When does the red CABIN PRESSURE CAS appear?

• A. When the cabin differential exceeds 6.35 PSI or drops below -0.25 PSI
• B. When the cabin differential exceeds 6.0 PSID
• C. When the cabin altitude exceeds 12,000 feet
• D. When the cabin differential drops below -0.50 PSI

Answer: (A)

The red CABIN PRESSURE CAS shows whenever the cabin differential pressure is outside safe limits. The aircraft maintains a pressure inside by keeping a difference between inside and outside air, and exceeding those limits or going too negative could stress the airframe or jeopardize occupants, so the red alert is triggered.

On the NGX, the protective limits are about a positive differential of 6.35 psi and a negative differential of -0.25 psi. When the differential climbs above 6.35 psi or drops below -0.25 psi, the red cabin pressure warning lights up and a warning is sounded.

That’s why the correct threshold involves 6.35 psi and -0.25 psi. Other options reference different thresholds (such as a cabin altitude at a certain feet or a slightly different positive limit) that do not align with the actual protected limits.