FAA Instrument Rating Written Practice Test 2025 - Free Instrument Rating Exam Practice Questions and Study Guide

When both the ram air input and the drain hole of the pitot system are blocked, the airspeed indicator will not function correctly. The airspeed indicator measures dynamic pressure, which is obtained from the difference between the static pressure and the pressure captured by the ram air input. If the ram air input is blocked, the pressure reading will be held at the static pressure level at the moment of the blockage.

In a climbing flight, the aircraft's altitude increases, leading to a decrease in the ambient atmospheric pressure. As the static pressure decreases, the dynamic pressure remains effectively constant because the ram air input is obstructed. Consequently, the airspeed indication on the instrument will appear to increase, suggesting a higher airspeed than is actually present. This phenomenon occurs because the indicated airspeed is calculated based on the pressure being compared, which in this case artificially inflates the airspeed reading as the altitude changes.

Understanding this principle is crucial for pilots, especially for those operating under instrument flight rules, as it highlights the potential for misreading airspeed information in the event of pitot system blockages.