Which instrument(s) will become inoperative if the static vents become clogged?

• A. Airspeed, altimeter, and vertical speed
• B. Airspeed only
• C. Altimeter only
• D. Turn coordinators

Answer: (A)

Static pressure is the reference that several instruments rely on to read their values. When the static vents become clogged, that reference is lost for those instruments.

The altimeter depends on ambient static pressure to show your altitude; with the static source blocked, it can freeze at the current reading or display an incorrect altitude. The vertical speed indicator measures your rate of climb or descent by detecting changes in static pressure; with no usable static input, it cannot register proper vertical movement and may freeze or misread. The airspeed indicator uses the difference between pitot (dynamic) pressure and static pressure to show airspeed; if the static path is blocked, the instrument loses its reference and will become unreliable or stop responding correctly.

The turn coordinator is powered by its own gyro system (vacuum or electric) and does not rely on the static pressure input, so it remains operational.