Introduction

Hydraulic systems are vital to modern aviation, providing the power needed for essential aircraft operations such as landing gear, flight control surfaces, and braking systems. The Boeing 737, one of the most successful commercial aircraft, relies heavily on a well-engineered hydraulic system for its reliable and efficient operations. In this post, we will explore the hydraulic system used in the Boeing 737, as well as the history and reasons why hydraulic power is a cornerstone of aviation technology.

The History of Hydraulic Systems in Aviation

The concept of using hydraulics in aircraft goes back to the early 20th century when pilots sought ways to reduce manual effort in controlling larger aircraft. Before hydraulics, aircraft relied on cable and pulley systems that were heavy and required considerable force from pilots. As aircraft became larger and faster, hydraulic systems were developed to provide greater control authority with reduced pilot workload.

By the 1930s, hydraulic systems were integrated into military aircraft, providing power to retract landing gear and operate control surfaces. During World War II, hydraulic systems proved crucial to the success of bombers and fighters, allowing for more precise and reliable control. The technology continued to evolve in the subsequent decades, becoming an integral part of commercial aviation. The Boeing 737 is a prime example of how hydraulic technology has been harnessed to enhance flight safety and efficiency.

Why Use Hydraulic Systems?

Hydraulic systems are used in aviation because they provide high power density—meaning a relatively small volume of hydraulic fluid can generate a significant amount of power. This makes hydraulics ideal for aircraft, where weight is a critical factor. Hydraulics also provide smooth, consistent, and precise control, which is vital for flight-critical operations.

Moreover, hydraulic systems are reliable and can be designed with multiple redundancy features to enhance safety. For example, the Boeing 737 has a three-system hydraulic layout that ensures continuous operation even if one system fails. These characteristics make hydraulic systems the preferred solution for powering key aircraft functions such as landing gear extension/retraction, flight controls, spoilers, and brakes.

The Boeing 737 Hydraulic System

The Boeing 737 features a robust hydraulic system that ensures the proper functioning of various flight-critical components. The hydraulic system consists of three main systems—A, B, and standby—each with specific functions but capable of backing each other up in case of a failure. Here’s a detailed look at each system:

1. System A
   • Primary Functions: System A powers essential components such as the primary flight controls (ailerons, elevators, and rudder), the landing gear, and the inboard flight spoilers.
   • Source: System A is powered by an engine-driven pump, which takes power from one of the aircraft’s engines. This ensures that as long as the engine is running, there is hydraulic power available.
2. System B
   • Primary Functions: System B powers other crucial components such as the secondary flight controls, including flaps and slats, as well as the outboard flight spoilers and alternate landing gear extension.
   • Source: Similar to System A, System B uses an engine-driven pump. However, it is also supplemented by an electric motor-driven pump, providing additional redundancy.
3. Standby System
   • Purpose: The standby system serves as an emergency backup in case both A and B systems fail. It powers key components like the rudder, thrust reversers, and leading-edge devices.
   • Operation: The standby system is automatically or manually activated, providing hydraulic power to ensure the safety of the aircraft during critical moments, such as landing.

Key Components of the Boeing 737 Hydraulic System

• Hydraulic Pumps: The Boeing 737 hydraulic system includes engine-driven pumps and electric motor-driven pumps. These pumps generate hydraulic pressure, ensuring that sufficient power is available for all operations. The redundancy provided by using both engine-driven and electric pumps enhances reliability.
• Reservoirs and Accumulators: Each hydraulic system has a reservoir that stores hydraulic fluid. The accumulators help maintain pressure within the system and provide a reserve of hydraulic power for emergency use.
• Filters and Valves: The hydraulic system contains filters to keep the fluid clean and check valves to prevent backflow, maintaining proper system functionality. Shutoff valves are also used to isolate certain parts of the system when maintenance is required.

How the Hydraulic System Works

Hydraulic power in the Boeing 737 is generated by pumps that convert mechanical energy (from the engines or electric motors) into hydraulic energy. This energy is used to pressurize the fluid within the system, which is then distributed to various actuators.

These actuators convert hydraulic pressure into mechanical force, which in turn moves flight control surfaces, retracts or extends landing gear, or applies the brakes. The entire system is controlled by hydraulic control panels in the cockpit, allowing pilots to monitor pressure levels and detect any faults.

Boeing 737 hydraulic system – Reliability Through Redundancy

One of the key features of the Boeing 737 hydraulic system is its redundancy. The three independent systems (A, B, and standby) ensure that even if one system becomes inoperative, the aircraft can still be safely operated using the remaining systems. This redundancy is crucial for maintaining control during all phases of flight, especially during takeoff and landing.

Did You Know?

• The use of hydraulic power in aviation dates back to the 1930s, but it wasn’t until the 1960s and 70s that sophisticated multi-redundant systems, like those found in the Boeing 737, became standard in commercial aviation.
• Hydraulic systems operate at very high pressures, typically around 3000 psi in the Boeing 737, providing the force needed to control heavy aircraft components with precision.
• Unlike many modern aircraft, which are adopting fly-by-wire technology, the Boeing 737 retains its hydraulic linkages, providing pilots with a more traditional and tactile flying experience.

Boeing 737 hydraulic system – Conclusion

The Boeing 737 hydraulic system is a testament to the importance of hydraulic power in aviation. It provides the force required for critical flight operations while ensuring redundancy and reliability. By harnessing the power of hydraulics, the Boeing 737 continues to be one of the most reliable and safe aircraft in commercial service today. The evolution of hydraulic technology has played a crucial role in making modern air travel possible, and the Boeing 737’s hydraulic system is an excellent example of this technology in action.