If the instrument static pressure line becomes disconnected inside a pressurized cabin during cruising flight, the altimeter will read

If the instrument static pressure line becomes disconnected inside a pressurized cabin during cruising flight, the altimeter will read

• A. Read high
• B. Read low
• C. Read normal but unstable
• D. No change

Answer: (B)

The altimeter uses static pressure to determine altitude, with higher pressure indicating lower altitude and lower pressure indicating higher altitude. In a pressurized cabin, the static pressure inside is kept higher than the outside air pressure at cruising altitude. If the static line becomes disconnected from the outside and instead connects to cabin air, the altimeter will receive this higher cabin pressure. Because it’s fed with more pressure than the true outside air, the instrument will interpret that as being at a lower altitude than you actually are. At cruising, where outside pressure is low and cabin pressure remains relatively high, this causes a downward indication, so it will read low.

The altimeter uses static pressure to determine altitude, with higher pressure indicating lower altitude and lower pressure indicating higher altitude. In a pressurized cabin, the static pressure inside is kept higher than the outside air pressure at cruising altitude. If the static line becomes disconnected from the outside and instead connects to cabin air, the altimeter will receive this higher cabin pressure. Because it’s fed with more pressure than the true outside air, the instrument will interpret that as being at a lower altitude than you actually are. At cruising, where outside pressure is low and cabin pressure remains relatively high, this causes a downward indication, so it will read low.