What is the maximum positive cabin pressure differential?

• A. 8.0 PSI
• B. 9.0 PSI
• C. 8.7 PSI
• D. 7.5 PSI

Answer: (C)

The maximum positive cabin pressure differential is the largest difference the cabin pressure can have over the outside air without risking structural damage to the aircraft. This limit is set by the strength of the fuselage and pressurization system, since the cabin is maintained at a higher pressure than the outside at cruise.

For most transport-category airliners, the design limit is about 8.7 psi. That value is widely used in manuals and training because it represents the typical upper bound that the aircraft’s structure is certified to withstand through countless pressurization cycles. In practice, the cabin is kept at the equivalent of roughly 6,000–8,000 ft, while the outside air at cruise is around 3–4 psi, yielding a differential near 8 psi—near the 8.7 psi limit. In metric terms, that’s about 60 kPa.

So the best answer reflects the standard maximum differential for commonly used airframes.