Hydraulic Warnings Reference

This article is a consolidated reference of the ECAM warnings and cautions that ATA 29 can produce. For each, it gives the trigger condition, the immediate procedural intent, and the expected cascade — what other indications appear alongside, and what each implies about system state.

It is not a substitute for the ECAM checklists, which are the authoritative procedural guidance. It is the cross-reference that lets a pilot, on seeing a specific warning, know what to expect and what other indications to look for.

1. Warning categories

ATA 29 produces warnings in five categories:

The order matters operationally: reservoir conditions are usually upstream causes; system pressure is the downstream consequence. A single reservoir condition often triggers multiple cascade warnings as the system responds.

Severity levels — L1 / L2 / L3

The A330 ECAM E/WD uses a three-level severity hierarchy (defined in ATA 31 FWC, applied throughout ATA 29):

The FCOM tags each warning header with its severity level explicitly — for example, HYD B ENG 1 PUMP LO PR is documented as L2, triggered when engine-pump pressure ≤ 1450 psi, and HYD G+Y SYS LO PR is L2, triggered when both Green and Yellow ≤ 1450 psi with reset at ≥ 1750 psi (the same 1450/1750 hysteresis introduced in General Description).

Two practical implications:

• No silent failures. If a hydraulic event is severe enough to need flight-crew intervention, it surfaces as an amber (or red) E/WD line with an aural cue. L1 events do not chime — they are present on the SD page or as a status line, and the crew picks them up during routine scan.
• L3 is rare on hydraulics. The A330 architecture distributes hydraulic work across three independent systems, so almost any single hydraulic event is one-system-affecting and amber-class. A red L3 hydraulic indication is essentially absent in the normal taxonomy — the dual-system combinations (G+B, G+Y, B+Y) are themselves still amber L2, with the procedural response carrying the implication ("LAND ASAP" appears as part of the procedure text, not as a separate red level).

2. Reservoir-side warnings

HYD G/B/Y RSVR LO LVL — reservoir low level

Combined-system trigger: When two reservoirs go low simultaneously (Green + Blue or Green + Yellow above 100 kt in flight), the HSMU also deploys the RAT automatically if not already deployed. This combined trigger is documented in Ram Air Turbine.

HYD G/B/Y RSVR OVHT — reservoir overheat

Diagnostic cross-check: A spurious OVHT from sensor failure produces an abrupt jump to 150 °C. A real OVHT shows gradual temperature rise. The diagnostic distinction matters for interpreting the FAULT lights that persist after pump shutdown.

HYD G/B/Y RSVR LO AIR PRESS — reservoir low air pressure

A transient LO AIR PRESS that clears within seconds is consistent with crossbleed delay. A persistent indication, especially combined with abnormal pump behaviour or system pressure fluctuation, indicates a genuine pump-inlet starvation risk.

3. System-pressure warnings

HYD G/B/Y SYS LO PR — system low pressure

SYS LO PR is distinct from PUMP LO PR. The pump-level warning indicates one specific pump has dropped; the system-level warning indicates the manifold pressure has dropped, regardless of which pumps caused it. On Green with two EDPs, a single PUMP LO PR does not produce SYS LO PR if the other EDP carries the system.

4. Pump-condition warnings

HYD G/B/Y PUMP LO PR — engine-driven pump low pressure

The light is inhibited on ground when engine is stopped — an EDP cannot maintain pressure if the engine driving it is not turning. The inhibit prevents nuisance FAULT illuminations during pre-engine-start operation.

HYD G/B/Y ELEC PUMP FAULT

5. RAT-specific indications

RAT FAULT

RAT OUT memo

Not a warning. Green normally, amber during takeoff phases 1 and 2 (when RAT should be stowed).

6. Combined warning recognition patterns

Certain warning combinations have specific operational implications:

The combined patterns are the diagnostic clues. A pilot recognising the pattern saves time during high-workload abnormal handling.

7. Memo lines — informational, not warnings

The memos do not require crew action. They confirm a state already commanded or triggered elsewhere. The crew uses them as situational awareness, not as items to act on.

8. The "what is real, what is sensor" question

Several warnings can be triggered by sensor failures as well as by real conditions. Recognising the difference is part of the diagnostic skill:

When in doubt, the procedure design assumes the worst case — execute the ECAM. Sensor failures will surface on the ground; in-flight, the procedure protects against the real-condition possibility.

9. The pilot's recognition sequence

For any unexpected ECAM caution:

1. Read the caution. Reservoir, system, or pump level?
2. Cross-check the SD HYD page. Does the indication match the cause-and-effect chain?
3. Recognise the cascade. What other warnings or memos appear alongside?
4. Identify the pattern. Is this a single-system loss, dual-system, sensor failure, or RAT-deployed configuration?
5. Execute the ECAM. The procedure is matched to the recognised pattern.
6. Determine the degraded profile. Approach, brake, gear, flap implications.

Each step uses the warnings reference above. The pattern-recognition habit develops with experience but starts with knowing what each warning means and what its cascade typically looks like.

10. Flight phase inhibition — the design philosophy

FCOM PRO-ABN-HYD adds a "Flight Phase Inhibition" line under most hydraulic warning entries. The line documents which flight phases will suppress E/WD display of that warning, even though the underlying trigger is still detected and latched by the HSMU.

What "inhibited" actually means

• The HSMU sensor still detects the condition (e.g., manifold pressure ≤ 1450 psi for SYS LO PR).
• The trigger is internally recorded.
• The E/WD line is suppressed from crew display during the inhibit window.
• When the aircraft transitions out of the inhibit phase, the warning re-emerges if the underlying condition is still present.

This is not "warning lost." It is warning postponed.

Why the architecture inhibits during specific phases

A330 ECAM divides each flight into ten phases (defined in ATA 31 FWC, not in ATA 29). The phases most relevant to hydraulic inhibition:

The phases that suppress hydraulic warnings (5, 6, 8, 9) share one operational characteristic: crew workload is at its peak and the time budget for handling a non-critical alert is essentially zero. A SYS LO PR caution that appears at V1 cannot be acted upon — the takeoff continues regardless. Displaying it would only distract from the rotation and initial climb.

The honest reasoning

Three design principles converge into the inhibit logic:

• Hydraulic faults are usually survivable for the inhibit window. Accumulators hold pressure for seconds-to-minutes. Dual-pump redundancy means most single-fault cases have an alternative supply path. A short delay before the crew sees the alert does not change the outcome.
• A red-level event would override the inhibit. Inhibition applies to amber L2 warnings, not to L3 (which the A330 hydraulic taxonomy essentially never produces — see severity table in §1).
• Re-emergence at phase change is automatic. The crew does not need to remember "check ECAM after gear-up" — the system itself re-presents the suppressed warning as soon as the aircraft passes out of the inhibit window.

Crew implication

Two consequences for crew awareness:

1. A clean E/WD during takeoff roll does not mean the system is healthy. It means no warning has triggered and propagated to display under the active phase logic. The "real" hydraulic state is what the SD HYD page shows post-rotation, after the phase 6 inhibit lifts.
2. A warning that appears at gear-up was likely already triggered during the roll. Treat its appearance as an existing condition newly visible, not a new condition newly developed. The implication for diagnostic reasoning: examine the SD HYD page state as if the condition had been present from before the takeoff.

The precise inhibit matrix (which phases inhibit which warnings) lives in ATA 31 FWC documentation, not ATA 29. The ATA 29 entries flag the principle and reference back; the FWC entries carry the table.

Self-test

[!note]- Q1. HYD G PUMP LO PR (1) appears, but HYD G SYS LO PR does not. The SD HYD page shows Green at the normal 3000 psi. What is the diagnosis?

Green EDP 1 has dropped offline (pump output below 120 bar trigger). Green EDP 2 is carrying the system on its own, so manifold pressure remains at 3000 psi. The single-pump failure is real but the system is operationally intact. The procedure calls for selecting ENG PUMP 1 OFF; the remaining EDP continues to provide Green pressure. The distinction between pump-level and system-level cautions is the diagnostic anchor: pump-level loss with normal system pressure = single pump down, redundancy carrying.

[!note]- Q2. HYD B RSVR LO LVL triggers in cruise. Per the procedure, both Blue pumps are selected OFF. The crew sees no LAND ASAP advisory. Is this correct?

Yes. The LAND ASAP advisory on a Blue (or Yellow) reservoir low level is conditional on Green being supplied by the RAT. With Green healthy (engines running, Green at 3000 psi via EDPs), the Blue loss is a single-system failure — manageable, with flight controls preserved on Green and Yellow. The aircraft continues to destination per normal abnormal procedures. The LAND ASAP would appear only in the combined Blue-lost + Green-on-RAT condition.

[!note]- Q3. All three reservoir LO AIR PRESS cautions trigger simultaneously, lasting about 20 seconds, then all three clear. System pressures remain stable at 3000 psi throughout. What happened?

A bleed-side transient affecting the common pressurisation source. Most likely an Engine 1 bleed transient with delayed crossbleed pickup; for ~20 seconds the reservoirs sat below the 1.5 bar relative threshold, triggering all three cautions. Then the crossbleed picked up, reservoir pressure recovered above 1.5 bar, and the cautions cleared. The system pressure staying stable at 3000 psi indicates the EDPs were still being fed adequately throughout — the cushion lost was not yet enough to produce cavitation. No further action is required, but the underlying bleed-side issue may warrant maintenance review.

[!note]- Q4. HYD G RSVR OVHT triggers. The crew switches both Green pumps OFF. The Green ELEC PUMP FAULT light extinguishes. The Green EDP 1 FAULT light stays on. The Green EDP 2 FAULT light also stays on. Is this correct?

Yes. The FAULT lights on the EDP pushbuttons stay illuminated after an overheat event for as long as the overheat condition persists, even after the pump is selected OFF. This is the FCOM-documented behaviour: the overheat is in the fluid, not in the pump, so switching off the pump does not clear the underlying condition. The ELEC PUMP FAULT light extinguished because Green ELEC PUMP was not the cause of the overheat (or because its FAULT trigger was a different condition that did clear with the pump OFF). The persistent EDP FAULT lights are normal indication of the active fluid temperature event.

[!note]- Q5. The HYD ELEC PUMP memo appears in green on the EWD. The Captain does not recall selecting any electric pump. What is the diagnosis?

One of the HSMU's automatic triggers has activated an electric pump. The memo does not identify which one. Common automatic triggers: Green ELEC PUMP for 25 seconds during gear retraction after an engine failure; Yellow ELEC PUMP after Engine 2 failure with flaps deployed; Blue ELEC PUMP under the combined Engine 1 failure plus PRIM 1/3 loss condition. The crew checks the SD HYD page to identify which pump is running and infers the underlying condition. The memo appearance itself is the trigger to investigate, not an item requiring direct action.

References

Per FCOM DSC-29-20 (all ECAM HYD indications and warnings); FCOM DSC-29-10-20 (HSMU automatic logic for reservoir-low-level cascades); FCOM PRO-ABN-HYD (procedural responses for all reservoir, system, and pump conditions); AMM 29-31 (sensor specifications determining warning thresholds and failure modes).

Independent study material, not an Airbus publication. Refer to current operator FCOM, FCTM, and QRH for operational use.