ECAM HYD Page Reading

The SD HYD page is the pilot's primary diagnostic surface for the hydraulic system. It is auto-displayed on any hydraulic ECAM event and can be called manually via the ECAM control panel. Every element on it is documented; reading the page well means knowing what each symbol, colour, and value indicates — and what their combinations mean.

This article walks through the page systematically. The cockpit interface (overhead 29 panel pushbuttons) is covered in Hydraulic Generation Overview and the individual pump articles. The page itself is treated here as the consolidated read of system state.

1. The page layout

                    ┌──────────────────────────────────────────────────┐
                    │              HYD                                  │
                    │                                                   │
                    │   ┌─ GREEN ──┐  ┌─ BLUE ──┐  ┌─ YELLOW ──┐       │
                    │   │          │  │          │  │           │       │
                    │   │ Quantity │  │ Quantity│  │ Quantity   │       │
                    │   │   bar    │  │   bar   │  │   bar      │       │
                    │   │   (n)    │  │   (n)   │  │   (n)      │       │
                    │   │          │  │          │  │           │       │
                    │   │ OVHT     │  │ OVHT    │  │ OVHT       │       │
                    │   │ LO AIR   │  │ LO AIR  │  │ LO AIR     │       │
                    │   │  PRESS   │  │  PRESS  │  │  PRESS     │       │
                    │   │          │  │          │  │           │       │
                    │   │ FIRE SHUT│  │ FIRE    │  │ FIRE       │       │
                    │   │ OFF VLV  │  │ SHUT-OFF│  │ SHUT-OFF   │       │
                    │   │   (2)    │  │  (1)    │  │  (1)       │       │
                    │   │          │  │          │  │           │       │
                    │   │ ENG PUMP │  │ ENG PUMP│  │ ENG PUMP   │       │
                    │   │ G1 G2    │  │   B     │  │   Y        │       │
                    │   │          │  │          │  │           │       │
                    │   │ ELEC     │  │ ELEC    │  │ ELEC       │       │
                    │   │ PUMP     │  │  PUMP   │  │  PUMP      │       │
                    │   │          │  │          │  │           │       │
                    │   │ LEAK     │  │ LEAK    │  │ LEAK       │       │
                    │   │  MEAS    │  │  MEAS   │  │  MEAS      │       │
                    │   │  VALVE   │  │  VALVE  │  │  VALVE     │       │
                    │   │          │  │          │  │           │       │
                    │   │  System  │  │ System  │  │ System     │       │
                    │   │  pressure│  │ pressure│  │ pressure   │       │
                    │   │          │  │          │  │           │       │
                    │   └──────────┘  └──────────┘  └───────────┘       │
                    └──────────────────────────────────────────────────┘

Each column shows one hydraulic system. Within each column, indications stack vertically with reservoir-side information at the top and pump/distribution-side at the bottom. The structure is symmetric across the three columns — what you learn for Green applies to Blue and Yellow with adjustments for their consumer specifics.

2. Reservoir indications (top of each column)

Quantity

The reservoir quantity indication shows the temperature-corrected fluid level in the reservoir.

A white quantity is the architecture's notification that the temperature transmitter (2JS1/2/3 on the reservoir return port) has lost continuity. The numerical reading is still shown, but it is now a raw value, not corrected for fluid expansion with temperature. The crew interprets it with that knowledge and watches for actual quantity changes.

LO AIR PRESS

LO AIR PRESS triggers when the gas cushion (normally 4.5 bar absolute / 3.5 bar relative) drops below 1.5 bar relative — i.e., roughly two-thirds of the normal cushion has been lost. Causes include Engine 1 bleed transients with delayed crossbleed pickup, complete bleed-source loss, or a leak in the reservoir's own pressurisation interface.

OVHT

OVHT triggers when the platinum-resistance temperature sensor (2JS1/2/3) detects rising fluid temperature above the threshold. A sensor failure that produces a 150 °C reading also generates the OVHT — the fail-safe default. Diagnostic cross-check: a real OVHT shows a gradual temperature rise; a sensor failure shows an abrupt jump to the default value.

3. Fire shut-off valve indications (per pump)

The fire shut-off valve on each EDP shows as a small symbol in each column. For Green, two symbols are shown (one for each EDP); Blue and Yellow show one each.

The Green fire shut-off valves may close automatically via the HSMU on a Green reservoir low level; Blue and Yellow only close on ENG FIRE pushbutton press. The 150-second reopen on Green appears here as the symbols changing from cross-line amber back to in-line green about 2.5 minutes after the initial closure.

FCOM wording note — "in line green = partially closed"

A close reading of FCOM DSC-29-20 reveals slightly unintuitive wording on the fire shut-off valve symbology: the manual describes the in-line green state literally as "the valve is partially closed", not "fully open". Crews encountering this for the first time often pause — does in-line green mean the valve is open or closed?

The intended meaning is operationally open (fluid flows through). The "partially closed" phrasing reflects the valve's mechanical reality: a 90° ball valve at rest in the open position has its ball oriented so flow passes through, but the ball itself is still physically present in the line and partially obstructs the bore compared with a straight pipe. The phrasing is engineering-precise but reads oddly against the in-cockpit interpretation.

For the crew, the pragmatic reading is:

The FCOM's literal wording rewards careful reading; the operational interpretation matches what the crew expects. The two are not in conflict, but the wording is a documented small-trap for early ATA-29 study.

4. ENG PUMP indications

The pump identification letter (G1, G2, B, Y) appears next to the symbol. The letter is white in normal operation; it becomes amber when the corresponding engine's N3 is below idle — the architecture's hint that the engine itself is not producing the rotation needed to drive the EDP.

The LO annunciation is pump-specific, not system-wide. On Green with two EDPs, LO on one EDP can occur while the system as a whole remains pressurised by the other EDP. This is the key distinction between PUMP LO PR and SYS LO PR (covered in Pump Failure vs System Failure).

5. ELEC PUMP indications

The ELEC PUMP indication has different colour conventions from the ENG PUMP. The white "normal" state covers both off and on-with-pressure conditions; the amber state catches both supply faults and pump-side faults. Disambiguation between the two is by cross-reference to the system pressure (if green and at expected value, the pump is producing pressure; if pressure is dropped, the pump is failing).

For Green and Yellow, the ELEC PUMP runs automatically per the HSMU triggers (Green System Pumps section). The HYD ELEC PUMP MEMO on the EWD indicates that at least one electric pump is running — the SD HYD page is where the crew identifies which specific pump.

6. Leak measurement valve indications

In flight, all three leak measurement valves are forced open by the HSMU inhibit. The closed indication in flight (if it ever appeared) would be a malfunction — but the architecture's inhibit makes this case essentially impossible.

On the ground during cargo-door operation, the Yellow leak measurement valve closes to isolate Yellow primary flight controls. This is normal architecture, not a fault.

7. System pressure indication

At the bottom of each column, a numeric pressure reading shows the system manifold pressure.

The pressure value is what tells the crew whether the system is operationally available. A value at the normal band indicates the pumps are maintaining pressure successfully. A value at 2500 psi on Green (with the RAT OUT memo) is the RAT-supplied configuration. A value below 1450 psi indicates the system is unpressurised and the corresponding consumers are unavailable.

8. The reading sequence

A useful pattern for reading the SD HYD page systematically:

1. Top down: reservoir quantity (any amber?), LO AIR PRESS (any amber?), OVHT (any amber?). This identifies reservoir-side conditions.
2. Middle: fire shut-off valves (any cross-line amber?). This identifies isolation events.
3. Below middle: pump states. ENG PUMP cross-line amber means pump off; LO means pump producing inadequate pressure. ELEC PUMP amber means pump fault.
4. Bottom: system pressure. Normal band, RAT band, or below SYS LO PR threshold.

The top-down sequence matches the architecture's logical flow: fluid stock first, then bleed/temperature integrity, then pump-source integrity, then system-output integrity.

9. Reading combinations — what they mean

Some combinations are more informative than any single indication. Examples:

The cross-checks form the basis of diagnostic decisions during abnormal procedures.

10. Reading after RAT extension

A specific recognition pattern: after RAT extension on Green (dual engine failure or dual-system reservoir low), the SD HYD page shows:

• Green quantity: green (normal — RAT does not drain the reservoir abnormally)
• Green fire shut-off valves: depends on whether HSMU automatic closure has occurred
• Green ENG PUMP: both cross-line amber (engines are not running, so EDPs are off)
• Green ELEC PUMP: white if not selected on
• Green system pressure: 2500 psi (RAT-regulated)

Combined with the RAT OUT memo on the EWD, this is the recognised configuration for RAT-supplied Green. The crew accepts the configuration and continues per the appropriate abnormal procedure.

11. The 13 fields — precise reference

The ECAM HYD page is organised into 13 documented fields per maintenance documentation. Each field has a specific identifier, source, and interpretation. The numbering matches AMM documentation conventions:

Field-by-field interpretation

Field 1 — Reservoir quantity

• Green: temperature-corrected value displayed.
• White: temperature transmitter input lost; raw value shown (still usable but uncompensated).
• Amber: quantity below warning threshold (LO LEVEL detected by reed switch 10JS).

Field 2 — Reservoir LO AIR PRESS

• Not annunciated: cushion above 1.5 bar relative.
• Amber: cushion ≤ 1.5 bar relative (trigger).
• Returns to normal at ≥ 1.7 bar relative (hysteresis).

Field 3 — Reservoir OVHT

• Not annunciated: temperature normal.
• Amber: fluid temperature ≥ 95 °C ± 2 °C, rising trend (real OVHT) or sensor lost (HSMU defaults to 150 °C).

Field 4 — Fire shut-off valve

• In-line green: valve fully open.
• In-line green (partial): transient during 1.8-second travel.
• Cross-line amber: valve fully closed (ENG FIRE pushbutton or Green automatic HSMU closure).

Field 5 — ENG PUMP indication

• In-line green: pushbutton ON, pump producing pressure above 120 ± 5 bar.
• Cross-line amber: pushbutton OFF.
• LO amber: pushbutton ON, pump output below 120 ± 5 bar (pump-output pressure switch triggered).

Field 6 — PUMP identification (G1 / G2 / B / Y)

• White: normal — corresponding engine N3 at or above idle.
• Amber: corresponding engine N3 below idle — pump cannot maintain pressure even if commanded on. The colour change is an early-warning for engine-state-related pump conditions.

Field 7 — ELEC indication

• White: normal (off, or on with normal output).
• Amber: AC power supply failed, OR pump commanded on but not producing pressure.

Field 8 — ELEC PUMP control (4 states)

• AUTO: HSMU controls per automatic triggers.
• ON: pump commanded on by crew.
• OFF: pump inhibited.
• FAULT: amber FAULT light illuminated.

Field 9 — ELEC PUMP OVHT

• Annunciation when the internal motor temperature switch (193 °C ± 5 for Vickers, 200 °C ± 10 for Parker) triggers. Latches until cooling + ground circuit-breaker reset.

Field 10 — System label

• Green identifier with normal pressure.
• Amber identifier when SYS LO PR triggers (system pressure ≤ 1450 psi, decreasing).
• Returns to green when pressure recovers above 1750 psi (300 psi hysteresis).

Field 11 — System pressure (numeric)

• Numeric reading from transducer 6JS. Conversion: bar = (V − 1) × 50, so 100 bar = 3 V, 200 bar ≈ 5 V (saturating).
• Displayed values: ~3000 psi (normal), ~2500 psi (Green on RAT), below 1450 psi (SYS LO PR active).

Field 12 — RAT control (4 states)

• Stowed and normal: no annunciation, no abnormal state.
• Deployed but no flow: RAT extending or in startup.
• Deployed with flow: RAT supplying Green at 2500 psi.
• Fault: RAT system fault (one of several configurations).

Field 13 — RPM indication (RAT)

• Numeric or graphical indication of turbine RPM.
• Normal range: 4850–6370 RPM (governor-regulated).
• Out-of-range: governor fault or transient startup.

12. The 30-second scan pattern — refined

The architecture of the page supports a systematic scan, refined here per the field structure:

Step 1 (5 sec) — Reservoir line (top)
   ▸ All three quantities green / numerical values in band? (Fields 1)
   ▸ Any LO AIR PRESS amber? (Fields 2)
   ▸ Any OVHT amber? (Fields 3)
   ▸ Any quantity in white? (Sensor issue, not LO LEVEL)

Step 2 (5 sec) — Fire shut-off valves
   ▸ All in-line green? (Field 4)
   ▸ Any cross-line amber? → Check `ENG FIRE` pushbutton state

Step 3 (5 sec) — Pump rows
   ▸ All ENG PUMP indicators in-line green? (Field 5)
   ▸ Any `LO` amber? → single pump fault → cross-check with system pressure
   ▸ Any PUMP identifier amber? (Field 6) → corresponding engine N3 low — informational
   ▸ ELEC PUMP indicators white? (Field 7)
   ▸ Any ELEC PUMP amber? (AC supply or pump-not-producing fault)

Step 4 (5 sec) — System pressure (bottom)
   ▸ Three pressure values normal? (Field 11)
   ▸ Green = 3000 psi normally, ~2500 psi if on RAT
   ▸ System label colour normal? (Field 10)

Step 5 (5 sec) — RAT area
   ▸ RAT in stowed state, no annunciation?
   ▸ If deployed: check Field 12 (state) + Field 13 (RPM)

Step 6 (5 sec) — Combinations
   ▸ Any combination patterns (e.g., quantity amber + FSOV cross-line amber → reservoir LO LVL with HSMU automatic closure)?

The 30-second scan is the routine cockpit-monitoring pattern; on an actual ECAM event, the page auto-displays and the abnormal procedure drives further investigation.

13. Colour-coding semantic rules — unified summary

Across all fields, the page follows consistent colour semantics:

The semantic anchor: amber means "the architecture's automatic monitoring has noticed something". Green and white are routine; amber is a marker requiring crew interpretation against the procedural framework. The ECAM caution that accompanies any amber HYD page indication provides the procedural anchor.

14. Time-sequence tracking

ECAM HYD page indications change over time during abnormal events. Recognising the sequence patterns helps the crew interpret what is happening:

The crew uses the sequence as part of the diagnostic process — for example, an OVHT amber that appears together with quantity going white is more consistent with sensor failure than with a real fluid overheat (because both share the same temperature-transmitter signal source).

Self-test

[!note]- Q1. The SD HYD page shows Blue quantity in green at the normal value, Blue OVHT not annunciated, Blue ENG PUMP cross-line amber, Blue ELEC PUMP white, Blue system pressure at the normal 3000 psi. What is the configuration?

Blue's EDP has been switched off by the crew (cross-line amber on ENG PUMP), but Blue system pressure remains at 3000 psi. This is only possible if the ELEC PUMP is supplying pressure — but the ELEC PUMP indication is white. The configuration is unusual and worth examining: if the ELEC PUMP is running successfully and producing pressure, the indication should reflect that. White typically means "off" or "on with pressure normal" — the latter is consistent with the system pressure reading. Most likely interpretation: the crew has selected Blue ELEC PUMP ON manually, it is producing normal pressure, and the indication colour reflects "commanded on with normal output." This is a non-default but architectural state.

[!note]- Q2. The SD HYD page shows Green quantity in amber, Green fire shut-off valves both cross-line amber, Green ENG PUMP G1 and G2 both showing LO in amber, Green system pressure at 2500 psi. What is happening?

Multiple things at once, in a recognisable pattern: Green reservoir is at low level (quantity amber); the HSMU has automatically closed both Green fire shut-off valves (cross-line amber); the EDPs are showing low output pressure (LO); but the system is pressurised at 2500 psi. The 2500 psi figure is the RAT regulator output — the RAT is supplying Green via its own independent path (which bypasses the fire shut-off valves). This is the dual-engine-failure scenario with Green on RAT, with the HSMU's automatic low-level closure also executed (perhaps a leak triggered the reservoir low level). The crew is committed to the RAT configuration for the remainder of the flight.

[!note]- Q3. The Yellow quantity indication is white instead of green. The numerical value is in the normal range. Action required?

The temperature transmitter or its wiring has lost continuity. The displayed value is no longer corrected for fluid temperature. The numerical reading is still trustworthy as an uncompensated raw measurement; in normal operating temperatures the difference between corrected and uncorrected is modest (a few percent), so the value being in the normal range is genuinely useful information. The crew action is awareness — interpret the value as uncorrected, monitor for any actual quantity changes (which would still trigger appropriate cautions if a threshold is crossed), and report the temperature-side issue for ground maintenance. No immediate hydraulic action required.

[!note]- Q4. The Green fire shut-off valves close automatically on a Green reservoir low level. About 150 seconds later, the SD HYD page shows the valves back to in-line green, but the Green EDP indications still show cross-line amber. What is the state?

This is the documented 150-second reopen sequence: HSMU has closed the valves on the low-level trigger, waited 150 seconds with Blue and Yellow normal, and reopened the valves to allow fluid contact with the EDPs for lubrication. The EDPs themselves have been depressurised (commanded off by the HSMU) — that is why they show cross-line amber. The valves are open, the fluid touches the pump internals (preventing dry-running damage), but the pumps are not pressurising the system. The Green system is not recoverable through this path — recovery requires the RAT path. The reopen is for pump preservation, not for system pressure restoration.

[!note]- Q5. Reading the SD HYD page is conventionally done "top down". Why top-down rather than bottom-up?

Top-down matches the architectural flow of fluid through the system: reservoir at the top (storage), through the pumps (pressurisation), through the distribution (fire shut-off valves, system manifold), out to the consumers (pressure indication at the bottom). Reading in this direction lets the crew trace cause-and-effect chains naturally — for example, a reservoir low level at the top can produce fire shut-off valve closures in the middle and pump shutdown reflected in the bottom. Reading bottom-up would mean starting at the symptom (pressure low) and working backward to the cause, which is less efficient for diagnosis. The architecture supports top-down reading by design.

References

Per FCOM DSC-29-20 (ECAM HYD Page — quantity, LO AIR PRESS, OVHT, fire shut-off valve symbols, ENG PUMP and ELEC PUMP indications, leak measurement valve indication, system pressure, colour conventions for normal/amber/white/green); FCOM DSC-29-10-20 (HSMU temperature correction logic, fail-safe default of 150 °C on sensor loss); AMM 29-31 (sensor specifications and conversion logic supporting the indication colour assignments).

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