What is the maximum negative differential pressure (negative press) allowed?

What is the maximum negative differential pressure (negative press) allowed?

• A. -0.5 psi
• B. -1.0 psi
• C. 0.0 psi
• D. -0.2 psi

Answer: (A)

Differential pressure limits in the pressurization system govern how far the cabin can differ from the outside air. While the cabin is kept positively pressurized during flight, a small negative differential is allowed to accommodate valve behavior and transient conditions without overstressing the airframe. For the ERJ 175, the most negative differential permitted is -0.5 psi, meaning the cabin can be up to 0.5 psi lower than ambient pressure. Going beyond that could introduce excessive suction loads on the fuselage or compromise door and seal integrity. The other values either exceed the design limit (more negative than -0.5 psi), or do not represent the maximum negative differential (0.0 psi is not a negative differential, and -0.2 psi is a less negative value).

Differential pressure limits in the pressurization system govern how far the cabin can differ from the outside air. While the cabin is kept positively pressurized during flight, a small negative differential is allowed to accommodate valve behavior and transient conditions without overstressing the airframe. For the ERJ 175, the most negative differential permitted is -0.5 psi, meaning the cabin can be up to 0.5 psi lower than ambient pressure. Going beyond that could introduce excessive suction loads on the fuselage or compromise door and seal integrity. The other values either exceed the design limit (more negative than -0.5 psi), or do not represent the maximum negative differential (0.0 psi is not a negative differential, and -0.2 psi is a less negative value).