Originally Posted by dream747
......does the PFD on our modern jets today display IAS, CAS or EAS? ....... I understand that CAS is IAS corrected for position and instrument errors, and EAS is CAS corrected for compressibility error.
Your airspeed indicator displays IAS
by definition. The sensors don't sit in the pure freestream. The CAS is what they would display if they did. Modern kit corrects for the difference in the air data computation system before display, so often IAS=CAS.
EAS is not anything corrected for compressibility error. Say the dynamic pressure is Q_actual. EAS is the velocity your aircraft would have if it were to experience Q_actual at sea level.
PBL