To be a safe pilot, you will need to have a thorough understanding of airspeed and the different types of airspeed as flying is not the same as driving a car. Hence, a recent article in the September/October issue of FAA Safety Briefing by FAA Flight Test Engineer Jason Brys is well worth reading because he covers the topics of groundspeed, true airspeed, indicated airspeed (IAS) and calibrated airspeed (CAS) plus the need to understand the published airspeeds (indicated or calibrated) for whatever aircraft you are flying. Jason began his article by covering each type of airspeed in-dept:
Groundspeed. Jason pointed out that pilots need to understand that the speed shown on the aircraft’s indicator may not be the actually speed of the aircraft as other factors like wind could be influencing the aircraft’s “true speed.”
True Airspeed. Jason also noted that true speed, which is a measure of the speed of the aircraft in relation to the airflow around it, can also vary during different types of air density conditions that occur at different altitudes.
Indicated Airspeed (IAS). Jason wrote that indicated airspeed matters significantly as it indicates the bounds of the airspeed that an aircraft can operate in.
Calibrated Airspeed (CAS). Jason also explained that calibrated airspeed (CAS) accounts for any system or so-called position errors that an aircraft experiences as calculating an aircraft’s speed is obviously more complicated than establishing the speed of an automobile.
Why does all of this matter? As Jason pointed out, the differences between IAS and CAS may vary or increase depending upon certain factors and the type of aircraft you are flying. In other words and to use an example Jason used, if your airspeed indicator shows a stall speed at an IAS of 50 knots, your aircraft may in fact stall at an CAS of 58 knots.
At the end of his article, Jason concluded by writing that if you fly at the right airspeed, you will also be flying within the approved safety margin for an aircraft and hence, you will be a much safer pilot – a point well worth noting.
Ground speed technically is not an airspeed since it is your velocity relative to the ground rather than the air. Equivalent airspeed is another that could be added here!