What is HYD on Boeing 737? (Hydraulic)

The Boeing 737 is undoubtedly one of the most widely-used commercial aircraft in the world. With its exceptional performance and reliability, it has become a staple in the aviation industry. One crucial component that contributes to the aircraft’s functionality is its hydraulic system. The hydraulic system, abbreviated as HYD, plays a critical role in the operation of various aircraft systems in the Boeing 737. In this article, we will delve into the details of the hydraulic system on the Boeing 737 and explore its significance in ensuring a safe and efficient flight.

The Importance of Hydraulic System on Boeing 737

The hydraulic system on the Boeing 737 is responsible for powering essential flight control systems, landing gear operation, and various other critical functionalities. It utilizes hydraulic fluid under pressure to transmit force or energy to perform work. This system is vital for several reasons:

1. Flight Controls

Hydraulic power is crucial for the operation of the flight control systems on the Boeing 737. The mechanical input from pilots manipulating the control surfaces, such as the ailerons, elevators, and rudder, is translated into hydraulic power to move the control surfaces. This allows the pilots to command the aircraft’s movements with precision and responsiveness. Without the hydraulic system, controlling the aircraft’s flight would be extremely challenging, if not impossible.

The hydraulic system works in conjunction with other aircraft systems, such as the autopilot, to provide a smooth and stable flight experience. It ensures that the control surfaces respond quickly and accurately to pilot input, thereby enhancing the overall maneuverability and control of the aircraft.

2. Landing Gear Operation

The landing gear system on the Boeing 737 is another critical component that relies on hydraulic power. The hydraulic system provides the force required to extend and retract the landing gear during takeoff and landing. It ensures that the landing gear operates smoothly and reliably, enabling safe and controlled landings.

The hydraulic system also enables the landing gear to be locked securely in place during flight to prevent any unwanted movement. This ensures stability and minimizes the risk of gear collapse or failure during turbulent situations or hard landings. The reliability of the hydraulic system is vital in guaranteeing the aircraft’s safe landing and passenger safety.

3. Braking and Anti-Skid System

The braking system in the Boeing 737 depends on hydraulic power to bring the aircraft to a safe stop on the runway. Hydraulic pressure is applied to the wheel brakes to generate friction and slow down the aircraft during landing or aborted takeoffs. The anti-skid system, which prevents the wheels from locking up and potentially causing a skid, is also controlled by hydraulic pressure.

This system allows the pilots to have precise control over the braking action, ensuring that the aircraft comes to a stop within the desired distance. The hydraulic system’s reliability is essential in providing consistent braking performance, especially during emergency situations or adverse weather conditions.

The Hydraulic System Components

The hydraulic system on the Boeing 737 consists of several components that work together to ensure its proper functioning. These components include:

1. Hydraulic Pumps

The hydraulic pumps are responsible for generating the necessary pressure to drive the hydraulic system. There are three hydraulic pumps in the Boeing 737: two engine-driven pumps and one electric motor-driven pump. The engine-driven pumps utilize engine power to pressurize the hydraulic fluid, while the electric motor-driven pump serves as a backup in case of engine failure.

The hydraulic pumps provide power to various hydraulic systems, including the flight controls, landing gear, and brakes. They play a crucial role in maintaining the hydraulic pressure required for reliable operation.

2. Reservoir and Accumulators

The hydraulic reservoir is responsible for storing the hydraulic fluid used by the system. It ensures a constant supply of fluid and acts as a heat sink to dissipate heat generated during operation. The reservoir also helps eliminate air bubbles or contaminants from the hydraulic fluid, ensuring its cleanliness and proper functioning.

Accumulators, on the other hand, store hydraulic energy under pressure and provide an additional source of power during peak demand situations. They contribute to system efficiency and enhance the responsiveness of the hydraulic system.

3. Actuators and Control Valves

The actuators and control valves are crucial components that convert hydraulic power into mechanical motion and control the flow of hydraulic fluid, respectively.

The actuators use hydraulic pressure to move the aircraft’s flight control surfaces, landing gear, and brakes. These include hydraulic cylinders, which translate the hydraulic force into linear motion, and hydraulic motors, which convert the hydraulic energy into rotary motion.

The control valves, on the other hand, regulate the flow and pressure of the hydraulic fluid throughout the system. They ensure that the hydraulic power is distributed appropriately and that the different aircraft systems receive the required amount of hydraulic force for optimal operation.


The hydraulic system on the Boeing 737 is indisputably vital for the aircraft’s safe and efficient operation. From controlling the flight surfaces to managing the landing gear and brakes, the hydraulic system ensures the pilot’s ability to maneuver and control the aircraft with precision. Understanding the significance of the hydraulic system and its components is crucial for aviation professionals and enthusiasts alike as they delve into the complexities of this remarkable aircraft. With its robust hydraulic system, the Boeing 737 continues to soar through the skies, providing reliable and comfortable flights for millions of passengers around the world.

For more information about Boeing 737 aircraft, you can visit Boeing’s official website.

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