1.11 Speeds

• Indicated Airspeed (IAS): The dynamic pressure of air against a vehicle, or indicated airspeed, is equal to VipV2, where p = density, and V = true airspeed. An airspeed indicator, calibrated to ISA, mean sea level conditions records the dynamic pressure as a speed. If, for example, the indicated reading were 200 kt, then it means that the dynamic pressure is the same as it would be at a true air speed of 200 kt at standard conditions at mean sea level. 

• Rectified Airspeed (RAS): The indicated airspeed, corrected for instrument and position errors (IE and PE). 

• Equivalent Airspeed (EAS): The rectified airspeed corrected for compressibility(C). It should be noted that compressibility is always a subtracted quantity. 

• True Airspeed (TAS): The equivalent airspeed corrected for density. 

• Calibrated Airspeed (CAS): Some airspeed indicators are corrected for mean sea level compressibility. Calibrated airspeed is the value of this reading, corrected for instrument and position errors 

• Mach Number (Mn): Mach number is the ratio of TAS to the local speed of sound (LSS).