Which statement about aircraft pressurization and door operation is correct?

• A. Doors are unaffected by cabin pressurization; all doors can be opened at any altitude.
• B. Aircraft are normally pressurized above 14,000 ft; plug-type doors cannot be opened while pressurized, and non-plug doors can injure personnel.
• C. Pressurization only occurs during flight; doors are never restricted when pressurized.
• D. All door types remain locked until the aircraft lands.

Answer: (B)

The key idea is how cabin pressure interacts with different door designs. When an aircraft is pressurized, a substantial differential pressure exists across every door. Plug-type doors are built to seal tightly and resist being forced open by that pressure; the inside air effectively pushes the door against its frame, so a plug-type door cannot be opened while the cabin is pressurized. It usually requires depressurizing the cabin or servicing door mechanisms in a non-flight condition to open safely. Non-plug doors don’t rely on the same pressure-induced seal, so attempting to open them while the cabin is pressurized can unleash a powerful wind blast and pose a real risk to anyone nearby, potentially causing injury. Since aircraft are normally pressurized during flight, door operation is restricted to safe conditions (depressurized or ground operations). The other statements conflict with how pressure affects door behavior, making them incorrect.