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...:=