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A32X - Two Questions (IRS And HYD PTU)  
User currently offlineCFTOA From Canada, joined Aug 2006, 126 posts, RR: 0
Posted (7 years 4 months 1 week 4 days 8 hours ago) and read 6908 times:

Hello guys  Smile I have two questions, specifically about the Airbus A32X (318-321) series of NB aircraft. I am positive I won't have a problem getting an answer, as I know there are more than a few Airbus pilots on here. Well here goes!

- The HYD PTU (Hydraulic Power Transfer Unit) on the A32X - I understand its purpose, but why on earth is it so loud for? I can only assume that the HYD power transfer unit on similar NB aircraft (IE: 737NG) are almost the same, but why can it not be heard on these other aircraft?

- IRS (Inertial Reference System) alignment, which is done through the MCDU (or mcdoo, as I have heard someone refer to it) takes about 10 minutes I believe. Now my question is, I would only assume that all modern day aircraft use inertial reference systems, seeing as the system relies on the aircraft itself, and no outside system can interfere with its operation - but, on a similar aircraft, like the 737NG lets say, does the IRS have to be manually commanded to align through the FMC as it is on the Airbus through the MCDU? If so, does the time of alignment vary much compared to the 10 minute alignment time of the Airbus? Thanks for your time once again guys  Smile

Cheers,

Tyson McAuley

32 replies: All unread, showing first 25:
 
User currently offlineB78710 From United Kingdom, joined Mar 2006, 341 posts, RR: 0
Reply 1, posted (7 years 4 months 1 week 4 days 7 hours ago) and read 6897 times:

IRS's are aligned using the IRS switches, this starts the (approximate) ten min cycle

some time during this cycle a present position must be entered, through the MCDU as you correctly say! the 10 min cycle is a pretty much standard thing from aircraft to aircraft!

during the ten min cycle the IRU's are measuring 3 things i believe, earths rotation and true north i think are 2 of them, but its kind of slipping my mind at the moment!


User currently offlineB78710 From United Kingdom, joined Mar 2006, 341 posts, RR: 0
Reply 2, posted (7 years 4 months 1 week 4 days 6 hours ago) and read 6881 times:

just re-read your post, to clarify, you dont command them to align through the MCDU......you command them to align with the switch! you enter your present position into the FMC, via the MCDU (MCDU is just the unit/monitor, you use it to enter data in FMC CMC etc)

if you dont enter the present position, the timers will count down to zero, but the IRU's wont' fully align

speaking from experience on 744 and A340's its basically the same principle, just slightly different layout of the FMC


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on the airbus, you can see the switches at the top left of the panel, 3 of them, marked OFF, NAV and ATT

on the boeing, switches are in the same basic area and are marked OFF, ALIGN, NAV and ATT

nav is usualy mode

align on the boeing, i believe is for the purpose of rapid align

and att is used in the event of a nav failure, the IRU's still provide the pilots with attitude data on the PFD


User currently offlineCFTOA From Canada, joined Aug 2006, 126 posts, RR: 0
Reply 3, posted (7 years 4 months 1 week 4 days ago) and read 6842 times:

Alright, thanks for your help - I believe I understand now. So from what I understand, the IRS cycle is activated using these switches on the overhead - now when you say that the IRS position must first be set, I assume you mean by entering the longitude and latitude of the aircrafts current position.. Is this information entered through the MCDU?
thank you for your detailed answer, your help was greatly appreciated  Smile

Cheers.

Tyson McAuley


User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 4, posted (7 years 4 months 1 week 3 days 21 hours ago) and read 6829 times:

The PTU is an Electrically motor driven pump hence the sound.

The IRS on the B752 takes 10 minutes to Align too.The other day we had an APU shutdown while Pushing back & after rectifying the snag,the IRS had to be aligned adding to the delay.

The IRU can be aligned either using the MCDU or FMC.

regds
MEL



Think of the brighter side!
User currently offlineB78710 From United Kingdom, joined Mar 2006, 341 posts, RR: 0
Reply 5, posted (7 years 4 months 1 week 3 days 21 hours ago) and read 6824 times:

Quoting CFTOA (Reply 3):
I assume you mean by entering the longitude and latitude of the aircrafts current position.. Is this information entered through the MCDU?

thats correct yes!

Quoting HAWK21M (Reply 4):
The other day we had an APU shutdown while Pushing back & after rectifying the snag,the IRS had to be aligned adding to the delay.

did the aircraft lose power?

i believe the IRU's are on the hot battery bus arent they? if you drop power with the IRU's still up and running you get a horn sounding to let you know, to prevent draining the battery?


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 6, posted (7 years 4 months 1 week 3 days 21 hours ago) and read 6829 times:

Quoting HAWK21M (Reply 4):
The PTU is an Electrically motor driven pump hence the sound.

The PTU on the A320 has no electric motor. There are two hyd pumps bolted together so one is driven by hyd pressure, and the other one produces pressure. The pump will operate to build up pressure and then stop. The pressure will decay, and the pump will start again. The noise you hear is the pump continually stopping and starting.
The PTU will only run when one of thye green/yellow systems is pressurised and the other is not. i.e. during engine start, and single engine taxi, or when a hyd pump has failed.

Quoting CFTOA (Thread starter):
I can only assume that the HYD power transfer unit on similar NB aircraft (IE: 737NG) are almost the same, but why can it not be heard on these other aircraft?

Does the NG have a PTU? Earlier B737 did not.

Quoting CFTOA (Reply 3):
Alright, thanks for your help - I believe I understand now. So from what I understand, the IRS cycle is activated using these switches on the overhead - now when you say that the IRS position must first be set, I assume you mean by entering the longitude and latitude of the aircrafts current position.. Is this information entered through the MCDU?

When you turn on an IRS it tries to sort itself out. It knows where it was when it was shut down. It can measure how many degrees north or south it is by reading the earths magnetic force. What it cannot do is measure the east or west. You must put this in through a keypad. On modern aircraft you just enter the airport code, and sometimes the stand number, as the lat/long posns are in the FMS.
The IRS then checks your entered position. If it makes sense, it accepts it. If not it will reject it. By entering the position two more times you can force it to accept your position, but it will not accept a false latitude.
You may have typed it in wrong, but the IRS might have been moved. Just towing the aircraft with the power off from one end of the airfield to the other can cause trouble, and occasionally the FMS has an incorrect posn .

There is a lot happening.


User currently offlineB78710 From United Kingdom, joined Mar 2006, 341 posts, RR: 0
Reply 7, posted (7 years 4 months 1 week 3 days 21 hours ago) and read 6821 times:

Quoting TristarSteve (Reply 6):
The PTU will only run when one of thye green/yellow systems is pressurised and the other is not. i.e. during engine start, and single engine taxi, or when a hyd pump has failed

does it operate when you open cargo doors?


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 8, posted (7 years 4 months 1 week 3 days 20 hours ago) and read 6816 times:

Quoting B78710 (Reply 7):
does it operate when you open cargo doors?

No. The yellow electric pump runs.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 9, posted (7 years 4 months 1 week 3 days 20 hours ago) and read 6811 times:

Quoting TristarSteve (Reply 8):
Quoting B78710 (Reply 7):
does it operate when you open cargo doors?

No. The yellow electric pump runs.

OK, when the loaders operate the cargo doors, the yellow electric pump runs. But a solenoid valve also operates so that the main part of the yellow hyd system is not pressurised. The flying controls do not move, and the PTU does not run.

The A320 hyd sytem has always struck me as being a bit odd.
There are three systems Green Yellow and Blue.
Green is press by Nbr 1 engine
Yellow is press by Nbr 2 engine and the Yellow electric pump.
Blue is press by the single Blue elec pump.
The PTU is connected between G and Y and runs when one system is 500psi lower than the other. It can run either way and is always available.
Thats it, except for a RAT in the blue sys.
If only they had put a second elec pump in the Blue system. Because the blue pump runs all the time (it starts automatically on engine start) it has the highest failure rate. It is also not in the MEL, because it is the only Blue pump. We don't hold a spare, so we have to interchange it with the Y elec pump which can be MELd. On your own this takes around 3-4 hours. Small nuts and bolts, no accesss, and when you have both the pumps off, it can take an hour to change all the brackets over as they are different. Off all the jobs I do on an A320, this is the most common. With 4 aircraft a day, we interchange pumps about once a year.


User currently offlineScarebus03 From Ireland, joined Apr 2005, 304 posts, RR: 2
Reply 10, posted (7 years 4 months 1 week 3 days 19 hours ago) and read 6804 times:

TristarSteve,

yes the failure of the blue pump is a pain in the a$$ especially at outstations. In the end we modified all our pumps acc. the latest SB as all the earlier types were failing at about 1,200 cycles. The new type pumps have given us no problems. It would have made more sense for the A320 to have been fitted with the PTU between the green and blue systems and not yellow and green as the yellow already has two power sources. The blue pump could have been used to power the PTU on ground instead of the yellow (although I'm sure it's not as simple as that)
As for the IRS's it's normally 10 mins for aligning on all aircraft, on the A320 series present position can be entered either using the MCDU or the ADIRS CDU which is over the captains head. Present position must be entered within the 10 mins it takes to align the systems.

Brgds
SB03



No faults found......................
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 11, posted (7 years 4 months 1 week 3 days 19 hours ago) and read 6802 times:

Quoting Scarebus03 (Reply 10):
In the end we modified all our pumps acc. the latest SB as all the earlier types were failing at about 1,200 cycles. The new type pumps have given us no problems.

Lucky you. We have a newsheet out to always fit SBd pumps in the Blue system.
But the blue pump that failed on me last month was a new one! The pump was running Ok, but the fan had fallen off and was screeching away, finally tripping the CB after an hours flight.


User currently offlineBoeingfixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 12, posted (7 years 4 months 1 week 3 days 17 hours ago) and read 6784 times:

The only PTU on the 737 is on the NG series. It's for the Auto Slat system, which is normally powered by "B" pressure and uses "A" system pressure to run the PTU if "B" system pressure is lost. The parameters for 73NG PTU operation are:

• system B engine--driven pump hydraulic pressure drops below limits
• airborne
• flaps are less than 15 but not up.

If you hear the PTU, it means there's a problem with the aircraft normal systems.

Cheers,

John



Cheers, John YYC
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 13, posted (7 years 4 months 1 week 3 days 16 hours ago) and read 6772 times:

Quoting B78710 (Reply 5):
did the aircraft lose power

Yes.

Quoting B78710 (Reply 5):
i believe the IRU's are on the hot battery bus arent they? if you drop power with the IRU's still up and running you get a horn sounding to let you know, to prevent draining the battery

The horn sounds after 30 secs if the Bat is supplying power.Its a reminder for the same & lack of cooling.

Quoting TristarSteve (Reply 6):
The PTU on the A320 has no electric motor

Thanks.Not worked on the A320 yet.Was qouting B752.
regds
MEL



Think of the brighter side!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 14, posted (7 years 4 months 1 week 3 days 15 hours ago) and read 6771 times:

Quoting HAWK21M (Reply 13):
Quoting B78710 (Reply 5):
i believe the IRU's are on the hot battery bus arent they? if you drop power with the IRU's still up and running you get a horn sounding to let you know, to prevent draining the battery

The horn sounds after 30 secs if the Bat is supplying power.Its a reminder for the same & lack of cooling.

When you lose AC power, and the horn starts blowing, there is no need to turn off the IRUs at once. In temperate climes the IRUs will happily run off battery power until you manage to hook up a GPU. On some aircraft after 5 mins, one of the IRUs shuts itself down to save power.

It annoys me that some crews turn off the IRUs immediately when the APU Gen fails. It is not necessary.


User currently offlineBond007 From United States of America, joined Mar 2005, 5414 posts, RR: 8
Reply 15, posted (7 years 4 months 1 week 3 days 15 hours ago) and read 6767 times:

Quoting TristarSteve (Reply 6):
The pump will operate to build up pressure and then stop. The pressure will decay, and the pump will start again. The noise you hear is the pump continually stopping and starting.

Yeah, as I've commented before on these pumps, and I am no engineer, it seems to be a poor design (from my limited experience). It just cannot be an ideal solution when the pump is continually switching on/off every few seconds, and from the sound it makes, there is potential for much increased wear.

That aside, Airbus obviously didn't think through the passenger perception of these noises. Since almost every A32x I've been on has taxied out on one engine, all you hear in the cabin is an awful noise ... and numerous pax asking each other "what the heck is that noise". It never sounds very comforting!

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 16, posted (7 years 4 months 1 week 3 days 15 hours ago) and read 6765 times:

Quoting Bond007 (Reply 15):
Since almost every A32x I've been on has taxied out on one engine, all you hear in the cabin is an awful noise ... and numerous pax asking each other "what the heck is that noise". It never sounds very comforting!

If you taxi out with Nbr 1 engine running, and turn on the Yellow electric hyd pump, the PTU will not run.
If you are worried about the noise, it is easy to devise a crew drill to shut it down.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 17, posted (7 years 4 months 1 week 1 day 22 hours ago) and read 6680 times:

Quoting TristarSteve (Reply 16):
If you taxi out with Nbr 1 engine running, and turn on the Yellow electric hyd pump, the PTU will not run.
If you are worried about the noise, it is easy to devise a crew drill to shut it down.

I looked in the BA A320 FCOM last night. We do not normally taxi out with only one engine running.
But the standard drill is to shut down one engine after landing.
The drill is to turn on the Yellow hyd pump, then shut down Nbr 2 engine.
It states that this is to avoid the noise of the PTU running.


User currently offlinePGNCS From United States of America, joined Apr 2007, 2821 posts, RR: 45
Reply 18, posted (7 years 4 months 6 days 7 hours ago) and read 6606 times:

Quoting TristarSteve (Reply 17):
Quoting TristarSteve (Reply 16):
If you taxi out with Nbr 1 engine running, and turn on the Yellow electric hyd pump, the PTU will not run.
If you are worried about the noise, it is easy to devise a crew drill to shut it down.

I looked in the BA A320 FCOM last night. We do not normally taxi out with only one engine running.
But the standard drill is to shut down one engine after landing.
The drill is to turn on the Yellow hyd pump, then shut down Nbr 2 engine.
It states that this is to avoid the noise of the PTU running.

I have seen that procedure on other A-320 series operators, and it works well. Speaking form a pilot's point of view, I really like the A-320 hydraulic architecture, although your comments about the blue electric pump make sense to me. I always thought that the green and yellow systems were tied with the PTU to have maximum redundancy in the brake system, but maybe there are other design reasons at the engineering level that I don't understand.

I definitely prefer the A-320 architecture to the 767 where the gear is on the center system, which in our non-ER aircraft requires electric power to operate (the ADP solenoid requires power to stay open.) I never understood why they didn't put the gear on a system with an EDP, like in the 757. I also don't know why the 757 PTU isn't fully bi-directional. As for the sound in the A-320, the Y Elec pump is the best solution all the way around, but this problem is also present on other aircraft to a lesser extent (DC-9, MD-80, 757) and is pretty much a function of the decision about where hydraulic pumps are located.

This is a great thread. Thanks for all the info!  Smile


User currently offline320tech From Turks and Caicos Islands, joined May 2004, 491 posts, RR: 5
Reply 19, posted (7 years 4 months 6 days 2 hours ago) and read 6585 times:

Quoting PGNCS (Reply 18):
I always thought that the green and yellow systems were tied with the PTU to have maximum redundancy in the brake system, but maybe there are other design reasons at the engineering level that I don't understand.

I suggest the reason for the PTU between the green and yellow systems is to get the landing gear up if the left engine quits on take-off. The blue pump sure wouldn't do it - not quickly, anyway.

There is a shuttle valve in the braking system that automatically changes the brake hydraulics (green - normal, yellow - parking and emergency) if the green system fails. So the PTU isn't there for that reason.

The blue system does operate some of the services (half slats, some flight controls), but its main purpose is to be an independent emergency back-up system. Better not to junk it up with too many demands.

As an AME, I find the A320 hydraulic system to be quite well thought out. The blue system is a bit of a weak link from a line maintenance point of view.



The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
User currently offlineAlias1024 From United States of America, joined Oct 2004, 2755 posts, RR: 2
Reply 20, posted (7 years 4 months 5 days 23 hours ago) and read 6570 times:

Quoting TristarSteve (Reply 6):
On modern aircraft you just enter the airport code, and sometimes the stand number, as the lat/long posns are in the FMS.

Some aircraft also allow you to use GPS to determine the lat/long.



It is a mistake to think you can solve any major problems with just potatoes.
User currently offlinePGNCS From United States of America, joined Apr 2007, 2821 posts, RR: 45
Reply 21, posted (7 years 4 months 5 days 13 hours ago) and read 6532 times:

Quoting 320tech (Reply 19):
Quoting PGNCS (Reply 18):
I always thought that the green and yellow systems were tied with the PTU to have maximum redundancy in the brake system, but maybe there are other design reasons at the engineering level that I don't understand.

I suggest the reason for the PTU between the green and yellow systems is to get the landing gear up if the left engine quits on take-off. The blue pump sure wouldn't do it - not quickly, anyway.

You know, it's been a while since I was on the 320, but I do seem to recall hearing that argument as well, and I appreciate your bringing it up. All in all as an operator, I think the 320 series has a fantastic and well conceived hydraulic system, certainly better than the comparable Boeings.


User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 22, posted (7 years 4 months 5 days 12 hours ago) and read 6527 times:

Quoting 320tech (Reply 19):
The blue system is a bit of a weak link from a line maintenance point of view.

Any reason.
regds
MEL



Think of the brighter side!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4001 posts, RR: 34
Reply 23, posted (7 years 4 months 5 days 12 hours ago) and read 6520 times:

Quoting HAWK21M (Reply 22):
Quoting 320tech (Reply 19):
The blue system is a bit of a weak link from a line maintenance point of view.

Any reason.
regds

Look at reply 9 and 10.
There is only one electric pump in the Blue system, and it must be serviceable.
We keep changing them on the line.


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 24, posted (7 years 4 months 5 days 11 hours ago) and read 6514 times:

Quoting HAWK21M (Reply 13):
Thanks.Not worked on the A320 yet.Was qouting B752

757 PTU is not electrically driven either.

Quoting Bond007 (Reply 15):
Yeah, as I've commented before on these pumps, and I am no engineer, it seems to be a poor design (from my limited experience). It just cannot be an ideal solution when the pump is continually switching on/off every few seconds, and from the sound it makes, there is potential for much increased wear.

The pump is not switching on and off continually. It is surging to meet flow demand and then for lack of a better term idling when there is no demand. The reason it surges and I suspect the reason it is so noisy is because both the motor side and the pump side are constant displacement inline piston pumps. All other pumps on the plane are variable dispacement constant speed pumps and with the exception of the enigne driven pumps (which are located on the engines instead of under the passnger floor) have much less flow capacity and therefor generate much less noise.

Quoting Bond007 (Reply 15):
That aside, Airbus obviously didn't think through the passenger perception of these noises. Since almost every A32x I've been on has taxied out on one engine, all you hear in the cabin is an awful noise ... and numerous pax asking each other "what the heck is that noise". It never sounds very comforting!

As has been said above the pilots can turn on the yellow system electric pump to prevent the PTU form running but they can't hear the PTU in the cockpit so they usually don't think about it. Be glad Airbus put the PTU in the airplane. It's really only meant as abackup for other pumps but when you need it really NEED it.

An interesting side note on IRU alignment. In general the higher in latitude you are the longer it takes for the IRUs to align because of the change in the strength of the magnetic field of the earth at different latiudes which TristarSeve already pointed out.

DL757Md



757 Most beautiful airliner in the sky!
25 A/c train : Hawk21, with the 752 with no engines running, how do you get the flaps and slats up and down quicker?, is it through this electric pump you speak of?,
26 Dl757md : Yep. Just about doubles the flow rate in the left system by using the right system powered by the AC pump. I remember changing a slat PDU on a 757 an
27 Post contains images Bond007 : Well....so kind of then Oh, I'm just commenting on a minor detail I know .... but like I said, I think if the Airbus design guys had sat in the cabin
28 Post contains images SansVGs : The standby pump on the MD-80 makes a similar noise, and gets a similar crowd pleasing response
29 Dl757md : Again I wouldn't blame the design guys. Blame the pilots or whoever comes up with their operating procedures. The PTU is not intended to be used othe
30 Post contains images HAWK21M : You are correct.I got confused. Thanks.i dont know why I said Electric. regds MEL
31 320tech : It's been a while since I've looked it up, but I know there is at least one MEL relating to the blue reservoir air pressure that can be a bit tricky.
32 Troubleshooter : The "low air pressure warning switch" on the blue reservoir has set point slightly higher than the switches on the green and yellow reservoir. If the
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