If the pitot tube and outside static vents become clogged, which instruments would be affected?

• A. The altimeter, airspeed indicator, and vertical speed indicator
• B. The attitude indicator and heading indicator
• C. The airspeed indicator only
• D. The compass and turn coordinator

Answer: (A)

The key idea is how the pitot-static system provides pressure data for specific instruments. The pitot tube feeds a dynamic pressure signal used by the airspeed indicator, while the outside static vents supply ambient static pressure used by the altimeter and the vertical speed indicator (and also contribute to the airspeed indicator’s reading in combination with pitot pressure).

If both the pitot tube and the outside static vents become clogged, these three instruments lose their pressure inputs and can no longer display correct information. The airspeed indicator relies on the difference between pitot (dynamic) pressure and static pressure; with both blocked, it can read zero or behave erratically. The altimeter uses static pressure to determine altitude, so blocking static pressure can freeze the reading or give an incorrect altitude. The vertical speed indicator measures how quickly static pressure is changing; with the static system blocked, it may show no vertical movement or an erroneous rate.

Other instruments like the attitude indicator and heading indicator use gyros, and the compass and turn coordinator rely on magnetic or gyro systems rather than pitot-static pressures, so they aren’t directly affected by a clogged pitot and static system.