Airbus Dual Eng Fail procedure question

[clonecity1]

QRH 70.01 Dual Eng Failure:
Why the reset of FAC1?

Happy Landings boys,
CC1

[vilas]

When AC busses fail FACs fail. On EMER GEN only FAC1 is available after reset. Why do we need it? Because right aileron is not hydraulicly supplied so it floats causing roll which can be trimmed off by rudder trim

[rudderrudderrat]

Hi vilas,

Because right aileron is not hydraulicly supplied so it floats causing roll....
On A320 series, both ailerons are powered by the Blue system. What aircraft are you referring to?

[vilas]

Rudderrudderrat
I am referring to A320. Check PRO-ABN-70P31/54 below FAC1---OFF THEN ON

[rudderrudderrat]

vilas

Why do we need it? Because right aileron is not hydraulicly supplied so it
floats causing roll which can be trimmed off by rudder trim....
A320

Both L & R ailerons are powered by G & B
With the RAT deployed, Blue Hyds available.
Please explain why you think the right aileron would "float".
Thank you for explaining how to reset a FAC.

[vilas]

rudderrudderrat
It is not my thinking I have given you a reference which is in black and white. Kindly refer to that. Blue and green supply ailerons normally but in dual flame out green is lost and blue when driven by rat only produces 2500 psi. That could possibly be the reason. mind you only right aileron is shed.

[rudderrudderrat]

vilas,
mind you only right aileron is shed.
Post #12 from G & Y Hyds Failure. I teach every other day.
I certainly hope you are not teaching that sort of misinformation.
Where does it say so?

[vilas]

About aileron shedding I have quoted Airbus manual. I do it again for you. PRO-ABN-70 P31/54 You check and get back. And about G+Y what I quoted is 100 percent correct. you can check that also and offer your views.

[clonecity1]

Good knowledge,Cheers gents.
Aileron possibly to do with Elac2 u/s?just a suggestion.
CC1

[rudderrudderrat]

vilas,
Thanks for the reference, and you are correct - it does say when the hydraulic power is lost, the RH aileron will float - but I have no idea why that is so.

[KBPsen]

ELAC 1 controls the blue actuator on the LH aileron and the green actuator on the RH aileron. This means that if no green hydraulic pressure is available, the RH aileron is inoperative as the blue actuator is in damping mode. Some floating may occur.

It has nothing to do with RAT pressure or an aileron being 'shed'. It is simply a result of system architecture.

The ability to quote manuals does not necessarily indicate system understanding, it seems.

[GlidingAerobats]

Hi guys!

One thing, I do not quite understand about the whole issue is why ELAC 2 is unservicable in Elec Emer Config?

Checking the bus equipment list, gives DC ESS for ELAC1 and DC2 for ELAC2 in normal circumstances. I can understand that if this was the only supply, ELAC 2 would be U/S with a Dual Eng Fail, as DC2 is gone.

However, the bus equipment list also gives HOT1 for ELAC1 and HOT2 for ELAC2 as "standby supply". The HOT busses are directly connected to the batteries, so they are always powered until your batteries are flat.

Shouldn't the ELAC2 continue living of the HOT2 bus for the remainder of the flight (and control the RH aileron via the blue Hyd), even with the aircraft in Elec Emer Config? What am I missing here?

Thanks for your help,

Torsten

[KBPsen]

ELAC 2 is powered by battery 2 if normal power fails, but only for 30 seconds after which it is de-energized. This is presumably to cover a temporary loss of normal electrical power and to save batt 2 in case the loss is not temporary.

ELAC 2 is connected again to batt 2 when the nose gear is extended.

[GlidingAerobats]

Awesome. Thanks for the additional info.

The reenergizing with the gear extended is to improve handling qualities in the approach?

Torsten

[vilas]

KBPSen
Thanks for your input. Let noble thoughts come from every where ( even with brickbats). May be you can answer my query about G+Y fail. You can see my post on this.

[Yurich]

Why ENG DUAL PROC does not require to switch on Y ELEC PUMP when APU is avail? We lost G and Y HYD SYS so can we recover HYD SYS by using Y ELEC PUMP? I asked you due to FCOM ABN HYD G+Y SYS LO PR asked:
 If yellow sys lost by ENG 2 PUMP LO PR:
YELLOW ELEC PUMP..................ON
And what does it mean "IF HYD NOT RECOVERED" in PRO-ABN-70:

STATUS page
.............
APPR PROC
 IF HYD NOT RECOVERED:
FOR LDG............................................... USE FLAP 3
?
So, can HYD SYS be recovered by Y ELEC PUMP or by airflow when windmill is good?
Thank you!

[rudderrudderrat]

Hi Yurich,
In our simulators, with airspeed >about 220Kts, then the wind milling engines can keep the Hyd pressure OK.
If the APU generator is on line and Y Hyd pressure is low, ECAM asks you to turn the Y Elec Hyd Pump on.

[Chris Scott]

In the absence of a QRH or FCOM here, I'm just wondering in what circumstances you would not want to turn on the yellow AC Pump (assuming fluid present) in the event that the APU generator was available? That Yellow-SYS pressure from the windmilling No. 2 engine ED Pump will decline as soon as you slow down for the approach.

Can you guys confirm that it is still policy to make one attempt at an APU start in the Dual-ENGINES failure case?

[rudderrudderrat]

Hi Chris,
Affirm.
If there is fuel remaining, then QRH asks to attempt APU start when below FL250.
QRH does not assume APU Generator comes on line and hence procedure is worst case scenario.

[fruitloop]

I think that the reasoning of "ONLY" 1 start attempt is to maintain the 30 minutes duration of the Batteries ...

[vilas]

Yurich
Dual Eng Fail with APU available if the windmill is insufficient for hydraulics ECAM will ask for PTU OFF and Y electric pump on. You can recover flaps to land in CONF3. Each start attempt I think reduces battery life by 3mts.

[Yurich]

vilas
You are right! In case of
HYD Y ENG 2 PUMP LO PR (PTU INOPERATIVE)

YELLOW ENG 2 PUMP........................................................ ...................OFF
ASSOCIATED PROCEDURES
Y SYS LO PR
Note: If yellow system is affected, the yellow electrical pump may be used.

So, if we lost Y HYD SYS and fluids are available we can turn on Y ELEC PUMP but PTU should be OFF (INOP).

[Chris Scott]

Seems to make a lot of sense to delay APU start attempt until below FL250. That's about 10 - 15 mins before landing, depending on terrain? So, with the Blue RAT Pump and the Yellow AC pump, you can get the slats and flaps out without depending on engines windmilling.

With no PTU, Green SYS press will depend on No 1 ED Pump windmilling. If no runway available, and landing rather than ditching, is extension of L/G recommended? Or is it simply pilot's discretion? Might need to be free-fallen...

Bon courage!

[vilas]

Chris Scot
On ELEC EMER Config APU start is limited to FL 250 and bleed below 200. It is not an option. Also landing gear is to be selected before 3000feet. It is also not an option. Gear can withstand hard impact. Landing on fuselage is likely to break it up

[Chris Scott]

Quote:
On ELEC EMER Config APU start is limited to FL 250 and bleed below 200. It is not an option. Also landing gear is to be selected before 3000feet. It is also not an option. Gear can withstand hard impact. Landing on fuselage is likely to break it up

WILCO vilas!

[vilas]

Chris
I also flew DC3 as my first aircraft.

[rudderrudderrat]

Villas
Also landing gear is to be selected before 3000feet. It is also not an option.
If I was attempting a landing with dual engine failure and I was a bit lower than ideal around 3,000 ft - I would probably delay lowering the very draggy gear until I was certain I could make the runway.

However, if you must do it by the numbers - then fill your boots.

[vilas]

RRR
No option was between gear down and belly landing. If undershootin can be fatal you lower it later but lower it. Even collapsing gear is better than belly landing.

[Natstrackalpha]

I believe you are right . . .

I am looking at why [ if that is indeed the case] the RAT cannot give enough juice in the Hyd genny to power APU start attempts

- am trying to balance this off against "a successful APU start from the batt is unlikely" . . back to the books, I guess. . .

[Chris Scott]

Quote from Natstrackalpha:
I am looking at why [ if that is indeed the case] the RAT cannot give enough juice in the Hyd genny to power APU start attempts
- am trying to balance this off against "a successful APU start from the batt is unlikely" . . back to the books, I guess. . .

No manuals or QRH to hand, but if and when you have a chance try selecting the ELEC page on ECAM during a routine APU start on AC EXT PWR. Naturally, the 28V DC has to be produced by the TRs. (I emphasise the plural because, in the early days, TR1 had to do it alone.)

You'll see that both TR1 and TR2 quickly achieve 300 amps, which is top-of-scale on the read-out. Additionally, the two BATS register considerable current draws. That situation lasts for some seconds until the generator effect kicks in as the APU starter motor (and the APU itself) accelerate.

Having said that, the BATs always achieved reliable APU starts at sea-level in my experience, even on a cold morning.

[vilas]

Nats
APU starts with battery and in ELEC EMER CONFIG they do not get charged from emergency generater So you loose 3mts of battery for each start attempt.

[Chris Scott]

I see that vilas has done a much better job of addressing Natstrackalpha's question than I did!

What I meant to go on to say was that, if you use the ECAM ELEC page to estimate the peak 28VDC load demanded by the APU starter motor during a routine sea-level start, it may be in excess of 800A (a bit like the engine starter motor of a very large family car, but at a higher voltage). I would suggest that the AC power involved to produce that would be beyond the capability of the RAT emergency generator - hence the Emergency TR is not given that task.

In any case, that noisey little RAT has the far more important task of pressurising the Blue hydraulic system, which sustains the primary flying controls in the double-engine failure case. (Any Green and/or Yellow hydraulic pressure from windmilling engines is simply an unreliable bonus.)

[aterpster]

Isn't everyone going to die anyway?

[bubbers44]

No, because some pilots can handle it, others can't.

[TyroPicard]

Natstrackalpha ...
The A320 APU ALWAYS starts from battery power, even with fully powered electrical system.

[Natstrackalpha]

The A320 APU ALWAYS starts from battery power, even with fully powered electrical system. Thank you.

Guys! That was really good, thank you everyone.

I would probably delay lowering the very draggy gear until I was certain I could make the runway.


I agree with that - on this tiny little noteworthy note - is it wind, wind, wind Select gear DN - drop or is it - select DN then wind, wind,
wind - it drops?

I love the dual eng fail ex`s

- especially the loss of 2500` in a 180 turn!

And, don`t forget girls and biys - 280kts!:O

(gives PFL a whole new meaning!):}

Isn't everyone going to die anyway?

With the prospect of good food, nice ladies, partying, a fair salary, a nice new car (I hear the new Mustang is in vogue) shopping in Oxford Street, time out with the kids, touring the Heath, more flights into delectable sunsets, stratosphere existence, travel in your spare time and a beautifully cowardly determination not to die under any :mad: circumstances, coupled with the age old notion of "ALWAYS LAND THE AIRCRAFT!" and NOBODY ON MY FLIGHT IS GOING TO GET HURT LEAST OF ALL THE PAX, NO!. Just for a piddly loss of both engines? You `re gonna be far, far too busy to :mad: die :cool: baby!

[vilas]

Nats
Follow landing gear gravity extension procedure. Crank 3 turns then lever down.

[Chris Scott]

Quote from TyroPicard:
The A320 APU ALWAYS starts from battery power, even with fully powered electrical system.

I think it depends on what is meant by "battery power". But, putting that point to one side, as a statement it's a little unhelpful in that it could be inferred as meaning that the BATs will incur the same discharge whether or not normal AC power is available. Such an inference would be incorrect, as illustrated in my earlier post (http://www.pprune.org/tech-log/486651-airbus-dual-eng-fail-procedure-question-2.html#post8110304). That post can also be misinterpreted, however, so I'll try to clarify what I was describing.

As soon as APU start is initiated, and its starter motor starts drawing current (initially in excess of 800A), the resulting drop of voltage of the BATs is detected. TR1 and TR2 quickly provide over 300A each (exceeding top-of-scale on the ECAM ammeter displays). The combination of current from the two TRs results in the BATs only having to discharge at a (net) rate of about 100A each. That quickly falls as the APU accelerates, reducing the load from the starter motor.

When the rough figures here and in my first post are combined, they provide an indication of the sort of loads that BAT1 and BAT2 have to share if they are starting the APU unassisted on the ramp (in which case ECAM ELEC page will not be available). That is how my estimate of "initially in excess of 800A" is derived.

Airborne, in the case of dual engine-failure (or whatever reason both engine gennies are lost **), and consequential loss of TR1 and TR2, any APU start will equally depend entirely on the batteries. If the RAT is deployed and serviceable, the emergency generator should be powering the ESS TR. However, AFAIK (in the absence of a current FCOM or QRH) the ESS TR can only supply the DC ESS bus (and hence DC ESS SHED). Unlike TR1 and TR2, it cannot supply current for battery charging.

vilas, as one current on type, can you comment on any or all of the above?

** N.B.
Loss of both engine gennies with one or both engines running represents a completely different scenario from the dual engine-fail case, because the maximisation of battery life becomes a top priority.

[sierra_mike]

the ESS TR can only supply the DC ESS bus (and hence DC ESS SHED)you are right Chris. the ESS TR only supplies DC ESS bus resp. DC ESS SHED

http://s17.postimg.org/k6lxng4lb/elec_page.png
ELEC page when EMER GEN running
http://tinypic.com/r/52xfh3/5

[vilas]

Chris Scott
All I can say about the Electrical system is
1. Batteries normally remain disconnected from DC BAT bus.
2. They get connected to DC BAT bus when they need charging.
3. They are also connected when APU master is ON. This is restricted to 3 mts. when in Emergency generator is running.
4. APU starting requires Batteries ON, merely power on DC BAT Bus is not enough. When ground power is supplying the power, DC BAT bus is supplied through DC bus1 but if batteries are OFF APU does not start.
6. In EMER ELEC only Essential buses DC and AC are powered. So batteries do not get charged. They get charged only through DC BAT Bus.
Loss of generators is not a problem because APU GEN can power the AC buses. But without APU it will remain in EMER ELEC.

[Chris Scott]

Thanks for that graphic of the ELEC page on ECAM, sierra_mike.

Hi vilas,

Thanks for that succinct summary. I've just a couple of points.

In (2), as you say, each BAT is connected to its BAT bus (via its BCL) for charging and discharging.

In (6), could you clarify and expand on your last two sentences? I'm not completely sure what scenario you are addressing:
"Loss of generators is not a problem because APU GEN can power the AC buses. But without APU it is same as EMER ELEC without Emergency generator."

[vilas]

I am sorry thats a mistake. What I wanted to say was without generators and APU you will remain in EMER ELEC and Battery life is a back up for EMER GEN loss.

[Uplinker]

With reference to previous posts:

My understanding is that the yellow pump is not designed for continuous operation, (unlike the blue pump), and it will overheat after a few minutes. It's purpose is to assist retraction of the flaps in the event of low yellow hydraulic pressure. It's other uses are for on ground operations: to operate the cargo doors, recharge the parking brake accumulator (on some variants), and pressurise the hydraulics for engineering tests. But it is not designed as a full-time system.

The emergency electrical generator powered via the RAT and Blue hydraulics is of limited size, and therefore does not have enough spare capacity to keep the batteries charged as well.

Why are both these things limited? To save weight and cost. And also because a risk analysis has been applied.


rudderrat: You need hydraulics and an ELAC to control either aileron, (320/321). The right aileron is normally operated by ELAC1 controlling green pressure. If green hydraulics or ELAC1 fail, ELAC2 takes over, controlling Blue pressure.

Chris - your APU start explanation is spot on. A normal APU start is battery assisted, as you imply. :ok:

[Uplinker]

But anyway, guys, let's not get distracted here, the main thing is to be looking for an airfield and landing.

We've got no engines, remember?


:ooh:

[vilas]

Uplinker
If you loose G+Y due to low pressure ECAM will ask you to put yellow electric pump on with PTU OFF to recover Yellow hydraulics. It does not overheat.But Yellow electrical pump flow is only about 1/4 th of yellow EDP so cannot use PTU because it will cause again low pressure on both. Looking for landing field should have been after FLY in NAVIGATE part before application of the procedure.

[Chris Scott]

Quote from Uplinker:
My understanding is that the yellow pump is not designed for continuous operation, (unlike the blue pump), and it will overheat after a few minutes. It's purpose is to assist retraction of the flaps in the event of low yellow hydraulic pressure. It's other uses are for on ground operations: to operate the cargo doors, recharge the parking brake accumulator (on some variants), and pressurise the hydraulics for engineering tests. But it is not designed as a full-time system.

And, in an afterthought:
But anyway, guys, let's not get distracted here, the main thing is to be looking for an airfield and landing.
We've got no engines, remember?

Yes, well remembered! Not much time for any overheat to take place. But, as you've suggested a serious issue re the general use of the Yellow AC Pump, it needs to be addressed, even though it may be off-topic.

Things could well have changed since I last flew the A320 in 2001, and I'm not an engineer. My understanding, however, was that the Yellow AC Pump is identical to the Blue AC Pump. In the event of the a/c being AOG with Blue AC Pump u/s, it's possible to rob the Yellow AC Pump and re-install it as the Blue Pump. (It may be necessary to rotate the pump manifold to a different angle for the fit. The resulting loss of redundancy in the Yellow system would be covered by the MMEL/MEL/DDM.)

Now it's worth remembering that the Blue AC Pump runs continuously during normal ops, being the normal source of Blue System pressure. So - if the two pumps are identical - overheating when installed in the Yellow bay seems unlikely.

Quote:
Chris - your APU start explanation is spot on. A normal APU start is battery assisted, as you imply.

Thanks, but - as I replied to TyroPicard - I guess it depends what he meant by "battery power". In effect, when available, the TRs do most of the work. There's no doubt that the BAT1 and BAT2 PBs must be selected ON for any APU start to function. But where the supply to the APU starter motor is physically taken from is unclear to me, and this is probably not the thread to discuss the matter.

[Uplinker]

Fair enough Vilas, I must have mis-remembered, and now you mention it Chris, I do remember something about pumps being interchangeable.

Perhaps it's the PTU that can overheat?

[vilas]

Uplinker
PTU does not overheat but if PTU is not switched OFF when there is hydraulic Lo LVL then without load it overspeeds causing overheat of the other system leading to Dual Hyd failure. Thats why it needs to be switched of within two minutes in such conditions. Few incidents have happened when Green fluid leaked out when gear was retracted and being in inhibition phase the warning only came later at 1500ft. by then it caused overheat of Yellow system. Airbus has come out with a MOD that inhibits PTU during this phase.

[Uplinker]

Yep, that was it.

Cheers.