What happens to the airspeed indicator when the static pressure line is disconnected?

When the static pressure line is disconnected, the airspeed indicator experiences a change in how it reads airspeed due to the loss of reference to the ambient static pressure outside the aircraft. The airspeed indicator relies on both dynamic pressure (from the pitot tube, which measures the pressure of the moving air) and static pressure (measured from the static source) to provide an accurate reading of the aircraft's speed relative to the air.

With the static pressure line disconnected, the airspeed indicator loses the ability to reference the ambient static pressure correctly. This results in an inaccurate reading, causing the device to interpret lower dynamic pressures in comparison to the static pressure it would normally reference. Consequently, the airspeed indication becomes lower than the actual speed of the aircraft through the air, leading to the indicator reading low. It is essential for flight engineers and pilots to understand this relationship, as it has implications for safety and performance during flight.