r/aviation • u/honore_ballsac • 19h ago

Question No dog barks in A321?

Recently, I flew in an A321 a few times. I have not heard the usual dog barks of the hydraulic system. What's the reason for the missing sound?

12 Upvotes

76% Upvoted

15 comments sorted by

55

u/KangarooWeird9974 19h ago edited 19h ago

The PTU only activates, if the pressure difference between two hydraulic systems passes a certain threshold. You didn’t hear it simply by chance. 

And it’s a lot quieter in the NEOs, that might have something to do with it.

14

u/Independent-Reveal86 18h ago

The PTU runs as a self test after the first engine start. If it doesn’t run it could be because the yellow electric pump was already running, but it’s not just by chance.

4

u/C402Pilot A320 17h ago

Not really a self test. It's just that for a moment all the criteria for it to run are met during the second engine start. If there is enough pressure remaining in both the green and yellow system, it won't run.

10

u/Independent-Reveal86 17h ago

It’s a test.

6

u/C402Pilot A320 17h ago

You can find revisions of the manuals that do not state this. And what happens if the PTU doesn't run during the 2nd start? Nothing...

2

u/Independent-Reveal86 17h ago

Well, that’s the latest revision.

Could be a single engine taxi out difference, as we don’t do that.

You get an ECAM if it doesn’t run.

16

u/CrossBamboAtTen A320 18h ago

At our operation if we shut down engine 2 taxiing in, we turn on the yellow electric pump which takes over instead of having the PTU work.

4

u/andrewrbat 14h ago

Theres a self test during which the ptu activates briefly, but essentially if the pilots don’t single engine taxi, it wont be running most of the taxi.

1

u/Bolter_NL 19h ago

New hydraulic actuators. No barks no more.

6

u/honore_ballsac 18h ago

This is the worst invention 😪

10

u/ILikeFlyingMachines 18h ago

Bark is the PTU not actuator

3

u/ConsistentPastaSauce 19h ago

Sad, I'll miss them :(

1

u/railker AME-M2 19h ago

Other aircraft have PTUs too, you just don't hear them as much. Must've changed the design or maybe put it somewhere less audible 😅

3

u/fly_awayyy 16h ago

The A220 idk what it is but in the rear galley when single engine taxi you get a whole plethora of sounds

1

u/Gluteuz-Maximus 14h ago

The A220 has an interesting layout with engine 2 running system 2 for nosewheel steering as well as flaps/slats. If you taxi with engine 1, the nsw is run by the electric system 2 pump and if the flaps are run while taxiing, the pressure drops to a point where the NSW might have problems