View Full Version : A320 Y hydraulic pumps

2nd Mar 2010, 16:05
(Not so?) simple question.

If you loose the engine driven Y hydraulic pump, can the electric pump be considered as an equal alternative? Is the output the same, will it be enough to take over all the work of the engine driven pump?

Dream Land
2nd Mar 2010, 17:41
I would guess so, the Y electric pump is the same pump as the B electric pump.

2nd Mar 2010, 18:57
I would guess so, the Y electric pump is the same pump as the B electric pump. Not sure about that.

I know the A320/A330/A340 reasonably well but cannot find any information for the following:

The A320 QRH for Dual Engine Failure (Fuel Remaining, or No Fuel Remaining) indicates that while Config 3 is "selected" for the landing or the ditching, only the Slats will extend.

The Blue system powers the slats only and the Yellow pump powers the flaps. The Green system powers both.

With dual engine failure, is the assumption then, that there is no Green pressure, that the Blue Electric Pump functions but that the Yellow Pump does not function? If so, why? I can find no information, no guidance and no SOPs in the FCTM, the QRH, the expanded Abnormals in Ch3, Vol 1 explaining why the flaps are not available.

One would assume even with a dual engine failure that one could turn on the Yellow Electric pump to get the Flaps but this is not suggested/required in the QRH Dual Engine Failure drills. I can find statements indicating that the pump is used only on the ground but that does not mean it cannot be turned on in the air. There is nothing I can find anywhere in the FCOM/AOM to indicate that the Yellow Pump cannot be turned on in the air.

What am I missing?


2nd Mar 2010, 19:11
What about the overide switch above the FO's seat that the engineers use on the ground? Much faster than just using the yellow electric, or have I forgotten something again?

Dream Land
2nd Mar 2010, 19:17
I think we are speaking about the Yellow Electric Pump, what you are referring to is the Blue OVRD. Can we use the Yellow electric pump while airborne?

2nd Mar 2010, 19:33
From an AOM:

YELLOW ELEC PUMP pb sw (springloaded)
ON : The electric pump is ON.

If the electrical power supply is removed, the pump will remain off when
electrical power is applied again.

Off : The pump is off.

It comes on automatically when a crewman sets the lever of the cargo door
manual selector valve to OPEN or CLOSE.

This inhibits the operation of other yellow system functions (except alternate
braking and engine 2 reverse).

AUTO : If AC power is available, the electric pump operates :

– In flight
– On the ground, if one engine is running or if the crew has pressed the

BLUE PUMP OVRD pushbutton on the maintenance panel.
OFF : The pump is de-energized.
The words "in flight" appear beside the Blue Elec Pump, but not beside the Yellow Elec Pump.

It's still unclear however, whether one could turn on the Yellow pump in an emergency. I know there is a pump termperature issue and that an A330 burned at Toulouse as a result of a yellow pump being left on overnight (or something like that) and I see noting in Limitations ATA29 - Hydraulics on not operating the Yellow Pump.

2nd Mar 2010, 19:36
With a dual engine failure is it assumed that there is limited AC electrics available?
RAT? PTU? etc.

If you lose the Y EDP the PTU will takeover assuming the G system is nominal.

I had a logic diagram somewhere form the VACB CDRom that explained it all very well.

2nd Mar 2010, 19:47
With a dual engine failure is it assumed that there is limited AC electrics available?
RAT? PTU? etc.
Perhaps. I suspect that the minimum 150kts speed recommended is to stay above the 140kt minimum speed for RAT operation (after loss of AC1 and AC2. The RAT does power the blue system which then provides some electrical power through the Emergency Generator.

Also, a windmilling engine may be able to develop some hydraulic and electrical power at higher windmillling speeds, but again there is nothing definitive that I can find on just what is available, even anectdotally and not by test or certification.

Perhaps the answer lies in the fact that only the blue hydraulic system is powered, (by the RAT under a dual engine failure) and that is all that can be said, but the actual airplane may be able to provide more than this minimum. Still, nothing about the yellow pump...

2nd Mar 2010, 21:08
Indeed dreamland, the Y elec pump is the same as the B pump. That might be part of the answer.

But anyway, I just found the closest thing to an answer in FCOM 3.2.29 (pump low pressure)
Note : If yellow system is affected, the yellow elec pump may be used

2nd Mar 2010, 21:30
the main difference between the EDP and electric pumps is the pump output. dont quote me but the edp can output 40gallons per minute at 3000psi, the electric pump only 5.
on ground engineers use a hyd ground cart to simulate edp output.
for dual engine failure you still would have apu available assuming you still have fuel.
yellow and blue electric pumps are same part number.

2nd Mar 2010, 22:12
PENKO, Wirelock, thank you. I think putting 2+2 together, we may have good clues to an answer. First, two quotes:But anyway, I just found the closest thing to an answer in FCOM 3.2.29 (pump low pressure)

Note : If yellow system is affected, the yellow elec pump may be used , and, for dual engine failure you still would have apu available assuming you still have fuel.
We wouldn't want to start the APU in a dual engine failure because it would use up battery power, (I believe there is a caution regarding this in the QRH dual engine failure checklist). Using PENKO's quote, the pump can be used (ECAM drill for HYD G+Y SYS LO PR requires Yellow electrical pump ON if ENG 2 PUMP LO PR) but Wirelock's quote is a clue to why the Yellow pump isn't turned on. In a dual engine failure, the Blue system is hydraulically powered by the RAT but the yellow pump is electric (AC2) and the Emergency Generator (blue hyd sys) only powers the AC and DC ESS Busses.

In the QRH drill for dual engine failure, when on approach the flap lever is selected to "3" but the note indicates that only the slats will extend and they will be very slow. I think the lever is placed in the '3' posiiton to satisfy a number of computer inputs which use the flap lever position for PFD indications, GPWS, etc, but this is an educated guess only. If anyone knows the exact reason, (again, the book doesn't tell us), please let us know!

2nd Mar 2010, 23:04
Hi Penko,

FCOM 3.2.29 HYD G (Y) ENG 1 (2) Pump Lo Pr has a note:

PTU INOPERATIVE - Note : If the yellow system is affected, the yellow elec pump may be used.

I've seen an ECAM prompt to use the Y electric pump with PTU switched off and Lo Pressure Y Hyds.

2nd Mar 2010, 23:10
hi, as far as I know the Y electric pump is used in case of engine pump failure and ptu is used to provide power to Y HYD by G HYD when posible, and during dual engine failure not posible to used electric pump in order to avoid drain the batteries..:rolleyes:

3rd Mar 2010, 01:48
hi, as far as I know the Y electric pump is used in case of engine pump failure and ptu is used to provide power to Y HYD by G HYD when posible, and during dual engine failure not posible to used electric pump in order to avoid drain the batteries..

ALK A343
3rd Mar 2010, 03:15
Actually gentlemen on the newer msn A320s you can start the APU below FL250 after both engines fail. The relevant QRH checklist (ENG DUAL FAILURE - fuel remaining) has been modified. This is possible since there will be no need to fly on the batteries only after the landing gear is extended, as the rat / emergency generator powers the aircraft until touchdown.
So once the APU is online you could theoretically power the Yellow electric pump and extend the flaps. We have tried it in the simulator during the Dual engine failure exercise with forced landing.
However this is not included in the QRH checklist by Airbus and therefor would not be recommended in real life. Maybe the pump could overheat like on the A330/340. Airbus certainly has a reason not to include it.

Best regards.

3rd Mar 2010, 08:22
We seem to be getting somewhere.

Since the Y ELEC PUMP is supplied by AC2 and DC2 (FCOM 1.29.30 p1) it is not available in DUAL ENG FAIL unless we start the APU (which seems pretty sensible, in my opinion. Besides, even in the old models the flight on bats only is just a transient situation, after a go around before pushing the button and restoring EMER GEN).

The other question remains: Is the Y ELEC PMP able to move the flaps, given that it is less powerful than the Y EDP?
I think they should at least write a note explaining why the Y EDP cannot be used, or if it can be considered.

And another question: Is there an ideal configuration in case of a ditching or a forced landing, or the more the better?

3rd Mar 2010, 11:49
For a single failure Y ENG PUMP LO PR: ECAM does not ask for YELLOW ELEC PUMP ON (at least in my FCOM), but a note in FCOM 3 says you can use it. The need for it implies a double failure - eng pump and PTU - I think I would leave it off until the approach to avoid pushing my luck...

For a dual hyd failure involving Y ENG PUMP LO PR, ECAM does ask for YELLOW ELEC PUMP ON. This would keep the a/c in Normal Law and ease the workload considerably. Whether the pump has the flow rate to cope when Flaps are travelling I don't know (depends partly on which other hyd sys has failed?) - the less flight control demand in that phase the better.

DUAL ENG FAIL with fuel remaining - with the RAT running, if the engines don't relight you won't need all that battery power, so use it to start the APU to try a starter assisted relight.

PJ2: lever in FLAP 3 gives 22deg slat position compared to 27deg at FULL so a reasonably low Vapp, typically 160 kt. at MLW - GPWS etc. may not be electrically supplied? I don't know if there is another reason such as controllability - a "normal" landing with no flap would also be CONF 3 as opposed to FULL. At some point as speed is reduced the THS is frozen with no engines running, so elevator authority may be a consideration.

MB2002: The QRH DITCHING procedure with engines running says "SLATS and FLAPS .... MAX AVAIL".

manuel ortiz
3rd Mar 2010, 13:44
Ditching procedures on the A-320 are to use F3 if with Dual Eng Failure but F Full if that is not the case.

4th Mar 2010, 08:58
I believe the yellow pump is limited by electrical load. The pumps take a ridiculous amount of power, 16.2 kVA max each. Between Y and B, you've eaten up 40% of your last engine's electrical power. In the worst case, you're trying to do a APU engine start with a dual fail on a hot day at FL 200, you only get 41 kVA, plus 5 from the emer gen.

My info says the EDPs can do around 45 GPM and the electric pump does about 8, depending on version. They're sold as Vickers.

The other thing to be aware of is that all of the pumps dump heat into the hyd fluid. The fluid even runs thru the electric motor. If you run it under low pressure, you you'll cause cavitation and heat damage to the pump. If you run it dry, you'll ruin the whole thing and possibly pull an AF.

I bet the reasoning behind the Y EDP failure checklist is that if you lose your Y EDP and the PTU can't bring pressure back, there's no need to risk breaking a third pump until things get desperate.

františek dobrota
4th Mar 2010, 19:48
Flaps are not extended during dual engine loss due to simple reason - no hydraulic power for actuation. Flap PCU is powered by green/yellow hyd. system, but in this situation is only blue system pressurized by RAT. Slats speed is significantly limited due to RAT pump limited flow/pressure output. Slats are preferred for increased AOT and aerodynamics reason.Both electric Y and B not powered .Otherwise yellow elec. pup is strong enough to operate flaps, but in longer time compared with EDP time, as you can see during ground flaps/slats extension for maintenance purposes with no engines running.
Regards F.

4th Mar 2010, 20:53
The Yellow electric pump is in the Yellow hydraulic compartment. It supplies the Yellow main system with hydraulic power when necessary (failure of the engine or engine pump). It is set to on from the flight compartment. It also starts when the aircraft is on the ground and a selection is made to operate the cargo doors.

It is not meant to replace/amend your ABN/EMER PROC but if you really need that pump, you can use it!

Y ELEC Pump Performance:
- displacement = 4.3 ml/rev.
- delivery pressure at zero flow = 206 + 3 - 0 bar (2987 + 43.5 - 0 psi)
- delivery pressure at 23 l/min (6.08 US gal/min) = 196 bar (2842 psi)
- delivery pressure at 32 l/min (8.45 US gal/min) = 150 bar (2175 psi)

20th Nov 2010, 16:20
In a dual engine failure situation assuming you got your APU started and running, what is the state of the electrical configuration? Since the APU is an identical generator to either engine's, will there be a full recovery of the electrical systems?

Edit: Oops I do apologise posting this reply on the wrong thread. I was doing a search and ended up having a few threads open simultaneously and I only just realised I posted an electrical question in a hydraulics thread.

21st Nov 2010, 06:55
Have a look at FCOM 3.02.29 HYD Y ELC PUMP LO PR or OVHT

It is suggesting that it can be used in the event of a PTU and Y ENG PUMP failure. I haven't seen though where the procedure is written to turn it on in the first place. Vol 1 implies that it can only be used on the ground but that is a bit of red herring. I look forward to the definitive answer.

21st Nov 2010, 13:56
Dream 747, actually your question is relevant here:

It is not the same to have two engines inoperative and no APU than two engines inoperative with the APU running. The latter is much less stressing for the crew, to say the least.

So, with APU running, the question remains: Y ELEC PUMP, yes or no?

If the Airbus engineers don't use it in the procedure, it is because something could be not OK with that. There's a few things to consider: The output power of the Y ELEC is very limited, it seems.

If I was to use it, I would turn the PTU OFF first, so the elec pump wouldn't also have to power the green system. Then I would turn the Y ELEC ON and use it: Conf 3, then turn it off again.

As an added thought, APU ON take offs could could become standard procedure when there are birds in the airfield.

21st Nov 2010, 19:37
For readers who may have been lost in detail...
in general terms...
Electric pumps almost always have less flow than eng driven devices.They are capable of full pressure but flow rates are much less therefore for hi flow devices pressure will drop markedly.

Engines, even if not operating in flt will in most cases have sufficient power to generate hyd pressure if still selected on , pump is OK and fluid level sufficient.Witness how quickly hyd pressure comes up during starter ops prior to light off.

22nd Nov 2010, 07:22
So, with windmilling engines, Would be have enough power to set landing configuration?

In any case, at least on the ground without any aerodynamic loads, the yellow elec can lower the flaps. I wonder if that would not be the case when in the air at, say 200 Kt.

22nd Nov 2010, 23:01
It will it is just slower with the lower flow rate.The pump will produce full pressure but will sag with load but it will deploy whatever it is pushing.
I am reasonably confident a windmilling engine would produce enough to run hyd's with flow limits.There are obviously some issues with having elec power to allow commands to made of the surfaces / device.
Consult the MM and NNC for further info

23rd Nov 2010, 15:30
The Yellow and Blue pumps are interchangeable.

The blue elec pump u/s is non-dispatchable so it is quite common to swap the serviceable Yellow for the Blue, non main base, to dispatch the aircraft.

Dual Engine failure high up would be within the windmilling re-light envelope therefore EDPs still available, if you dropped out of the envelope would you not attempt an APU start for more puff anyway thus giving you the electric power for ACMP? Being in engineering have no idea on the QRH/FCOM procedure.

As for the flow/delivery rate of the electric pumps, I regularly retract the Aircraft undercarriage (on jacks) using the yellow pump through the PTU, bit slow and whines a bit but it gets up there!

25th Nov 2010, 07:06
Thanks for that

You Engineers should share with us more stuff like that


320 driver
8th Dec 2010, 23:51
Worth noting that the EDPs will provide some useful pressure right down to approach speed so you are using the yellow as a top up.

Having yellow hyd gives a lot of advantages, configuration is one but braking/steering is also useful (newer A/C use yellow for nose wheel steering).

On the elec configuration subject. After a dual eng fail or Emergency Elec Config, even if you recover 1 or 2 main generators the essential buses remain supplied by the emergency generator until reset on the ground although other services are recovered through main buses.