A320 STRANGE PTU behaviour
No problem IFix - we all have our bad days. Apology accepted; I will remove my reference to it 
Chris; yes, that is exactly what I am refering to; The accumulator smooths pressure fluctuations (and covers short term pressure drops as Ifix says). If an accumulator had lost its nitrogen charge, I thought any pressure fluctuations in the HYD system might trigger the PTU just for a moment, each time, causing the 'barking dog syndrome'.
Not being an aircraft engineer, I don't know what the maintenance procedures are, but no we don't have any cockpit indication of accumulator pressure, so this might go undetected until the next hangar visit?
Chris; yes, that is exactly what I am refering to; The accumulator smooths pressure fluctuations (and covers short term pressure drops as Ifix says). If an accumulator had lost its nitrogen charge, I thought any pressure fluctuations in the HYD system might trigger the PTU just for a moment, each time, causing the 'barking dog syndrome'.
Not being an aircraft engineer, I don't know what the maintenance procedures are, but no we don't have any cockpit indication of accumulator pressure, so this might go undetected until the next hangar visit?
Last edited by Uplinker; 31st Jan 2013 at 12:43.
I started the second engine the other day with the hydraulic page up on the SD, just out of interest sparked by this discussion - and watched the PTU cycle on as the second engine master was selected on.
I can't say I have ever noticed a PTU message on the memo during engine start before (but I can't say I have looked for it, either.)
I can't say I have ever noticed a PTU message on the memo during engine start before (but I can't say I have looked for it, either.)
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PTU Operation
Please take your time to read this doc. http://rgl.faa.gov/Regulatory_and_Gu...E/NM-13-03.pdf
It is well known that the PTU operation is automatic, it will start working whenever a 500 psi differential pressure exist btwn green and yellow hyd sys, it will be inhibited at first engine start and during cargo door opening among other details (considering parking brake position, and NW steering bypass lever position)
The real problem comes out when there is a leakage on green or yellow hyd system, if you let the ptu working for more than two minutes it will produce an overheat condition in the operative system.
Please check the link above...
It is well known that the PTU operation is automatic, it will start working whenever a 500 psi differential pressure exist btwn green and yellow hyd sys, it will be inhibited at first engine start and during cargo door opening among other details (considering parking brake position, and NW steering bypass lever position)
The real problem comes out when there is a leakage on green or yellow hyd system, if you let the ptu working for more than two minutes it will produce an overheat condition in the operative system.
Please check the link above...
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Pax here - was intrigued this morning by the PTU running continuously during taxi (OK) but also without interruption until ~30 seconds after takeoff. Easyjet, 1st flight of the day (I suppose!).
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My operators' QRH had an OEB for a while directing the PM to IGNORE ECAM and follow the QRH procedure.
As far as these videos are concerned; there was a detected 500 PSI difference between the 2 systems, and the PTU operated per design. Either an EDP/accumulator wasn't functioning properly, or the pressure sensor was incorrect...
To the poster who said there aren't any electric pumps on the A320... Except on the Blue System and the Yellow System...
Anyway, my guess would be the electric hydraulic pump in the yellow system running. This is done when single engine taxiing, but should be selected off when the second engine has started, before take-off.
If it was the yellow pump, perhaps the crew got distracted and missed turning it off before take-off, then spotted it after getting airborne?
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@Uplinker yes, I am reasonably sure. Where I wrote "continuously" I did mean "continuously pulsing" ("of course"). I did record the sound, rather low quality, starting when we were lining up for t/off ... attached here as .amr.zip
That file won’t download for me. Sorry, I don’t know the answer. The only reason I can think of if the PTU was running after the second engine start is a faulty PTU or low pressure in the green or yellow hydraulic systems. But any of those are a no dispatch item.
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But technically, assuming that a non-normal condition "a no-dispatch item" was only detected after (single-engine) taxiing has started, then it could pe possible to continue? For example if a problem was only detected during or after 2nd engine start?
By the letter of the law, perhaps. However, I for one would not take-off with a known hydraulic problem that was a ‘No dispatch’ item in the MEL.
It must have been something else in this case. I wonder if a faulty hydraulic accumulator could have been the problem? This has been discussed on Pprune elsewhere, and might occur too briefly to bring up a fault indication on the flight deck.
It must have been something else in this case. I wonder if a faulty hydraulic accumulator could have been the problem? This has been discussed on Pprune elsewhere, and might occur too briefly to bring up a fault indication on the flight deck.
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May I revisit this thread with another query about the PTU.
If I am not mistaken, the distinct sound of the PTU can be heard when the landing gear is retracting and extending. There are also a lot of videos on YouTube taken in the cabin and the PTU can be heard when the gear is in the process of being retracted or extended.
Is the PTU working during landing gear operation? I don’t remember ever seeing “HYD PTU” on the ECAM Memo for this, but that’s not where I am usually looking during those times anyway.
If I am not mistaken, the distinct sound of the PTU can be heard when the landing gear is retracting and extending. There are also a lot of videos on YouTube taken in the cabin and the PTU can be heard when the gear is in the process of being retracted or extended.
Is the PTU working during landing gear operation? I don’t remember ever seeing “HYD PTU” on the ECAM Memo for this, but that’s not where I am usually looking during those times anyway.
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Can't see any ground hydraulics plugged in, so guessing they're just using the yellow pump for this test swing. Landing gear is on the green system (if my memory serves me right - It's been 6 years!), so without the left engine running, the PTU has to be used to retract the gear.
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Thanks Cough.
What about under normal LG retraction and extension? For example in this video at 1:53 you can hear the PTU (unless that’s something else) during gear retraction. The same can be heard for gear extension quite often and I’ve heard it before as a passenger as well though you typically got to be seated at rows close to the landing gear.
What about under normal LG retraction and extension? For example in this video at 1:53 you can hear the PTU (unless that’s something else) during gear retraction. The same can be heard for gear extension quite often and I’ve heard it before as a passenger as well though you typically got to be seated at rows close to the landing gear.
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I can only guess dream. Typically during landing gear extension the landing gear is often dumped at the same time as some flap/slat which puts a load on the green system. The PTU jumps in if the pressure differential exceeds 500psi between the two systems, so I could only summarise that if the yellow is running at a slightly higher pressure, green drops a bit when the services are called for then you get a few moments of PTU. End of the world? I dunno, not an engineer, but I guess not. Like you I've never seen HYD PTU either, more things to look at!
All the hydraulic systems have multiple accumulators to smooth out the pressure delivery. Accumulators also assist the main pumps by supplementing the system pressure when a large demand is made - such as the landing gear being moved.
If the accumulators are leaky, or not charged with the correct nitrogen pressure, the Green Hyd pressure might well momentarily drop below the PTU triggering pressure during gear movement, or indeed multiple demands, so it cuts in briefly to help.
In the cabin one can certainly hear the PTU blipping on very briefly in some aircraft during gear deployment. I don't think one or two second's operation is long enough for an ECAM memo to be triggered though?
If the accumulators are leaky, or not charged with the correct nitrogen pressure, the Green Hyd pressure might well momentarily drop below the PTU triggering pressure during gear movement, or indeed multiple demands, so it cuts in briefly to help.
In the cabin one can certainly hear the PTU blipping on very briefly in some aircraft during gear deployment. I don't think one or two second's operation is long enough for an ECAM memo to be triggered though?