Understanding the PTU on Airbus A320: The Power Transfer Unit Explained

PTU Airbus

In the aviation industry, the Airbus A320 family stands as a testament to innovation and reliability. Among the various sophisticated components that contribute to its operational efficiency is the Power Transfer Unit (PTU). Despite its small size, the PTU plays a pivotal role in the aircraft’s hydraulic system. In this comprehensive blog post, we will delve into what the PTU Airbus A320 entails, how it functions, its significance, and common misconceptions surrounding it.

What is a PTU Airbus?

The Power Transfer Unit (PTU) in the context of Airbus A320 is a hydraulic device designed to transfer hydraulic power from one system to another without the actual transfer of hydraulic fluid. The PTU interlinks two of the aircraft’s three hydraulic systems, ensuring they can support each other in maintaining hydraulic pressure and operational integrity.

Hydraulic Systems on the Airbus A320

To fully grasp the importance of the PTU Airbus A320, it’s essential to understand the aircraft’s hydraulic systems. The A320 is equipped with three independent hydraulic systems: Green, Blue, and Yellow. Each system powers various essential aircraft components, such as:

  • Flight Control Surfaces: Including ailerons, elevators, rudders, and spoilers.
  • Landing Gear: For extension and retraction.
  • Brakes: On the main landing gear.
  • Nose Wheel Steering: To maneuver the aircraft on the ground.
  • Thrust Reversers: Assisting in deceleration after landing.

The Green and Yellow systems, which the PTU interconnects, are primarily powered by engine-driven pumps. The Blue system, however, operates independently, powered by an electric motor-driven pump.

Functioning of the Power Transfer Unit Airbus A320

The PTU is essentially a bidirectional hydraulic motor/pump assembly that transfers hydraulic power between the Green and Yellow systems. It does not transfer hydraulic fluid but equalizes pressure between the systems. Here’s a detailed look at its operation:

  1. Pressure Differential Detection: The PTU activates when it detects a significant pressure differential (approximately 500 psi) between the Green and Yellow systems.
  2. Activation Process: Upon activation, the PTU transfers hydraulic power from the system with higher pressure to the one with lower pressure. This action equalizes the pressure without mixing the hydraulic fluids.
  3. Pressure Equalization: The main purpose of the PTU is to ensure both systems maintain adequate hydraulic pressure, which is crucial for the aircraft’s safe and efficient operation.

Importance of the PTU Airbus A320

The PTU Airbus A320 is crucial for several reasons:

  1. Redundancy and Safety: The PTU provides redundancy by allowing one hydraulic system to support the other in case of failure. This redundancy is essential for maintaining control over flight-critical systems.
  2. Operational Reliability: By ensuring hydraulic systems can back each other up, the PTU enhances the aircraft’s reliability, preventing potential delays or cancellations due to hydraulic failures.
  3. Efficiency: Although the PTU itself does not directly impact fuel efficiency, it supports overall aircraft efficiency by maintaining optimal hydraulic system performance, which in turn ensures smooth operation of various aircraft systems.

The Distinctive “Barking Dog” Sound

A unique characteristic of the PTU Airbus A320 is the distinctive noise it produces when activated, often described as a “barking dog” sound. This noise is particularly noticeable when the aircraft is on the ground, during hydraulic system tests, or during engine start-up procedures. While this sound can be alarming to passengers unfamiliar with it, it is a normal part of the PTU’s operation, indicating that the system is functioning correctly.

Detailed Components and Operation of the PTU

To gain a deeper understanding of the PTU Airbus A320, let’s explore its components and detailed operation:

  1. Hydraulic Motor-Pump Assembly: The core component is the hydraulic motor-pump unit, which allows bidirectional power transfer without fluid transfer. The motor side is driven by hydraulic pressure from one system, which drives the pump side to pressurize the other system.
  2. Control Valves: The PTU includes control valves that regulate its operation. These valves manage the activation and deactivation of the PTU based on the pressure differential between the Green and Yellow systems, ensuring it operates only when necessary.
  3. Sensors and Monitoring: Equipped with sensors, the PTU system continuously monitors hydraulic pressures, providing real-time data to the aircraft’s central monitoring systems. This ensures quick detection and resolution of any pressure discrepancies.

Scenarios of PTU Operation

The PTU Airbus A320 plays a critical role in various scenarios:

  1. Engine Failure: If an engine fails, the hydraulic system powered by that engine loses pressure. The PTU can transfer power from the other system, ensuring continued operation of critical components like flight controls and landing gear.
  2. Hydraulic Pump Failure: In case of a hydraulic pump failure, the PTU transfers power from the system with the operational pump to maintain hydraulic pressure in both systems.
  3. Ground Operations: During pre-flight checks or ground operations, the PTU helps test the hydraulic systems, ensuring they function correctly before takeoff.

Maintenance and Troubleshooting

Maintaining the PTU Airbus A320 involves regular inspections and tests to ensure its functionality. Key maintenance practices include:

  1. Regular Inspections: Routine checks for signs of wear, leaks, or other issues that could affect performance.
  2. Functional Testing: Periodic tests to ensure the PTU activates and operates correctly under simulated conditions where power transfer is necessary.
  3. Troubleshooting: Addressing issues promptly, such as problems with control valves, sensors, or the motor-pump assembly, to maintain the PTU’s reliability.

Common Questions and Misconceptions

Given its critical role and distinctive noise, the PTU Airbus A320 often raises questions and misconceptions. Let’s address some common ones:

  1. Is the PTU sound a sign of malfunction?
    • No, the “barking dog” sound is a normal part of the PTU’s operation, indicating it is functioning correctly.
  2. Does the PTU transfer hydraulic fluid between systems?
    • No, the PTU transfers hydraulic power, not fluid. It equalizes pressure without mixing the hydraulic fluids of the Green and Yellow systems.
  3. Can the PTU operate during flight?
    • Yes, the PTU can operate both during flight and on the ground. It activates whenever there is a significant pressure differential between the Green and Yellow systems.
  4. Is the PTU always active?
    • No, the PTU activates only when needed to equalize pressure between the Green and Yellow systems. It remains inactive when both systems are functioning normally.


The Power Transfer Unit (PTU) on the Airbus A320 is a vital component that ensures the aircraft’s hydraulic systems operate efficiently and reliably. By transferring hydraulic power between the Green and Yellow systems, the PTU maintains operational integrity, even in the face of system failures or pressure discrepancies. This redundancy and reliability enhance the overall safety and efficiency of the A320, making it a critical player in the aircraft’s performance.

Understanding the PTU Airbus A320 helps demystify its operation and the noises it produces, reassuring passengers and highlighting the sophistication of modern aviation technology. The next time you fly on an A320 and hear that distinctive “barking dog” sound, you can appreciate the PTU’s role in keeping your flight smooth and safe.

Scroll to Top