What is EMP on Boeing 737? (Electric Motor Pump)

The Electric Motor Pump (EMP) or ACMP (Auxiliary Control Motor Pump) is a crucial component of the Boeing 737 aircraft’s hydraulic system. It plays a vital role in providing hydraulic power for various functions, ensuring the safe and efficient operation of the aircraft. In this article, we will delve into the details of the Electric Motor Pump (ACMP) and understand its importance in the functioning of the Boeing 737.

Understanding the Electric Motor Pump (ACMP)

The Electric Motor Pump (ACMP) is responsible for generating hydraulic pressure and supplying it to different systems within the Boeing 737. It consists of an electric motor coupled with a hydraulic pump, which makes it a compact and efficient component. The ACMP operates at a nominal voltage of 28 volts and can deliver hydraulic pressure up to 3000 psi (pounds per square inch).

The ACMP has redundant power sources, ensuring that even if one power source fails, the other takes over seamlessly. This redundancy provides an added layer of safety, preventing the loss of hydraulic power in critical situations. For instance, in the event of an engine failure, the ACMP can still provide hydraulic power to control essential flight surfaces, such as the ailerons, elevators, and rudder.

The ACMP is an integral part of the primary hydraulic system on the Boeing 737. It is used to power the flight controls, landing gear, and other hydraulic-dependent systems. The hydraulic pressure generated by the ACMP is distributed through numerous hydraulic lines, ensuring that each system receives the necessary power for its operation.

The Role of the Electric Motor Pump (ACMP) in the Hydraulic System

The Electric Motor Pump (ACMP) is primarily responsible for supplying hydraulic pressure to the various subsystems of the aircraft. Let’s take a closer look at its role in the hydraulic system of the Boeing 737:

1. Powering the Flight Controls

The flight controls of the Boeing 737, including the ailerons, elevators, and rudder, rely on hydraulic power for their operation. The ACMP ensures a continuous supply of hydraulic pressure to these flight control surfaces, enabling precise and responsive control of the aircraft during various phases of flight. In the event of engine failure or loss of hydraulic power from other sources, the ACMP acts as a backup, ensuring that the pilot maintains control over the aircraft.

It is important to note that the ACMP is not the sole provider of hydraulic power for the flight controls. The Boeing 737 also employs other hydraulic systems, such as the Engine Driven Pump (EDP), to ensure redundancy and prevent a complete loss of control in case of system failures.

2. Operating the Landing Gear

The landing gear of the Boeing 737 is another critical system that relies on hydraulic power. The ACMP supplies hydraulic pressure to activate the landing gear’s extension and retraction, as well as its locking mechanism. Without the ACMP, the landing gear would remain inoperable, leading to unsafe takeoffs and landings.

In addition to the ACMP, the Boeing 737 utilizes dedicated hydraulic pumps exclusively for the landing gear system, providing redundancy and increasing the overall reliability of the system.

3. Supporting Other Hydraulic-Dependent Systems

Aside from the primary functions mentioned above, the Electric Motor Pump (ACMP) also supports other hydraulic-dependent systems on the Boeing 737. These include:

– Spoilers: The ACMP provides hydraulic power to deploy and retract the spoilers, which assist in reducing lift and increasing drag during landing and certain flight phases.

– Thrust Reversers: The ACMP supplies hydraulic pressure to engage the thrust reversers, enhancing the deceleration of the aircraft during landing rollouts and improving safety.

– Brakes: Hydraulic pressure generated by the ACMP enables the activation of the aircraft’s brakes, allowing for effective deceleration on the runway.

It is worth mentioning that the Boeing 737 employs a redundant hydraulic system, incorporating multiple hydraulic pumps, reservoirs, and distribution lines. This redundancy ensures continuous operation even in the event of a single component failure, improving the overall safety and reliability of the aircraft.


The Electric Motor Pump (ACMP) on the Boeing 737 is a critical component of the aircraft’s hydraulic system. It plays a vital role in providing hydraulic power to various systems, including the flight controls, landing gear, spoilers, thrust reversers, and brakes. The ACMP ensures redundancy and backup power sources, enhancing the safety and reliability of the aircraft in critical situations.

Understanding the Electric Motor Pump (ACMP) and its functions in the Boeing 737 allows for a deeper appreciation of the complexities and robustness of modern aircraft systems. The continuous advancements in aviation technology continue to enhance the safety and efficiency of air travel, ensuring passengers can fly with confidence.

For More: What is OVDR on Boeing 737? (Overdoor)