A320 Dual Hydraulic Failure

[Boyington]

In an A320 in case of Dual Hydraulic failure and if failure of one pump is caused due to Overheat when is it recommended to recover the system? The obvious answer is when the OVHT condition has disappeared. But should one do it immediately or do it at a later stage?
For example in G+B with Green OVHT should one restore the system before switching OFF the A/THR as given in the sequence in the FCOM or can one wait longer?

[vilas]

It is part of the approach procedure to put the pump on if overheat is out. You should carry out all actions for dual hydraulic failure (landing distance etc) just in case you don't get the G back.Then before the approach begins put the G pump on. If sufficient time has elapsed after switching off it should hold till you land.

[Bkdoss]

Pardon me for ever so slightly digressing from the topic, in case of Yellow Engine Driven Pump fault with the Green or Blue system already lost, would it be OK to use the Yellow Electric Pumps to pressurize the yellow system and get out of dual hydraulic condition though the ECAM procedure doesn't suggest turning it ON?

[vilas]

Bkdoss
would it be OK to use the Yellow Electric Pumps to pressurize the yellow system and get out of dual hydraulic condition though the ECAM procedure doesn't suggest turning it ON? When even with single yellow EDP fail and PTU inop ECAM suggests you to switch on the yellow electric pump, why would the ECAM with dual hydraulic fail not suggest it? did you check? The ECAM procedure is very logical. First thing, PTU or any pump can be on only if there is fluid, no overheat or reservoir low pressure. Between G and Y since the PTU does the job Y electric is not required. But if PTU is inop it will ask for Y electric pump. Then comes dual hydraulic. It will suggest to convert it to single hydraulic by switching on Y electric for G+Y (with PTU OFF as it cannot sustain both) and for G+B in case B elec pump fail will ask for RAT manual lowering. Only single B elec pump fail it will not ask for RAT manual as it cannot be retracted.

[Metro man]

The Yellow electric pump is unable to retract the landing gear if it's the sole source of pressure.

[vilas]

Metro man
Are you talking about airbus? What has yellow system got to do with landing gear?

[Metro man]

Green plus Yellow engine pumps fail, Yellow electric pump can pressurise both systems through the PTU but can't provide enough pressure to retract the gear.

[vilas]

FROM Y electric pump You cannot pressurize green through PTU. Yellow electric pump delivers only 32L/mt that is 1/4 th of yellow EDP. That will cause yellow also to fail. ECAM will ask you to switch off PTU.

[dream747]

Is that why also, in a dual engine failure situation, no where in any procedures tells us we can use the Y elec pump?

Tried it in the Sim by turning the yellow elect pump it works fine enough to provide both green and yellow pressure through the PTU though.

[vilas]

dream747

Actually dual engine flame out does tell you to put the yellow electric pump on only when the wind milling is not sufficient to generate enough yellow pressure. In SIM it may have worked because of the wind milling assistance otherwise it would fail both systems

[Metro man]

I heard of a sim check for a Chinese airline which involved G + B HYD failure, then No. 2 engine fire. Little other option left but to put the Y elec. pump on.

[dream747]

Hi Vilas, where is this written? It's not in the Dual Eng procedure, at least not in the latest revision that I have.

[vilas]

I obtained the answer from airbus. As I said in post 4 it is very logical.

[PENKO]

Ah yes, logical, but it's not written down anywhere to switch on the Y electric pump in a dual engine failure. As with everything Airbus: if it is not written down, it is highly dubious!

(you know how it goes..)

[Goldenrivett]

If the APU electric generator is recovered and G + Y SYS pressures are low (<1450 psi), then ECAM displays the conditional line to turn the Y Elec pump on.
PTU remains off to ensure the flight controls receive sufficient HYD pressure.

[vilas]

PENKO and Golden
It is in ECAM but you don't get to see it because normally in the simulator wind milling generates enough hydraulic pressure. When the wind milling does not generate sufficient pressure it will ask you to put the yellow electric pump on. Flight controls are working on blue and continue to do so but the yellow pump will fail with extra load because it supplies only 32 l/mt as against 140 I/mt by EDP.

[Metro man]

For info, if you have a BLUE HYD pump fail, engineers can swap it with the YELLOW ELEC pump if needed to get you home. Job takes around four hours and the cargo doors need hand pumping but it beats an AOG.

[PENKO]

Vilas, thanks for that. Did Airbus clarify why they did not incorporate switching on the Y electric pump in the paper ENG DUAL FAILURE QRH checklist? That checklists specifically states you will only have slats and insists on speeds greater that 150 knots for the rat. One could do better with the Y-electric pump and APU running the Blue...

The more I look into that QRH, the more questions arise!

[Goldenrivett]

Hi PENKO,
One could do better with the Y-electric pump and APU running the Blue...
I agree. It would only take a couple of extra lines in the QRH.

If neither engine relights but APU geny is on line, the windmilling driven hydraulic pumps only cause ECAM to display that nugget of information when speed is below GD and when your work load is highest. It is often missed by crews because ECAM becomes a distraction reminding them of STATUS again etc.

[vilas]

PENKO
I also feel that dual engine flame out needs to be more straight forward and once ECAM switches the pilot to paper procedure it should be self contained and should obviate any need to refer ECAM again.
The ECAM portion which is under ENG DUAL FAILURE states the following status:
APPR PROC
IF HYD NOT RECOVERED:


FOR LDG............................................... USE FLAP 3


But it doesn't say how to recover hydraulics. The line
IF HYD NOT RECOVERED should be preceded by Yellow Electric pump ON.

[CMpilot1]

Vilas,

Did you mean that this is applicable only in the air? According to my understanding PTU allows the green system to be pressurized on the ground when the engines are stopped. This can be done by switching on the Y electric pump.

[Earl Eagrave]

A reply I received previously from Airbus:

If fuel remains, if the yellow hydraulic system is in good condition, if the APU, the APU generator and the YEP are operative and usable at the time of the all engines failure event, then, the PTU must be switched off in order to isolate the green and the yellow systems. The YEP alone cannot pressurize both systems: The yellow electric pump characteristics (pressure/delivery curves) and the PTU efficiency are such that the YEP may just supply the Yellow and Green systems leaks if the PTU remains on.

However, even if the PTU is switched off, the extension of flaps is theoretically possible, but the deployment will be slow and probably periodically stopped due to interaction with the priority valve, depending on the hydraulic demand of the other consumers. The priority valve will shut off the supply to the flap motor in the case of low system pressure to protect the primary flight controls: As a result, the flaps may extend to an unknown position. The effects of such fluctuations of the yellow hydraulic pressure on the aircraft operation depend on many parameters and are not predictable.

If the Pilot Monitoring (PM) is distracted, and doesn’t manage to obtain the proper hydraulic system configuration, the aircraft might end up flying in a configuration with unknown results (i.e. YEP supplying both yellow and green hydraulic systems).

All engines failure event is a very demanding situation. During this short period of time, the crew's major concern is to attempt engines relight and/or to find a suitable landing field. Despite the potential benefits that could be envisaged from the use of the YEP in some very specific conditions, it is not worth complicating the procedure for the majority of cases and most probable scenarios.

For all the above reasons, Airbus did not opt for the use of the YEP in the procedures addressing the all engines failure situations (EMERGENCY LANDING procedure and ENG DUAL FAILURE procedure).

[FlightDetent]

E. E. thank you so much.

[giord]

Hello,

in case of G+Y HYD both reversers are inop. As per FCTM when both reversers are inop no reverse thrust should be selected. Is it correct?

Thanks.

[Goldenrivett]

Hello,

in case of G+Y HYD both reversers are inop. As per FCTM when both reversers are inop no reverse thrust should be selected. Is it correct?

Thanks.
Correct. Since the reverse “buckets” won’t deploy, selecting reverse thrust simply accelerates the engines to “Rev idle or more RPM” which would then produce more fwd thrust.

[giord]

Correct. Since the reverse “buckets” won’t deploy, selecting reverse thrust simply accelerates the engines to “Rev idle or more RPM” which would then produce more fwd thrust.

Thank You very much!:)