What is EPRL on Boeing 737? (Engine Pressure Ratio Limit)

The Engine Pressure Ratio Limit (EPRL) is a critical parameter in the operation of the Boeing 737 aircraft. It refers to the maximum pressure ratio that the aircraft’s engines can achieve during flight. The EPRL plays a vital role in determining the performance and efficiency of the engines, as well as ensuring their safe operation within prescribed limits.

To understand the EPRL in more detail, let’s explore its significance and the factors that influence it.

Importance of Engine Pressure Ratio Limit

The EPRL is a key parameter that affects the overall efficiency of the aircraft’s engines. It determines the compression ratio of the engine, which directly impacts its power output, fuel consumption, and environmental emissions. By maintaining the EPRL within safe limits, the engines can operate optimally, delivering the required thrust while minimizing fuel consumption and emissions.

The EPRL also plays a crucial role in ensuring the safety of the aircraft. Operating an engine beyond its pressure ratio limit can result in compressor stall, which can lead to a loss of power and potential engine damage. By adhering to the EPRL, pilots and maintenance crews can minimize the risk of such incidents, promoting the overall reliability and safety of the aircraft.

Boeing, the manufacturer of the 737 aircraft, sets specific EPRL limits for each engine model used on the aircraft. These limits are based on extensive testing and analysis to determine the optimal operating range for the engines. Adhering to these limits is essential for maintaining the longevity and reliability of the engines throughout their service life.

Factors Influencing the Engine Pressure Ratio Limit

Several factors influence the EPRL of the aircraft’s engines. Understanding these factors can help pilots and maintenance personnel make informed decisions regarding engine operation and maintenance:

1. Engine Design and Performance

The design and performance characteristics of the engine heavily influence the EPRL. Modern engines, such as the CFM56 or the LEAP-1B, feature advanced high-pressure compressors that can achieve higher pressure ratios compared to older engine designs. These newer engines often have higher EPRL limits, allowing for improved overall performance and efficiency.

In addition to the engine design, the performance of the engine’s components, such as the compressor and turbine, also impact the EPRL. Higher-performing components can handle higher pressure ratios, resulting in increased EPRL limits.

2. Environmental Conditions

The environmental conditions in which the aircraft operates also affect the EPRL. Higher altitudes, lower ambient temperatures, and lower air densities can all influence the pressure ratio limits. At higher altitudes, the air becomes thinner, reducing the compressibility and affecting the efficiency of the engine. Therefore, the EPRL limits may be lower at higher altitudes to prevent engine performance degradation and potential damage.

In extreme weather conditions, such as high temperatures or very cold environments, the EPRL limits may also be adjusted to account for these variations. This ensures that the engine can operate within safe parameters and maintain its performance and reliability.

3. Engine Maintenance and Degradation

The maintenance and degradation of an engine can impact its EPRL. Over time, components may experience wear and tear, potentially affecting their ability to handle higher pressures. Regular maintenance and inspections are critical to ensure that the engine remains within its EPRL limits and to identify any potential issues or degradation that could lead to unsafe operating conditions.

Additionally, operators must closely monitor the engine’s health and performance through regular engine trend monitoring and analysis. This allows for identifying any deviations from normal operating parameters or signs of degradation that could affect the EPRL.


The Engine Pressure Ratio Limit (EPRL) on the Boeing 737 is a crucial parameter that impacts the efficiency, performance, and safety of the aircraft’s engines. By maintaining the EPRL within safe limits, pilots and maintenance personnel can ensure optimal engine operation, minimize fuel consumption and emissions, and enhance the overall reliability of the aircraft.

Understanding the factors that influence the EPRL, such as engine design, environmental conditions, and maintenance, is key to effectively managing and monitoring the engine’s performance. By considering these factors and adhering to the manufacturer’s specified EPRL limits, operators can maximize the lifespan and efficiency of the engines while promoting safe and reliable operations.

For More: What is CMM on Boeing 737? (Component Maintenance Manual)