Elevators — Two Surfaces on the THS, Centering Mode, Green-First Reconfiguration

The two elevators are hinged on the THS and provide pitch control together with it: the elevators give the immediate pitch response, the THS carries the sustained trim. Each elevator has two electrohydraulic servo-controls with a third mode unique to pitch — centering — and a reconfiguration that runs green-hydraulic first.

Two elevators are hinged on the Trimmable Horizontal Stabilizer (THS); in conjunction with the THS, they ensure the pitch control... Two electrohydraulic servocontrols actuate each elevator. — AMM 27-30-00

1. Layout and the elevator–THS pairing

Per AMM 27-30-00, the two elevators are hinged on the THS and ensure pitch control in conjunction with it. Each elevator is driven by two electrohydraulic servo-controls; a position transducer beside the servos reports elevator position to the FCPC and FCSC and to the SD via the FCDC. In manual flight the sidesticks signal the computers, which drive the servos per the control laws.

[!note]- Elevators handle the moment, the THS handles the trim (integrative synthesis) Pitch is a two-element system: the elevators give the fast pitch response to a stick input, while the auto-trim continuously moves the THS to offload the elevators back toward neutral. That is why a steady manoeuvre leaves the elevators near centred with the THS carrying the load — and why losing the elevators (red MAN PITCH TRIM ONLY) leaves pitch on the THS trim wheel alone.

2. The three servo modes — including centering

Per FCOM DSC-27-10-20, each elevator's two servojacks have three modes: active, damping, centering. In normal operation one is active and one damping (a second goes active for some manoeuvres); on an active-jack failure the damped one becomes active. The endpoints:

• neither jack controlled electrically nor hydraulically → both damping;
• none of the four elevator jacks controlled electrically → all four centering (hydraulically held neutral).

[!warning]- Centering is the elevator-only endpoint — it holds neutral, it doesn't float Unlike ailerons/spoilers, the elevators have a centering mode: if all four jacks lose electrical control, they are hydraulically held at neutral rather than damped (FCOM DSC-27-10-20). A floating elevator at neutral is safer for pitch than one drifting with the airflow — so the pitch surface fails to a held centre, not a free-floating damp. (Damping is still the fallback when hydraulic pressure is also lost.)

3. Green-first reconfiguration and ground droop

Per FCOM DSC-27-10-20, elevator control runs green-hydraulic first: PRIM 1 on the green jacks → PRIM 2 on the blue/yellow jacks → SEC 1, and with all PRIMs lost SEC 1 still flies the elevators while the THS reverts to the manual trim wheel. On the ground with hydraulics unpressurised, the normal elevator position is drooped down to the servo-control stop (AMM 27-30-00) — expected, not a fault.

[!note]- The green-first order ties pitch to the master-computer logic (integrative synthesis) Because PRIM 1 drives the elevators on green jacks, losing green hydraulics both shifts the elevators to PRIM 2 (blue/yellow) and makes P2 the master computer (01) — one hydraulic event, two coupled consequences. The blue/yellow split across the remaining jacks is why a single further hydraulic loss still leaves an elevator driven.

4. Counterintuitive points

[!warning]- Elevators fail to centering (held neutral), not to free damping Loss of electrical control of all four jacks → centering; damping only when hydraulic pressure is also gone (FCOM DSC-27-10-20).

[!warning]- Ground elevators droop down — that is normal Unpressurised, the elevators rest drooped at the servo stop (AMM 27-30-00).

Self-test

[!note]- Q1. How many elevators, where hinged, and how do they relate to the THS? Two, hinged on the THS; elevators give immediate pitch, THS carries sustained trim (auto-trim).

[!note]- Q2. The three elevator servo modes, and the all-jacks-lost endpoint? Active / damping / centering; with no electrical control of all four jacks → all centering (hydraulically held neutral).

[!note]- Q3. The elevator reconfiguration order? PRIM 1 (green) → PRIM 2 (blue/yellow) → SEC 1; green-hydraulic loss also makes P2 master.

[!note]- Q4. Normal ground elevator position unpressurised? Drooped down to the servo-control stop (normal).

Key takeaways

References

• AMM 27-30-00 (Elevator — Description and Operation) — two elevators hinged on the THS, pitch control in conjunction with the THS; two electrohydraulic servo-controls per elevator; position transducer to FCPC/FCSC, SD via FCDC; manual control from sidesticks per control laws; ground unpressurised normal position drooped to servo-control stop.
• FCOM DSC-27-10-20 / AMM 27-34-00 — each elevator two servojacks with active/damping/centering modes (one active/one damping, second active on some manoeuvres, active fail → damped active, neither electrical nor hydraulic → damping, no electrical control of four jacks → centering); pitch reconfiguration PRIM 1 (green jacks) → PRIM 2 (blue/yellow) → SEC 1, all PRIM lost → SEC 1 elevator + THS manual trim wheel.

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.