View Full Version : A319 PTU running during taxi out.

28th Jun 2018, 06:51
Hello guys,

Few days ago, I travelled as a passenger from Chengdu to Lhasa on an A319.
Was quite interesting to see things from the cabin in a different airline: Sichuan Airlines.
One thing really puzzled me: During engines start, I noticed PTU was running for few seconds then stopped as normal. But then just when the aircraft started to taxi out, PTU kept running all the time until take off power was applied?! And both engines were running for taxi. Is there any failure which require an operational procedure to run the PTU during taxi out?
Today I flew again on A319 from Lhasa to Chengdu and they did not run the PTU during taxi.
Fun fact also, I noticed PTU runned for 2 seconds during gear up and gear down transition. Never noticed that before. Probably because of the temporary drop of pressure of the green system.

Bonus question: Lhasa airport is at 11700 feet. Do you know if the crew applied a specific procedure?
And A319 is normally operating to airport up to 9200 feet maximum.To operate higher do they have more powerful engines?

Thank you.

Pugilistic Animus
30th Jun 2018, 05:05
Hi Pineteam...does PTU mean, like on the 757 (Power Transfer Unit) ?

30th Jun 2018, 05:16
Hello Pugilistic Animus,

Yes it does. Unbelievable that they use the same terminology for once isnít it? xD

30th Jun 2018, 15:32
And A319 is normally operating to airport up to 9200 feet maximum.To operate higher do they have more powerful engines?

A319 in particular is favored for high-aiport operations. Probably because they do have the same wing as an A320, and may have equal engines, but have lower operating weights. Does require special certification of craft and crews.

Airbus offers a high-altitude package (cockpit switch enabled) which changes things like the "low cabin altitude" pressurization warning altitude and dropping of cabin pax masks, which normally alerts at 10000 feet. And training in the other issues involved

Another issue is higher TAS on landings and takeoffs - you get closer to tire speed limits. And non-aviation issues (altitude sickness, either among crew or pax)


The A319 excels in operations from high-altitude airports (http://www.airbus.com/newsroom/news/en/2005/02/the-a319-excels-in-operations-from-high-altitude-airports.html)

Pugilistic Animus
1st Jul 2018, 05:26
Alas, they both are using mechanical engineering terminology...'PTU's 'Turbomachinery" etc...they both decided to use the engineering terminology for one thing.

Escape Path
8th Jul 2018, 01:17
If I'm not wrong, the PTU runs for a bit during the 2nd engine start for testing purposes. So that should cover the first escenario you heard it in. As for why it was running during taxi out with both engines, beats me! I've heard it run during SINGLE engine taxi when the crew forgets to run the Y elec pump, but that's about it.

Iīve heard it go at gear up and down too, but never payed too much interest to it, so I don't have an answer for that either. But yours sounds logical. Though I think the drop is not for enough time to trigger the PTU?

8th Jul 2018, 05:05
There is a TFU ( which deals with this problem.
It is a combination of special PTU issues and green/yellow hydraulic system issues.

30th May 2019, 03:41
The PTU should not be running during 2 engine ops on taxi out if the G and Y Hyd sys are operating normally.
it is triggered to work automatically when the sys pressure difference between these 2 are greater than 500 PSI.
Without being a mechanic I would say something was not operating normally if both engines were indeed running and if the PTU was still barking.
Single engine taxi and forgetting to turn on the Y electric hyd. pump would trigger it to work until you set the parking brake.

4th Jun 2019, 11:43
When a passenger on A320 family, you always hear PTU running to assist when the gear is moving. The gear is a very heavy user* and causes a big demand on the engine pump.

After shut down you can sometimes hear the PTU ‘see-sawing’ in one direction then the other, as the Green and Yellow pressures bleed down.

* As a matter of interest; have you noticed how short the lever arm is that the retraction jack pushes on to raise the mains? The mechanical disadvantage of that must be insane. Imagine trying to swing the weight of the main gear up by pushing on that lever so close to the pivot. It must present a HUGE load to the retraction jack - hence why it is such a large diameter jack - and I am not surprised that the Green system needs some help with it !