Private Pilot Private Exam

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

1. Airspeed, altimeter, and vertical speed

2. Heading indicator and vertical speed

3. Magnetic compass and airspeed indicator

4. Altimeter and gyro instruments

The correct answer is: Airspeed, altimeter, and vertical speed

The airspeed indicator, altimeter, and vertical speed indicator rely on static pressure to function properly. If the static vents become clogged, these instruments will receive inaccurate or no static pressure information. The airspeed indicator measures the difference between static pressure and dynamic pressure (the pressure from the airflow around the aircraft). If static pressure is disrupted, the indicated airspeed will be incorrect or unreadable. The altimeter, which measures altitude based on static pressure, will also fail to provide accurate altitude information; it may freeze at a given altitude or show unreliable readings. Similarly, the vertical speed indicator, which detects changes in static pressure to indicate climb or descent rates, will no longer function correctly, leading to untrustworthy information about the pilot’s vertical motion. In contrast, the heading indicator relies on the aircraft's gyroscopic instruments and isn’t affected by static pressure changes, while the magnetic compass is based on magnetic forces rather than atmospheric pressure. Thus, the correct choice identifies those instruments that definitively depend on an unobstructed static source.