Air pressure inside the cabin is lower than outside. What primarily causes this difference?

• A. Venturi effect
• B. Higher outside atmospheric pressure
• C. Increased cabin temperature
• D. Sealed cabin with equal pressure

Answer: (A)

Venturi effect is the reason a pressure difference is created and regulated here. When air is forced through a restricted outlet or duct, it speeds up as it passes the narrow section. According to this effect, the faster flow corresponds to a drop in static pressure in that constricted area. That lower pressure region inside the flow path helps control how much air leaves the cabin, establishing the difference between the cabin’s pressure and the outside air. The other factors listed don’t account for this primary mechanism—the restricted flow causing a pressure drop is what sets and maintains the differential.