Home Boeing Boeing 737 What is OFL on Boeing 737? (Outflow)

What is OFL on Boeing 737? (Outflow)

The outflow valve, commonly referred to as OFL on the Boeing 737 aircraft, is a crucial component of the aircraft’s environmental control system (ECS). This valve controls the flow of air from the cabin to the outside atmosphere, ensuring a safe and comfortable environment for passengers and crew onboard. In this article, we will delve deeper into the functionality and importance of the outflow valve, exploring its role in maintaining cabin pressure and regulating temperature during flight.

Ensuring Cabin Pressurization

Cabin pressurization is a critical factor in aviation, as it allows passengers and crew to breathe comfortably at high altitudes where the air is substantially thinner. The outflow valve plays a vital role in maintaining the desired cabin pressure throughout the flight.

When the aircraft is preparing for takeoff, the outflow valve is initially closed. As the engines power up and the aircraft gains altitude, the cabin altitude increases as well. To prevent excessive pressurization and ensure equalization, the outflow valve gradually opens to allow a controlled outflow of air. This process is necessary to maintain a comfortable and safe cabin environment.

The outflow valve continuously monitors the pressure difference between the inside and outside of the cabin. This pressure differential is measured by the cabin pressure controller, which then sends signals to the valve to adjust its position accordingly. By regulating the outflow of air, the valve helps maintain a consistent and safe cabin pressure, preventing discomfort and potential health risks to passengers and crew.

Regulating Temperature

In addition to its role in cabin pressurization, the outflow valve also plays a crucial role in regulating temperature inside the aircraft. As the aircraft climbs to higher altitudes, the outside air temperature gradually decreases. The cabin temperature, however, needs to be maintained at a comfortable level for the occupants.

The outflow valve allows the cabin air temperature to be controlled by regulating the flow of fresh air from the aircraft’s air conditioning system. The valve’s position determines the rate at which the warm or cool air is expelled from the cabin, ensuring that the desired temperature is maintained throughout the flight.

Furthermore, the outflow valve works in conjunction with other components of the aircraft’s ECS, such as the air conditioning packs, to maintain a balanced temperature distribution. As the packs cool or heat the fresh air entering the cabin, the outflow valve ensures that the temperature inside remains steady and comfortable for all occupants.

Maintaining Safety and Efficiency

The outflow valve not only contributes to the comfort of passengers and crew but also plays a crucial role in ensuring the safety and efficiency of the aircraft.

By maintaining a controlled cabin pressure, the outflow valve helps reduce the stress on the aircraft’s structure, ensuring its integrity and longevity. Additionally, it allows the aircraft to operate at higher altitudes, where fuel efficiency is improved due to lower air resistance and better aerodynamic performance.

Moreover, the outflow valve is equipped with fail-safe mechanisms to ensure the safety of the cabin environment. If the pressure differential exceeds safe limits or if the valve malfunctions, the cabin pressure controller will automatically close the valve and activate the necessary safety protocols.

It is worth mentioning that the outflow valve system on the Boeing 737 aircraft is continuously monitored by the flight crew and the aircraft’s systems. Any irregularities or malfunctions are promptly identified and rectified to maintain the highest level of safety and reliability.


The outflow valve, abbreviated as OFL on the Boeing 737 aircraft, is a critical component of the aircraft’s environmental control system. It ensures proper cabin pressurization, regulates temperature, and contributes to the overall safety and efficiency of the aircraft. By understanding the role and functionality of the outflow valve, we can appreciate the complex systems at work that allow for a comfortable and secure flying experience for all.

For More: What is ESDS on Boeing 737? (Electrostatic Discharge Sensitive)

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