Open pilots/copilots sliding window and check differential pressure gauge above crew entry door to ensure differential pressure is _____.

• A. zero
• B. one
• C. two
• D. three

Answer: (A)

Opening the cockpit sliding window is only safe when there’s no pressure difference between the inside and outside. The differential pressure gauge above the crew entry door measures that difference. When you see zero, it means the cabin (inside) and outside air are at the same pressure, so opening the window won’t drive a strong rush of air or stress the window frame. Any nonzero reading means there’s a pressure difference that could cause a dangerous rush of air, door or window movement, or injury. So the correct condition to open the window is a zero differential pressure.