q1. What does MLA do, with which surfaces, and under what conditions? Redistributes lift inboard to cut wing bending moment (load factor maintained), using spoilers 4/5/6 + ailerons up + elevator compensation; active at >8° stick, >2 g, >250 kt, flaps 0, normal/alternate law; priority over speedbrakes.

[!note]- Q2. How does ELAF differ from MLA? Ailerons only, triggered by airbrakes extended or excessive turbulence load-rate, Normal law only, clean config.

[!note]- Q3. What sensors does turbulence damping use, and what can disable it? The EFCS Nz + two Ny accelerometers; auto-off on failure, or manual TURB DAMP pb; needs > 200 kt, AP or normal law, in envelope.

[!note]- Q4. The cruise rudder-trim band, and why off-centre is normal? 1.9° R to 1.6° L; a permanent indication offset (0.9° R / 0.6° L) makes a slightly off-centre reading normal.

Key takeaways

References

• FCOM DSC-27-20-10-40 (Normal Law — MLA) — redistributes lift inboard to relieve outer-wing bending moment, demanded load factor maintained; spoilers 4/5/6 + ailerons (ailerons up max 11° added to roll, spoilers up max 9° proportional to load factor above 2 g, elevator compensates pitching moment); active >8° stick and >2 g; available >250 kt, flaps 0, normal/alternate law; priority over speedbrakes.
• FCOM DSC-27-20-10-70 (Normal Law — ELAF) — wing-load relief via two pairs of ailerons up only; activates with airbrakes extended or excessive turbulence load-factor rate; clean config, Normal law only; added to normal-law orders.
• FCOM DSC-27-20-10-60 (Normal Law — Turbulence Damping) — damps turbulence-induced structural modes using Nz + two dedicated Ny accelerometers, PRIM command added to elevator + yaw damper; in flight, >200 kt, AP or normal law, within envelope; auto-inoperative on failure for rest of flight, manual TURB DAMP pb inhibit.
• FCOM DSC-27-20-10-80 (Normal Law — Aircraft Trimming) — cruise rudder trim 1.9° right to 1.6° left in straight flight/AP/symmetric thrust and fuel; true deflection within ±1°, permanent indication offset 0.9° right/0.6° left.

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.