Airspeed Indicator (ASI)

The Airspeed Indicator (ASI) is a primary flight instrument that measures the pressure difference between pitot (dynamic) and static air to determine the aircraft's indicated airspeed. A blockage of the pitot tube or static port will cause the ASI to provide inaccurate or misleading readings. Understanding the effect of each blockage type is essential for safe flight operations.

Key Points

• •Relies on both pitot (dynamic) pressure and static pressure sources to calculate indicated airspeed.
• •A blocked pitot tube (with the static port open) causes the ASI to <strong>overread in a climb</strong> and <strong>underread in a descent</strong>.
• •A blocked static port will negatively affect the ASI, VSI, and altimeter simultaneously.
• •This is frequently tested in the CASA exam — know the specific effect of each blockage type on each instrument.

Related Terms