Originally Posted by
galaxy flyer
As we climb, that EAS remains, but compressibility requires a higher INDICATED airspeed to Produce that EQUIVALENT airspeed over the wing.
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Calibrated airspeed (CAS) exists because it is best way you can calibrate a mechanical airspeed indicator. With modern electronic flight displays CAS is no longer necessary. It would be logical (and result in less variation in staling speed) to calibrate a PFD speed tape to read KEAS. This would be a simple matter of re writing some code in the air data computer. The reason most modern PFDs are calibrated to read KCAS is because of historical precedent and desire for commonality with mechanical airspeed indicators.
AFIK, the Eclipse business jet has its PFD speed tape calibrated to read KEAS.