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A320 STRANGE PTU behaviour

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A320 STRANGE PTU behaviour

Old 24th Jan 2013, 04:31
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A320 STRANGE PTU behaviour

please see these videos
Barking Airbus A320 on Finals into AMS - YouTube
Easyjet Takeoff with PTU fault - YouTube

There is no engine failure, no ecam,no ptu fault, or gear/slat/flap config change, to make the ptu run.BUT why is it running continuously without any action from crew!
Acoording to ptu logic, the only times it comes in are during 2nd engine start as a self test, if you do a single engine taxi and you start or shut down your eng1 on taxiway, and after landing gear retraction, but definitely not at VR, which would mean your flight had experienced an ENGINE FAIL at VR, nice scenario for a sim sessin though.
This is CERTAINLY abnormal case. remember from cockpit PTU running is barely audible and you can confirm it only by memo 'HYD PTU'. ptu logic prevents it from running in case of hyd reservoir low level, low pressure, ovht, pump low pressure. in a320dlh's video notice how the freq of barking increases on grnd spolier deflection on touchdown!!
in the second video, the pnf could have easily seen ecam memo of hyd ptu, and if in case the ptu was indeed faulty and running for at least 2 mins continuous, no pilot intervention can lead to dual hyd failure in worst case scenario by hyd ovht from yellow to green. just reach up and press that thing OFF, or return to the gate.
Guys, we need to solve this,"out off FCOM stuff". Any A320 AME here in forum?
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Old 24th Jan 2013, 10:09
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Hi EIU_EEC,

Not an AME, I’m afraid: just an 11-years-retired A320 pilot. Flying as passenger several times a year, I get to hear the PTU from the cabin almost as much as when I was working. So, just a few thoughts.

(1) Are you sure the PTU could overheat either the Green or Yellow fluid in as little as 2 mins?

(2) On both clips, the PTU is running only at a low height or on the ground.

(3) In the AMS landing, PTU starts at about 300ft, long after the flaps and L/G have been fully extended, and in the apparent absence of roll-spoiler or other flight control movement, except (possibly) the THS. As you say, it continues throughout the landing run. The increased noise during ground-spoiler and engine-reverse extension seems logical.

(4) In the easyJet take-off, it runs throughout taxiing and the take-off run. From start of take-off until rotate, the loads on the hydraulics are minimal. It stops 5 secs after lift-off, at which point the L/G would normally have started to retract. 10 secs after lift-off, the “ping” from the No-Smoking sign relay confirms that L/G retraction is complete.

(5) I wouldn’t expect the PNF to notice the Memo “HYD PTU” in the air at low height, but would certainly agree that it should be noticed eventually while taxiing. However, if there is a software fault, can we assume that the message will appear? I don’t know precisely what generates that message.

(6) Seems silly to ask, but could there possibly have been a mod to the PTU operation criteria? If not, this is a behaviour that needs to be explained.
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Old 24th Jan 2013, 10:32
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Sorry buddy you but you are sadly mistaken, the PTU will not overheat a system when both reservoirs have hydraulic fluid.

The problem happens when one system is empty while the other system is operating the PTU to pressurize the empty system. Since there is nothing tompressurize the PTU will "overspeed" and overheat the full system, leading to a dual hydraulic loss due to overheat.
This problem will be masked by landing and takeoff inhibit. above 1500ft on t/o the ecam will display instructing to turn off the ptu.

This can happen in both directions, green to yellow or yellow to green.

When an engine is shutdown the PTU will operate for far more than 2 minutes. The airbus has no electrical hydraulic pumps (only engine driven, yes there is a yellow electrical but that is not used normally for pressurizing the system in case of engine driven pump failure), so the PTU will pressurize the remaining system.

And it will do so happily for ages and ages without overheating the systems.

There is no danger in these videoclips.

In addition easyjet airbusses have been modified to display an empty reservoir ecam around 400ft on t/o.

Last edited by 737Jock; 24th Jan 2013 at 11:22.
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Old 24th Jan 2013, 11:53
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737jock, My question was, Why is the PTU running when it shouldn't in the first place?
Hi, chris, you could reason out any clue Why it is running?

Last edited by EIU_EEC; 24th Jan 2013 at 11:55.
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Old 24th Jan 2013, 12:40
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Originally Posted by EIU_EEC
737jock, My question was, Why is the PTU running when it shouldn't in the first place?
No, the only questionmark in your post was in:
Originally Posted by EIU_EEC
Any A320 AME here in forum?
737Jock gives you some good hints in conjunction with the overheat.
Instead of thanking him for helping you, you bark at him.
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Old 24th Jan 2013, 12:56
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In our company, when we taxy in, we shut down engine 2 after its cool down period. Before we do this we start the APU (to replace the genny) and start the Yellow Electric pump. So no need for PTU to run.
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Old 24th Jan 2013, 12:59
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Okay! My question is why should the ptu run in these two videos?
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Old 24th Jan 2013, 13:13
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Hmmm...

Don't know. It does not seem normal to me.

The PTU works when difference between the hyd pressure is more than 500 psi in either direction, (from memory). It is normally heard on engine shutdown, and as has been said; during a test phase on engine start.

Easy taxy in and out on one engine, so the PTU might be heard then if they don't use the Yellow Electric pump. But on Take off??

Without knowing the answer, I would have to guess that a HYD pump was giving low pressure, or the PTU 500 psi sense was up the bucket.
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Old 24th Jan 2013, 15:05
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Possibly single engine taxiout, followed by a PTU self test after the second-engine start. I believe the PTU self test can last up to 2 minutes.
Shouldn't happen during T/O but no harm either. I would put it down as a glitch (not even a fault) in the ptu selftest system.

Last edited by 737Jock; 24th Jan 2013 at 15:25.
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Old 24th Jan 2013, 16:28
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For what it is worth, I have noticed it a few times now while being passenger and I asked the drivers after landing whether they had done OETD which they hadn't. It made me wonder.
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Old 24th Jan 2013, 18:45
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As a regular commuter and Airbus pilot I do occasionally hear the PTU running as a passenger without any obvious cause. In the beginning I used to ask the flight crew what was going on, if they had any hydraulic problems or if they knew the PTU was running all the time, only to be met by blank stares from the pilots. Apparently there is no obvious indication in the cockpit that the PTU is running on these occasions.

So I have no answer to this question, I can just confirm that it DOES happen.
It usually happens after engine start and during taxi, it stops once airborne with the gear up, only to start again on approach when the gear is lowered. Or sometimes only during taxi or only on approach.

An Airbus mystery!
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Old 24th Jan 2013, 18:59
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Sounds like an MEL item. I had this a few years back.

"PTU may continuously run when set to AUTO provided that the operation of the PTU in both directions is checked before the first flight of each day."
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Old 24th Jan 2013, 19:27
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EIU_EEC,

Sorry, but I don't think I can shed any real light on this one, particularly as I'm retired. In addition to giving you a hard time (while in one case referring to you patronisingly as "buddy"), several posters seem to have missed the original point of your thread completely. (Wasn't it ever thus? )

In the case of the landing at AMS (in marginal Cat 1 conditions of cloud ceiling, so it might be an autoland), I can only point out that we cannot rule out the possibility of a Green or Yellow system low pressure causing the PTU to start. I've run the video again.

2:16 before touchdown (video time 0:04), there is that "ping" (chime) associated with the No Smoking signs automatic illumination (yes, I know that the crew overrides the automatics by forcing the signs on throughout the flight, but that doesn't seem to stop the chime associated with L/G position). So the L/G is being extended at that stage, as is normal (~1500ft agl).

Flaps 3 seems to be extended 1:42 before touchdown (video 0:38), and Flaps Full 10 seconds later (for that, the T/E flap motors are clearly audible). T/E flaps use Green and Yellow, IIRC, but these flap selections have not provoked PTU start.

The PTU starts 15 secs before touchdown (video 2:06), so that's about 170'R (170ft agl), and continues at least to the end of the landing run.

Unless there was a low-pressure trigger (genuine or false) for the PTU to start at that point, I can only speculate again that there might be a recent change to the PTU operation logic? For example, what about an autoland, using both APs?

Turning to the easyJet take-off, Uplinker and 737Jock are working on the single-engine taxi theory, which sounds likely. If the PTU self-test lasts up to 2 mins after the second engine start, is there a minimum time between engine start and commanding take-off thrust on the CFM-56?

Right Way Up,

Only just seen your post. Sounds like a fail-safe logic in that, if the differential-pressure sensor fails, the PTU runs continuously?

Not good for the SLFs down the back. I've always wondered (since 1988) why this PTU (the Yanks call them RMPs - reversible motor-pumps - on other aircraft I've flown) is so damned noisy in the A320 cabin...

Last edited by Jetdriver; 24th Jan 2013 at 19:53.
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Old 24th Jan 2013, 19:34
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Yes, the minimum time is 2 minutes.
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Old 24th Jan 2013, 19:39
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Thanks for that, ECAM Surprise. (Thank goodness YouTube didn't exist in my day....)
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Old 24th Jan 2013, 21:01
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A320 STRANGE PTU behaviour

737 jock, it's not the ECAM inhibit that has been modified to present a HYD SYS LO LVL on the ECAM below 1500ft/2min after lift-off. The PTU inhibition logic mod has been applied to all ezy airbuses. This means that the PTU will not run when either HYD SYS LO LVL to protect against an inadvertent overheat due to PTU overspeed as you stated.
Getting back to the OP. I have found the PTU to run many times as described, albeit not continuously. Surely the 'AUTO conditions to run' were not met at this time. I attribute it to a 'glitch' as you said and nothing to worry about when all other indications/ops normal.

ATB
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Old 24th Jan 2013, 22:17
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OPEN DES check the warnings and cautions section:

The "modified" ones inhibit the RSVR LO LVL for the first 15seconds of flight phase 5, whereas the other ones inhibit up to 1500ft/2min.
I imagine that 15sec will be approximately 400ft, where we can start ecam drills.

Not sure if it is part of the modification, but it seems to be as it is across the entire board of airplanes. But the majority inhibits only for 15 seconds.

Anyway thanks for the information, had tried to find it but couldn't find a ref to the Modification. And I still can't find it, any idea?

Last edited by 737Jock; 24th Jan 2013 at 22:24.
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Old 25th Jan 2013, 03:09
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In addition to giving you a hard time (while in one case referring to you patronisingly as "buddy"), several posters seem to have missed the original point of your thread completely. (Wasn't it ever thus? )
Chris, thank you!
In summary, till now the reason for the "glitch" hasn't been understood. ptu self test for 2 minutes...and that too in the air in the LVO ops..
This is from the MEL if it helps in getting some clues.

Note: 1. The PTU pressurizes the system to a nominal value of 3 000 PSI PSI (± 200 PSI),
but if no consumers are operated the pressure is not constant. The PTU operates in
a cycle which keeps the pressure in the hydraulic systems between 2 100 PSI and
3 200 PSI.
2. For passengers comfort, the PTU may be set to OFF during the taxi after landing
provided that both engines hydraulic pumps are operative and running. The PTU must
be set back to AUTO before leaving the aircraft.
Can this lead to the PTU servo valves in an endless loop?

The fact is THIS very occurrence is being dismissed as harmless glitch, already in 2 different cases is very disturbing. In aviation NOTHING can be dismissed as unimportant till we get hold of the root cause.History shows this very attitude of us pilots of thinking we know everything and nothing can happen to us has led to the deaths of thousands of innocent lives, who have no idea of whether its a PTU or a dog loose in the Aft cargo barking away!
So guys instead of criticizing everyone's small errors, please behave constructively and seek help from maintenance ASAP!

Last edited by EIU_EEC; 25th Jan 2013 at 03:22.
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Old 25th Jan 2013, 03:57
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Quoting 737Jock[

The airbus has no electrical hydraulic pumps
I thought the blue system was electrically powered?
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Old 25th Jan 2013, 04:05
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There is no danger in these videoclips
737jock are you doubly sure of this??? unless you pinpoint to me the reason.
ptu self test, SET, etc,are all but guesses.
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