A319 Barking in Flight
 

As a pax I've often heard the "barking dog" on the A319/320, which I understand to be the power transfer unit running in order to use one hydraulic system to top-up the pressure of the other in case of single engine taxi operations or during startup / shutdown. The other day I was on a flight into Stanstead and the PTU was barking all the way along finals. Why would this be? I would have thought both systems would have been pressurize by the engine-driven pumps during flight?

perhaps there WAS an unhappy dog in the hold!!??

It sounds like they may have had a hydraulic failure of either the green or yellow system.

Absolutely Rick!

The PTU should not run in the normal (as opposed to abnormal) course of events except for a brief self test during the second engine start and on shutdown of the No1 engine on stand if the single engine taxi-in procedure has been used as the No 1 (green) hyd pump (now spooling down) tries to pressurise the yellow system which is no longer pressurised by the yellow electric pump which is switched off immediately before the No 1 eng is shutdown.

Hope that is clear!!

Cheers
mcdhu

I've witnessed the same as PAX, it appears that for some magic reason the PTU sometimes also kicks in when the gear comes down even though the a/c is absolutely fine.

I've heard the barking dog on finals when positioning/pax in A319s on many occasions and pax often comment on it as they are getting off. I am uncertain of the logic behind the PTU activation, but one of its many uses is to maintain hydraulic pressure in both systems in the event of engine failure, so having it running during critical phases of flight is not a bad thing!

It is certainly not inhibited from running during flight (unless you have turned it off:ooh:) but it will activate if it senses a differential pump pressure of 500psi, so caused by extension of landing gear perhaps?

Absolutely. Landing gear actuation will routinely activate the PTU for a couple "barks" as the aircraft uses one hydraulic to help the system under very high demand.

This wasn't a couple of barks -- it was all the way along final and to the ramp.

...........in that case, something was wrong!

Cheers
mcdhu

Can the PTU be manually switched ON on the A319.I presume it can.Looks like it was needed,probably due hydraulic snag on a system.
regds
MEL

Only indirect. You can switch off one Hydraulikpump to cause the PTU to start. For the PTU self there is only an Auto/Off switch...

Greetings

Capt Obvious here, but did u check your HYD page? What was going on there?

Sounds like a fault I have encountered. You can dispatch with the PTU continuously operating as long as the PTU is checked to be operational in both directions before the 1st flight of the day. It would be more noticeable in the cabin during approach at low speed & reduced power.

Any of you guys able to offer an explanation for the 'barking' being reported from the cabin crew taxiing out to the holding point for t/o? Hydraulic system page checked, all normal and PTU shown to be not running.

PTU Indications
 

If memory serves, the PTU indications are based off the pump and system low pressure switches,rather than a position pot on the PTU control valve, but the hydromechanical bit opens the valve when you have 500psi differential pressure (as noted above). If you get the chance, grab an AMM and have a look at the indication sections.

So a suggestion to what could be occuring: during flap/slat extension and controls checks, and low engine RPM, if you drop (for example) you could (theoetically) get the presure dropping low enough for the PTU to pop in without the system dropping low enough to trigger the indications.

This 'barking' sound is a regular occurence on bmi's A319's. The whole of the taxi to the runway, if it's a single engine taxi, that noise is pretty loud in the middle of the cabin. Also as mentioned on final approach on most flights this also happens. The pax must wonder what the hell is going on, it's not exactly a quiet noise!!

I don't think pax have access to the HYD page.................:ok:

I think we pax should have access to ALL the FMC pages. Those games on the seat back are just too damn boring.:)

Possible sequel to 'Snakes on a plane' ....

'Barking Dogs on a plane' starring Scoobie Do!:)

Tell bmi that if they single engine taxi on No1 and turn the yellow electric pump on, that should stop the dog barking...:=

quiet noise!!??

hmm...

[quote]Tell bmi that if they single engine taxi on No1 and turn the yellow electric pump on, that should stop the dog barking...:=[/quote[

Now SOP at EZY by the sound of things...no barking on recent late sectors EGAA-EGSS :)

That is exactly what we do and have done since we introduced single engine taxi out.

Having flown in various Airbii (pax) and never having noticed the barking, and never having heard of a PTU, I had a bit of a Google and came across this site/ | Ozten Network Home | Aviation site :)

Two things- It informed me that a PTU does not actually transfer hydraulic fluid, so can anyone enlighten me as to how it works (in layman speak) :confused:

The other thing is that while the site is in, I believe, Turkish, all the articles / info sheets are in English. If I study hard and find a kindered soul who will let me have a go in an A320 simulator, will I be able to fly the thing? :}

Maxbert

Maxbert

In (I hope) laymens terms. a PTU uses hydraulic pressure from 1 system to drive a transfer shaft. The non pressurised system has an impellor in it which thereby pressurises the second system with no fluid transfer between the two systems.

An analogy would be hydro electric power - water under gravity (in this case hydraulic fluid at 3000psi) drives a shaft which turns a turbine (in this case an impellor sitting in the hydraulic line) generating electricity (in this case hydraulic pressure). There is no mixing of input and output sources.

HTH

PTU.
Power Transfer Unit is an hydraulic motor driving an hydraulic pump mounted on a common shaft.
The ones on Airbus are one way only but the ones on the DC10 are called Reversable Motor Pumps and can work either way.
Hope this helps.

TopBunk, dixi, many thanks!

From my reading, Airbus A319 / A320 seem to have such a device, is it not common to all A/C in one form or another?

Maxbert

PTU.
Power Transfer Unit is an hydraulic motor driving an hydraulic pump mounted on a common shaft.
The ones on Airbus are one way only but the ones on the DC10 are called Reversable Motor Pumps and can work either way.
Hope this helps.

PTU and RMP´s are the same thing

Wasn't scraps a boy dog?:E

Wirelock.

The PTU's on the A300 are not reversable.

ie. Green system can power Blue or Yellow but not the other way around.

I'm not sure about the later Airbus types.

On the A320 family the PTU allows the yellow system to power the green and vice versa.

I've said it once, and I've said it a hundred times.................

We need a permanent "Sticky" for "Strange Airbus noises and other things that go bump in the night!":ok:

Moderators please note!:ugh:

Regards,

Old Smokey

I once had a positioning colleague enter the flight deck after landing, asking if everything was alright, because he heard the PTU barking continuously during the whole approach.

Also heard similar comments from cabin crew on a different flight, with a different A319 aircraft.

On both occasions there were absolutely no indications of any hydraulic problems in the flight deck. So the PTU seems to be running a0t times without any indication to the pilots. I haven't seen that explained yet ;)

Dunbar & Ground Star - We certainly don't taxi single engine with the yellow elec pump off! We are not Muppets.:D

why the ptu runs!!
 

The PTU is made up of a variable displacement unit coupled to a fixed displacement unit. The variable displacement unit is connected to the yellow hydraulic system. The fixed displacement unit is connected to the green hydraulic system. Displacement of the variable displacement unit is varied to maintain the required running and breakdown pressure differentials between systems. Displacement of the variable unit is controlled by means of a control which senses the system delta pressure.
The variable displacement unit is at maximum displacement during the power transfer from the Yellow to the Green system. Then it is at minimum displacement during the power transfer from the Green to the Yellow system.
The variable displacement unit includes a hydraulic servo valve and a variable cam. The servo valve gets input from the pressure differential, which starts the PTU.

if the servo valve malfuctions it is possible for the ptu to operate without an ecam indication on the flight deck

hope this helps

some more info

to display the G to Y PTU ECAM indication, it is necessary to have the condition Y sys press

lower than G sys press by more than 200psi. This condition is not required for the display of the Y to G

PTU ECAM indication. So, as soon as the Y EDP is selected off, the PTU starts faster than expected

and therefore the Y sys press has no time to droop the pressure.

This is apparent in the ECAM logic manual