The barking dog on Airbus 320 ✈️ location The Airbus A320 Power Transfer Unit (PTU) is a mechanical device that transfers hydraulic power, not fluid, between the aircraft's green and yellow hydraulic systems to maintain pressure when one system is low, preventing fluid transfer and creating the famous "barking dog" sound, especially on the ground when one engine is running and the other system is idle. It activates when the pressure difference between systems exceeds about 500 PSI, ensuring back

PTU — Power Transfer Unit — makes a loud, rapid “woof-woof-woof” / barking noise when it operates. Crews and ramp workers started calling it the “barking dog” long before it ever made it into training slang. Here’s what’s going on: What the PTU does The PTU connects two hydraulic systems (e.g., Green and Yellow on Airbus) It transfers power, not fluid If one system has pressure and the other doesn’t, the PTU kicks in to balance things Why it sounds like a dog The PTU is a hydromechanical device