What does Indicated Altitude show?

Indicated altitude refers to the altitude reading displayed by the altimeter, which is determined using the local atmospheric pressure. This reading is derived under the assumption of standard atmospheric conditions, typically defined by the International Standard Atmosphere (ISA). When the altimeter is set correctly to the local barometric pressure, the indicated altitude reflects the height above sea level that the aircraft is at, but it is calibrated based on standard conditions, which may not always match actual atmospheric conditions.

Understanding this concept is critical for pilots, as discrepancies can arise between indicated altitude and the actual altitude due to variations in temperature and pressure. This emphasizes the importance of properly setting the altimeter to ensure accurate altitude readings during flight operations, especially in controlled airspace where altitude precision is crucial for safety.