If you’ve flown on a local airline in the Philippines, there’s a high chance you’ve flown on an Airbus A320. During your flight on the A320, you may have noticed a unique barking dog sound the aircraft makes before takeoff and after landing. Although this noise may cause some passengers concern, it is not a cause for worry. However, it’s worth understanding why this sound occurs.
The A320 is one of the most popular narrow-body jets, with more than 5,000 built and 8,000 more on order. It is wider than its competitor, the 737, and is equipped with a side stick instead of a yoke, fly-by-wire technology, and a fold-out tray table in each crew position. But despite these features, it still produces an unusual sound.
Power Transfer Unit
The barking noise is made by the PTU, or power transfer unit. The PTU transfers power from one hydraulic unit to another, and the A320 has three hydraulic systems. Two are powered by each engine, while a third system is powered by an electric backup pump. The PTU provides hydraulic power across the systems, which is used in flight to power the control surfaces, landing gear, nose wheel steering, braking system on the ground, and movement of the flaps and slats.
The barking noise is most commonly heard when the aircraft is departing from the gate or after it has landed and one engine is shut down. This is because typically only one hydraulic system is running, and the system is utilizing the PTU to ensure that the entire hydraulic system stays pressurized.
An Important Component
Despite being annoying for some passengers, the PTU is a valuable system that ensures pilots have access to all controls at all times. The barking noise, which has been likened to a buzzsaw or high-pitched whining noise, is caused by a hydraulic pump.
According to Airbus, the A320 hydraulic system is composed of three independent circuits: Green, Yellow & Blue. The users are shared between the systems to ensure the control of the aircraft even when one system is inoperative. On the blue hydraulic system, the normal source of pressure is the electrical pump, and the auxiliary source is the Ram Air Turbine (RAT). The Constant Speed Motor/ Generator (CSM/G) provides aircraft electrical power in case of emergency. On the green & yellow systems, the normal source of pressure is the Engine Driven Pump (EDP) and the auxiliary source is the PTU. The PTU is a hydraulic motor pump that transfers hydraulic power between the green and yellow systems without transfer of fluid. It operates automatically, whenever the pressure differential between the two systems reaches 500 PSI.
No Problem With Engines
The barking dog sound can be concerning for some passengers who may believe that an engine is cutting out. However, this noise has nothing to do with any problems with the engines. The PTU is only operational when the hydraulic pressure of the A320 or A330 drops below a pre-defined level. Due to pressure fluctuations, the noise will sometimes continue even after both engines are fully operational.
Interestingly, some Boeing aircraft also feature a PTU unit, but it doesn’t operate in the same way as the one employed on Airbus aircraft. The PTU has less involvement in Boeing’s aircraft and only intervenes when the aircraft is in the air.
Indeed, the barking dog sound on an Airbus A320 is not a cause for concern. Instead, it is a product of a valuable system that ensures pilots have access to all controls at all times. It can be annoying for some passengers, but understanding why it happens can help alleviate any concerns during your flight.
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
