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?