When the pitot tube and pitot tube drain port become blocked, what happens to the airspeed reading?

When the pitot tube and the drain port become blocked, the airspeed reading responds differently than one might intuitively expect. The pitot system works by measuring dynamic pressure from the airflow, but if both the pitot tube and its drain port are blocked, the input to the airspeed indicator becomes static.

In level flight, where the altitude is stable and the aircraft is not changing speed, the blocked system will maintain a constant reading because the pressure does not change significantly. Additionally, during power changes, the airflow may momentarily alter, but the airspeed indicator will not reflect these changes as it relies on the static pressure from the blocked pitot system, meaning the reading will appear unchanged.

This characteristic of maintaining a constant airspeed reading, despite the fact that the aircraft may be losing or gaining speed due to the effects of power changes and changing atmospheric conditions, is crucial for pilots’ understanding of how their instruments behave under abnormal conditions. Therefore, the proper choice reflects that, in level flight, the airspeed reading remains constant despite changes in power due to the characteristics of the blocked pitot tube system.