What is the relationship between IAS and CAS?

The relationship between Indicated Airspeed (IAS) and Calibrated Airspeed (CAS) revolves around the concept of airspeed measurement corrections. Indicated Airspeed is the reading from the aircraft's airspeed indicator, which does not account for certain errors that can distort the true airspeed data. These errors stem from both instrument inaccuracies and positional errors, primarily due to the specific location of the pitot tube and static ports on the aircraft.

Calibrated Airspeed, on the other hand, is the speed that the pilot should be concerned with when flying. It adjusts the Indicated Airspeed to correct for these errors, taking into account factors such as instrument error and position error. By utilizing CAS, pilots receive a more accurate representation of their true airspeed performance, which is critical for flight operations, particularly during phases of flight where speed management is essential, such as takeoff and landing.

In summary, the correct answer highlights that IAS is indeed impacted by errors, and CAS serves to correct those errors, providing a more accurate indication of airspeed for safe and effective navigation and performance.