The airplane must be completely depressurized prior to which action?

• A. Opening any of the airplane doors.
• B. Starting engines
• C. Taxiing with wheels up
• D. Engaging the autopilot

Answer: (A)

Opening any door requires the cabin to be at roughly the same pressure as the outside air. When the airplane is pressurized in flight, there is a large differential pressing on the door from inside to outside, and a plug-type door is designed to resist that force, making it effectively impossible or extremely dangerous to open. Depressurizing the cabin to ambient outside pressure removes that differential, allowing the door to be opened safely. The other actions—starting engines, taxiing with wheels down, and engaging the autopilot—do not require depressurization, so they are not tied to this condition.