Definition
A category covering the four distinct airspeed values pilots work with: Indicated Airspeed (IAS), Calibrated Airspeed (CAS), Equivalent Airspeed (EAS), and True Airspeed (TAS). Each represents the aircraft's speed through the air measured or corrected in a different way, accounting for instrument error, position error, air compressibility, and air density.
Plain English
Airspeed isn't just one number. There are four different versions of it, each calculated a little differently. Some are read straight off the instrument, others are corrected for errors or for the thinness of the air at altitude. Pilots use the right one depending on what they're trying to figure out.
Context Anchor
Seen in instrument flying, airspeed indicator discussions, performance calculations, wind correction, and flight planning.
Why Pilots Care
Correct use of each type prevents over- or under-estimating aircraft performance, ensuring proper speeds for takeoff, cruise, approach, and landing.
Grounding Statement
The same flight can show one speed on the cockpit instrument while the airplane is moving through the air, and across the ground, at different speeds.
Intuition Check
Do not assume every speed number means the same thing. Airspeed is about motion relative to the air; groundspeed is about motion over the earth.
Example Sentence 1
The instructor explained the four types of airspeed before showing how each one is used in flight planning.
Example Sentence 2
During preflight planning the student converted between types of airspeed to confirm the approach speed was safe.