What is HYD on Boeing 777? (Hydraulic)

The Boeing 777 is a marvel of modern aviation, incorporating advanced technologies and systems to ensure a safe and efficient flight. One vital component of this aircraft is the hydraulic system, commonly known as HYD. The hydraulic system plays a crucial role in controlling various functions of the aircraft, providing the necessary power to move and operate different mechanisms. In this article, we will delve into the details of the hydraulic system on the Boeing 777 and understand its significance in the overall functioning of the aircraft.

Understanding the Hydraulic System

The hydraulic system on the Boeing 777 is responsible for powering and operating essential aircraft functions such as flight control surfaces, landing gear, brakes, and various other systems. It utilizes fluid power to generate, control, and transmit the necessary force to perform these tasks effectively. The hydraulic fluid, which is typically a specialized type of oil, is pressurized and distributed through a network of hydraulic lines, valves, and actuators.

Let’s take a closer look at some key components of the hydraulic system on the Boeing 777:

Hydraulic Fluid

The hydraulic fluid used in the Boeing 777 is carefully selected to meet stringent requirements for viscosity, temperature range, and compatibility with system materials. It acts as a medium to transmit power as it passes through the hydraulic lines, valves, and actuators. The fluid’s viscosity ensures smooth and efficient flow, while its resistance to temperature extremes ensures reliable operation even in challenging environments.

It is worth noting that the hydraulic fluid used in aircraft hydraulic systems is typically fire-resistant to prevent ignition or spread of fire in case of leaks or accidents. This is a critical safety feature, as a fire in the hydraulic system could lead to catastrophic consequences.

Hydraulic fluids used in the aviation industry generally fall into two categories: ‘Type IV’ and ‘Type V’. Type IV fluids are phosphate ester-based and offer excellent fire resistance properties, making them suitable for high-performance applications like the Boeing 777. On the other hand, Type V fluids are more commonly used in commercial aircraft due to their lower cost and satisfactory fire resistance characteristics.

Hydraulic Pumps

The hydraulic system of the Boeing 777 relies on hydraulic pumps to pressurize the hydraulic fluid, providing the necessary force to operate various aircraft systems. The pumps draw hydraulic fluid from the reservoir and generate the required pressure to move control surfaces, actuate landing gear, and engage the brakes.

There are typically three types of hydraulic pumps used in the Boeing 777: engine-driven pumps, electric motor-driven pumps, and a ratemeter-driven electric auxiliary pump. The engine-driven pumps are considered the primary source of hydraulic power and are directly powered by the aircraft’s engines. In the event of an engine failure, the electric motor-driven pumps and the ratemeter-driven electric auxiliary pump ensure that hydraulic power is still available to critical flight control surfaces.

Hydraulic Manifold

The hydraulic manifold is a crucial component that distributes hydraulic fluid from the pumps to different systems and actuators throughout the aircraft. It acts as a central hub, regulating the flow of hydraulic fluid and ensuring precise control and manipulation of the various flight control surfaces, landing gear, and other hydraulic-powered systems.

The Boeing 777 incorporates redundant hydraulic manifolds to enhance safety and reliability. This means that even if one manifold fails, there is a backup system in place to ensure the hydraulic power distribution remains unaffected. Redundancy is a fundamental principle in aviation design, minimizing the chances of critical system failures and enabling safe operation even in the presence of faults.

Additionally, the hydraulic manifold incorporates various valves, filters, and sensors to regulate and monitor the hydraulic system’s performance. These components play a vital role in maintaining optimal hydraulic pressure, temperature, and overall system integrity.


The hydraulic system, abbreviated as HYD, is an integral part of the Boeing 777 aircraft, powering and controlling essential functions such as flight control surfaces, landing gear, and brakes. It utilizes hydraulic fluid, which is pressurized and distributed through pumps, manifolds, valves, and actuators, to generate the necessary force for these operations. The hydraulic system ensures smooth and reliable performance, contributing to the overall safety and efficiency of the Boeing 777.

Understanding the hydraulic system is essential for pilots, aircraft technicians, and aviation enthusiasts alike. It provides insights into the intricate mechanisms behind the operation of modern aircraft and highlights the importance of hydraulic power in maintaining control and safety during flight.

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