Which condition can cause the ASI to show zero airspeed?

Which condition can cause the ASI to show zero airspeed?

• A. RAM air inlet blocked but drain hole open
• B. Drain hole blocked but RAM air inlet open
• C. Both RAM air inlet and drain hole open
• D. Blocked alternate static source

Answer: (A)

The situation where the Airspeed Indicator (ASI) shows zero airspeed occurs when there is an obstruction in the RAM air inlet but the drain hole is still open. The ASI functions by measuring the difference between static pressure and dynamic pressure; the latter is derived from air entering through the RAM air inlet. If the RAM air inlet is blocked, the instrument cannot receive the dynamic pressure needed to measure airspeed correctly. However, with the drain hole open, any pressure buildup in the tubing would be released, preventing the ASI from indicating any positive airspeed. Essentially, the inability to obtain dynamic pressure due to a blockage leads the ASI to indicate zero airspeed since it relies on that flow for accurate readings. This scenario emphasizes the importance of understanding how each component of the ASI system interacts with airflow to ensure accurate speed readings, especially in the context of instrument flying.

The situation where the Airspeed Indicator (ASI) shows zero airspeed occurs when there is an obstruction in the RAM air inlet but the drain hole is still open. The ASI functions by measuring the difference between static pressure and dynamic pressure; the latter is derived from air entering through the RAM air inlet.

If the RAM air inlet is blocked, the instrument cannot receive the dynamic pressure needed to measure airspeed correctly. However, with the drain hole open, any pressure buildup in the tubing would be released, preventing the ASI from indicating any positive airspeed. Essentially, the inability to obtain dynamic pressure due to a blockage leads the ASI to indicate zero airspeed since it relies on that flow for accurate readings.

This scenario emphasizes the importance of understanding how each component of the ASI system interacts with airflow to ensure accurate speed readings, especially in the context of instrument flying.