What happens to the airspeed indication when a pitot tube is blocked and the drain hole is also blocked?

When a pitot tube is blocked and the drain hole is also blocked, the airspeed indication becomes unreliable. The pitot tube measures the dynamic pressure of the air as the aircraft moves, which is essential for providing an accurate airspeed reading. If the pitot tube is blocked, the air pressure inside the tube will remain static and will not reflect the changing dynamic pressures as the aircraft's speed changes.

With the drain hole also blocked, any moisture or condensation that accumulates within the tube cannot escape, leading to further inaccuracies. The system becomes a sealed unit with a fixed pressure, which means that any change in altitude or aircraft speed will not affect the indicated airspeed. Consequently, pilots cannot rely on the airspeed indicator for accurate information, which is critical for safe flight operations. This situation can lead to dangerous scenarios, especially if the pilot misreads the airspeed and miscalculates stall speed or required performance metrics.