Typical Day Operations

This article walks through the hydraulic system from the crew's perspective across a complete flight — from pre-departure walkaround to post-shutdown. The aim is to show what the system does during normal operation, when the crew sees specific indications, and what brief observations to make at each phase.

Almost all hydraulic activity is invisible during a normal flight. The pumps run, the surfaces respond, and the SD HYD page shows steady values. But there are specific moments where the architecture's design is visible — and a pilot familiar with the system reads each indication as a confirmation that everything is operating as expected.

1. Pre-departure walkaround and cockpit setup

Walkaround

External hydraulic inspection during the walkaround:

• Hydraulic fluid stains. Any fluid on the airframe near hydraulic lines, the wing/fuselage joint, the engine pylons, or the landing gear bays is reported. Phosphate-ester fluid (Skydrol family) is corrosive to paint and a sign of an internal leak that maintenance must trace.
• Pump access panels closed. Engine accessory gearbox access panels in the engine cowlings should be properly secured. Hand-pump handle should be present at the Green ground service panel (not at the Yellow panel where the hand pump body is).
• RAT door. The RAT bay door on the right wing's flap track fairing #4 should be flush with the wing skin. A protruding door or a deployed RAT visible from outside is significant.
• Ground service panels. Blue ground service panel (which hosts most pressurisation ground connectors) and Green ground service panel (which hosts the gas-pressure gauge and hand-pump handle) should be closed and locked.

Cockpit pre-departure

With electrical power but no engines running:

• SD HYD page. Reservoir quantities in green band on all three systems. No OVHT, no LO AIR PRESS annunciations. Reservoir cushion still pressurised from the previous flight or ground source (12-hour static seal).
• Overhead 29 panel. Pushbuttons in their normal positions. No FAULT lights illuminated.
• MEMO strip. No HYD ELEC PUMP, no RAT OUT.

APU-running phase

With APU running, APU bleed becomes available. Crossbleed picks up if Engine 1 is not running — reservoir pressurisation continues normally. The pilot does not see specific hydraulic activity; the architecture has just confirmed the bleed-source backup chain.

2. Engine start

Engine 1 start

• The Green EDP on Engine 1 begins to rotate as Engine 1 spools up.
• The Blue EDP on Engine 1 begins to rotate.
• The pressure in Green and Blue reservoirs is being maintained from before; the pumps now ramp up output.
• SD HYD page shows Green and Blue pressures rising as the engines reach idle.
• No FAULT lights, no cautions if everything is normal.

Engine 2 start

• The second Green EDP (driven by Engine 2) and the Yellow EDP begin to rotate.
• Green system now has both EDPs contributing.
• Yellow comes up to 3000 psi.
• SD HYD page shows all three systems at 3000 psi, all pumps in-line green.

The pilot's mental check at this point: all three systems are pressurised, all pump indications healthy, no FAULT lights. This is the normal "ready for taxi" hydraulic state.

3. Taxi

During taxi:

• Nose wheel steering uses Green hydraulic pressure (with Yellow as alternate).
• Normal braking uses Green (with Yellow alternate available).
• Spoilers do not deploy.
• Slats/flaps may be moved into takeoff configuration (using both Green and Yellow flap motors).

Visible to the pilot:

• Brief Green pressure dips as nose wheel steering inputs occur — quickly recovered by the EDPs.
• Brief Yellow pressure dips as flap motors run.
• No FAULT lights, no cautions in normal operation.

The hydraulic system is doing real work during taxi but the architecture absorbs the dynamic loads — accumulators smooth pressure, EDPs maintain steady-state, and the SD HYD page shows steady values.

4. Takeoff and initial climb

Pre-takeoff

• Slats and flaps fully extended to takeoff configuration.
• Spoilers armed (will deploy automatically on landing).
• All three systems at 3000 psi.
• RAT OUT not present.

Takeoff roll

• Limited hydraulic activity during the ground roll.
• Nose wheel steering active until 80 kt or so (depending on operational SOP).
• Spoilers may deploy if a rejected takeoff occurs.

Initial climb — gear retraction

This is the first significant hydraulic event of the flight:

• Crew selects gear lever UP.
• Green hydraulic pressure releases the gear downlocks.
• Green pressure drives the gear actuators up.
• Pressure dip on the SD HYD page Green column — brief, normally clears in seconds.
• Gear reaches the UP and LOCKED position.
• If the Green ELEC PUMP automatic trigger condition is met (engine failure during gear-up cycle), it would run for 25 seconds — but in a normal takeoff, the trigger does not fire.

Flap retraction

• Crew schedules flap retraction per the after-takeoff profile.
• Each flap-detent change uses both Green and Yellow flap motors.
• SD HYD page shows brief pressure dips on both Green and Yellow during transitions.
• Normal operation completes the retraction without FAULT illuminations.

After flap retraction is complete, the aircraft is in clean configuration. The hydraulic system is supplying mostly to flight controls and continuous functions. Steady-state pressures on all three systems.

5. Cruise

Cruise is the quietest phase for the hydraulic system. With no configuration changes and flight controls in steady-state, demand on each system is minimal. The variable-displacement pumps automatically reduce their stroke to near-zero, conserving engine power.

Pilot observations during cruise:

• SD HYD page shows steady 3000 psi on all three systems.
• All pump indications in-line green.
• No FAULT lights, no MEMOs.
• No automatic electric pump triggers (none should fire in steady cruise).
• Reservoir quantities stable in green band.

The architecture is doing its job invisibly. The crew can monitor the SD HYD page periodically as part of normal flight monitoring, but no action is required.

6. Descent

Descent introduces some hydraulic activity:

• Speed brake (spoiler) deployment for descent rate management. Each deployment draws flow from Green; the accumulator smooths the pressure transient.
• Reverse-direction speed brakes (the spoiler-up extension) are routine in many operations.

Pilot observations:

• Brief Green pressure dips during speed brake activity, quickly recovered.
• Yellow pressure remains steady (no Yellow consumers during this phase except potentially flap pre-positioning later).
• No FAULT lights.

7. Approach

Approach configuration changes:

• Slats and flaps extended through the approach detents.
• Each detent change uses both Green and Yellow flap motors.
• Gear extension at the appropriate point.

Gear extension

• Crew selects gear lever DOWN.
• Green hydraulic pressure releases the gear uplocks.
• Green pressure drives the gear actuators down.
• Brief Green pressure dip on the SD HYD page.
• Gear reaches DOWN and LOCKED.

Spoiler arming and final approach

• Spoilers armed for automatic deployment on touchdown.
• Final flap detent set.
• All systems at 3000 psi steady-state.

The hydraulic system has now completed its descent-and-approach configuration changes. From this point until touchdown, the activity is mostly flight-control surface motion responding to autopilot or hand-flying inputs.

8. Landing

Touchdown

• Main gear wheels contact runway.
• Weight-on-wheels switches trigger.
• Spoilers deploy automatically (Green and Yellow flow).
• Reverse thrust selected — Engine 1 reverser uses Blue hydraulic, Engine 2 reverser uses Yellow hydraulic.
• Wheel brakes applied — normal brakes use Green.

Rollout

• Brief Green pressure dips during heavy brake demand and reverser deployment.
• Spoilers deploy fully; flight spoilers retract during the rollout.
• Anti-skid system modulates braking.

Pilot observations:

• SD HYD page shows brief Green pressure dips, quickly recovered.
• All systems remain pressurised.
• No FAULT lights in normal operation.

After-landing taxi

• Flaps retracted to taxi configuration.
• Reverser stowed.
• Normal braking continues.

9. Post-shutdown

Engine shutdown

• Engine 1 stops. Both Green EDPs continue to rotate briefly with the engine, then stop. Blue EDP stops.
• Engine 2 stops. Yellow EDP stops. Green's second EDP stops.
• All four EDPs are now stopped.
• The accumulators maintain pressure briefly; the system pressure decays gradually.
• SD HYD page shows the pressure decay; no FAULT lights because the engines are stopped (pump-low-pressure trigger is inhibited on ground with engines stopped).

APU running, ground power

• If APU is running, reservoir pressurisation continues from APU bleed via the crossbleed duct.
• Reservoir cushions remain at 4.5 bar absolute.
• The 12-hour static seal will preserve cushion pressure for the next 12 hours, with or without APU running.

Parking brake

• Crew sets the parking brake.
• The Blue brake accumulator (preserved from the landing's pressure) maintains the parking brake for the duration of the parked period.
• Over time, the accumulator's pressure depletes slowly. For long parked periods, the parking brake may not hold pressure indefinitely; chocks are placed by ground personnel as a precaution.

Cargo loading

• If electrical power is available, the Yellow electric pump runs during cargo-door operation.
• If no electrical power is available (cold-and-dark aircraft), ground personnel use the Yellow hand pump.

10. The day's hydraulic events — summary

In a normal turnaround flight, the hydraulic system performs these activities:

Each activity is brief and invisible from the cockpit beyond the SD HYD page indications. The architecture absorbs the dynamic loads, maintains 3000 psi, and protects against any unexpected condition (FAULT lights, ECAM cautions if needed). The pilot's role across the day is monitoring, not intervention.

11. The four standard scan moments

Across the day, the SD HYD page is checked formally at four moments. These are the points where any developing anomaly should be detected:

Outside these moments, hydraulic monitoring is essentially passive — the architecture provides automatic warnings, and the crew has no need for continuous scrutiny. The four-moment discipline ensures that changes (vs the baseline) are detected: a drift in quantity, a developing fault, a recurring transient.

12. Inhibit windows — when ECAM cautions are suppressed

The ECAM warning system inhibits certain cautions during specific flight phases to avoid distracting the crew during high-workload moments. This includes some hydraulic-related cautions:

For hydraulic events specifically:

• A LO PR or LO AIR PRESS condition triggered during takeoff roll is not suppressed if it represents an immediate flight-safety concern — but a RSVR OVHT caution might be delayed by the inhibit logic until after the critical phase.
• A reservoir-quantity alert is typically informational and may be delayed.
• A real SYS LO PR is treated as critical and is shown promptly.

The pilot's takeaway: during the inhibit windows, the absence of a caution does not necessarily mean the system is healthy. After clearing the critical phase, a brief re-scan of the SD HYD page verifies state. The architecture is designed so that critical anomalies still get through; only delayed-priority cautions are temporarily suppressed.

The complete inhibit-window logic spans the warning system architecture (FCOM and FCTM) and is detailed in Hydraulic Warnings Reference.

13. The three electric pumps — automatic activation opportunities across the day

Across a normal flight day, the three electric pumps have specific moments when their automatic triggers may activate:

Green ELEC PUMP

• Activation moment: One-engine failure in flight, with gear lever selected UP → runs for 25 seconds (per FCOM DSC-29-10-20).
• Most likely occurrence: During or shortly after initial climb if an engine fails during gear-up.
• Normal day: Should never activate.

Blue ELEC PUMP

• Activation moment: Engine 1 failure combined with PRIM 1 or PRIM 3 fault, in flight.
• Most likely occurrence: An unusual combined fault scenario, not phase-specific.
• Normal day: Should never activate.

Yellow ELEC PUMP

• In-flight activation: Engine 2 failure with FLAPS lever ≠ 0 → runs until condition clears (per FCOM DSC-29-10-20).
• Ground activation: Cargo door operation (electric pump runs during door cycle, leak measurement valve closes automatically).
• Most likely occurrence: The ground cargo-door operation is routine; the in-flight activation is abnormal.
• Normal day: One or more activations during ground servicing of cargo doors.

The crew sees the HYD ELEC PUMP MEMO when any electric pump runs. On a normal day, this memo would appear only during ground cargo-door operations and not in flight. An in-flight HYD ELEC PUMP MEMO that the crew did not select manually indicates that one of the automatic triggers has activated — investigation via the SD HYD page identifies which pump and which underlying condition.

14. End-of-day maintenance interface

After a normal flight day, the maintenance interface for hydraulics is light:

The "normal day" hydraulic activity is routine — no abnormal events, no FAULT lights, no fluid issues. Maintenance attention is on scheduled inspection rather than reactive troubleshooting. The architecture is designed so that this is the typical day; abnormal events are rare and well-documented when they occur.

Self-test

[!note]- Q1. During taxi, the SD HYD page Green pressure dips briefly each time the nose wheel steering tiller is moved sharply. The pressure recovers within a second or two. Is this normal?

Yes, normal. Nose wheel steering is a Green-supplied function that can demand significant flow during sharp inputs. The brief pressure dip is the system responding to the demand; the EDPs ramp up output and the accumulator absorbs the transient. The pressure recovery is the architecture working as designed. Persistent low pressure or non-recovery would indicate a problem; brief dips during demand are routine.

[!note]- Q2. The aircraft was cold and dark overnight (16 hours of inactivity). The crew arrives and finds HYD G RSVR LO AIR PRESS and HYD B RSVR LO AIR PRESS annunciated. Is this a system fault?

Not a system fault — it is the expected condition after 16 hours of cold-and-dark (beyond the 12-hour static seal design). The reservoir cushions have decayed below the 1.5 bar relative threshold. The standard maintenance action is to use a ground source (via the blue ground service panel connectors) to repressurise the reservoirs before engine start. Once pressurised, the cautions clear. The HSMU is correctly reporting an expected condition; the architecture's recovery is ground-source supply.

[!note]- Q3. During gear retraction after takeoff, the crew expects to see Green ELEC PUMP MEMO if the automatic trigger fires. In a normal takeoff with both engines healthy, the MEMO does not appear. Is the trigger broken?

No. The Green ELEC PUMP automatic trigger requires an engine failure as one of the conditions (per FCOM DSC-29-10-20: one-engine failure + gear lever UP in flight = pump runs for 25 seconds). In a normal takeoff with both engines operating, the engine-failure condition is not met, so the trigger does not fire. The MEMO would only appear if an engine actually failed during the gear-up phase. The trigger working correctly does not produce an indication in normal operation.

[!note]- Q4. After a normal landing, the parking brake is set. Several hours later, ground personnel report the parking brake is no longer holding pressure. Did the brake fail?

Not failure — depletion. The parking brake holds pressure from the Blue brake accumulator. With no Blue pump running (engines off, electric pump off), the accumulator gradually loses pressure through small system losses over time. After several hours, the accumulator pressure has decayed below the level required to hold the brake. The standard practice is to place chocks under the wheels promptly after shutdown for any extended parked period, recognising that the parking brake is a short-duration restraint, not a multi-hour one.

[!note]- Q5. During cruise, the SD HYD page shows all three systems at 3000 psi with all pumps in-line green. The crew is briefed for a long flight (10 hours overwater). What hydraulic-specific items should the crew monitor during cruise?

Periodic monitoring of the SD HYD page is the primary discipline. The crew watches for:

• Reservoir quantity trends (any gradual decrease suggests a slow leak).
• Reservoir OVHT (sustained high pump demand or cooling issue).
• Reservoir LO AIR PRESS (bleed source issues).
• Any FAULT light illumination on the overhead 29 panel.
• Pressure stability (sudden dips on any system warrant investigation).

In normal cruise, the system is uneventful, and monitoring is brief — perhaps once per hour as part of normal flight monitoring. The architecture's reliability is high enough that intensive monitoring is not required, but the awareness of what would indicate a problem helps the crew catch any developing condition early.

References

Per FCOM DSC-29 (Hydraulic System Description) and FCOM PRO-NOR (Normal Procedures for hydraulic-related actions); FCOM DSC-29-20 (cockpit indications during normal operation); operational SOPs of typical operators for normal procedure flow.

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