What cabin differential should be observed prior to landing?

• A. Approximately 0 PSID
• B. Approximately 0.7 PSID
• C. Approximately 6.0 PSID
• D. Approximately -0.25 PSID

Answer: (B)

Cabin differential pressure is the difference between the pressure inside the cabin and the outside air. As you descend toward the field, the pressurization system slowly vents to ambient, so the cabin is gradually brought toward outside pressure but doesn’t snap all the way to equal outside pressure right before landing. In normal operation you’ll typically see a small positive differential, around 0.7 psi, just before touchdown. This small amount keeps the cabin slightly pressurized for a smooth, controlled release and helps maintain door seals and airflow behavior when you go to the gate. Values near zero would indicate full equalization with outside pressure, which isn’t how the system is usually left during approach. A much larger differential would exceed the system’s limits, and a negative differential would mean the outside is higher than inside, which isn’t normal during approach.