Thrust Reverser — Four Blocker Doors, Deployment Interlock, AUTO RESTOW

The overview noted reverse is driven by aircraft hydraulics. This article opens the reverser: how the blocker doors deflect the bypass stream, what interlocks deployment, how thrust scales with deploy fraction, and how an inadvertent unstow is self-protected. It is the basis for reverser faults, landing deceleration and the hydraulic coupling.

1. Structure and drive

The aircraft performs engine reverse thrust via four pivoting blocker doors on each engine to create a deflected fan airstream. A hydraulic door jack positions each door. ‐ The blue circuit powers the doors on engine 1 ‐ The yellow circuit powers the doors on engine 2. The thrust reverser system is independently controlled for each [engine].

Per DSC-70-70: four pivoting blocker doors per engine deflect the bypass fan stream, each positioned by a hydraulic door jack; the blue circuit drives engine 1, the yellow circuit drives engine 2, each engine controlled independently.

2. Stowed vs deployed

Per the fan-reverser-operation diagram:

 STOWED:   blocker doors flush with the cowl; AIR FLOW straight aft → forward thrust
           hydraulic actuator retracted
 DEPLOYED: blocker doors pivot out, block the bypass duct; AIR FLOW deflected forward → reverse thrust
           hydraulic actuator extended

Reverse is not "spinning the fan backwards" — the blocker doors block and deflect the bypass stream forward (the bypass air, echoing the single large fan carrying most of the flow).

3. Deployment interlock — three conditions

Deployment requires : ‐ TLA reverse signals from FADEC and from the flight control primary computer (PRIM 1 or PRIM 3) ‐ One FADEC channel that operates with its associated throttle reverse signal ‐ Aircraft on ground signal from at least one LGCIU.

Per DSC-70-70, deployment needs all three: TLA reverse from the FADEC and a flight-control primary computer (PRIM 1 or 3); one FADEC channel with its throttle reverse signal; and an on-ground signal from at least one LGCIU (LGCIU 1 preferred if valid).

[!warning]- The interlock is the defence against inadvertent in-flight deployment None of the three is optional: the flight-control PRIM must also give a reverse signal (not just the FADEC), and an LGCIU must report on-ground. Without an on-ground signal, the reverser cannot deploy — the core of the safety interlock, an in-flight deployment being catastrophic.

4. Deploy fraction and thrust (70% / 90%)

During deployment, engine reverse thrust is limited to idle, until the reversers are deployed by more than 70 %. Then, FADEC will command full reverse thrust to be available when reversers position are more than 90 % deployed.

Per DSC-70-70:

This prevents large reverse thrust before the doors are positioned and the deflected stream established.

5. AUTO RESTOW and idle protection

The FADEC will automatically command the engine to idle and the reverser to stow if at least one door is unstowed by more than 5 % and reverse thrust is not selected while engine is running. The affected reverser will remain pressurized after affected door is locked back. If the door is still detected unstowed, the engine will remain at idle for the remainder of the flight.

Per DSC-70-70, if a door is unstowed by more than 5 % with reverse not selected while the engine runs, the FADEC commands idle + stow; the reverser stays pressurised after the door locks back; if the door still reads unstowed, the engine stays at idle for the rest of the flight.

[!warning]- A 5 % unstow can lock the engine at idle for the whole flight Not a fully open door — one door unstowed > 5 % with reverse not selected → idle + stow (DSC-70-70). If it still reads unstowed, that engine stays at idle for the remainder of the flight (unrecoverable) — the serious consequence of an inadvertent unstow, the subject of Reverser Faults.

6. Interfaces and counterintuitive points

[!warning]- Reverse is driven by aircraft hydraulics (blue 1 / yellow 2), not the engine Blue drives engine 1's reverse, yellow drives engine 2's (DSC-70-70) — a hydraulic system failure affects that engine's reverser. An ATA 70 ↔ ATA 29 coupling.

[!warning]- < 70 % gives idle, > 90 % gives full reverse Not "select reverse → full reverse instantly" — with the doors not positioned (< 70 %) only idle, and > 90 % for full reverse (DSC-70-70).

Self-test

[!note]- Q1. What produces reverse, how many doors, and what drives them? Four pivoting blocker doors per engine deflect the bypass stream; hydraulic door jacks, blue circuit engine 1, yellow circuit engine 2, independently controlled.

[!note]- Q2. The three deployment conditions? ① TLA reverse from FADEC + PRIM 1/3; ② one FADEC channel with its throttle reverse signal; ③ on-ground from at least one LGCIU.

[!note]- Q3. Deploy fraction vs thrust? < 70 % idle; > 90 % full reverse.

[!note]- Q4. What protects against an unstowed door? Door unstowed > 5 % with reverse not selected while running → FADEC idle + stow; if still unstowed, idle for the rest of the flight.

[!note]- Q5. Which hydraulic system drives each engine's reverse? Engine 1 = blue, engine 2 = yellow.

Key takeaways

References

• FCOM DSC-70-70 — four blocker doors, blue/yellow hydraulics, deployment interlock (FADEC + PRIM + LGCIU), < 70 % idle / > 90 % full, AUTO RESTOW (unstow > 5 %), LGCIU 1 preferred.
• AMM 78-00-00 — EXHAUST: thrust reverser + common nozzle assembly.
• Fan-reverser-operation diagram — stowed (straight aft, forward thrust) vs deployed (deflected forward, reverse).

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.