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TAS can be obtained from the following data:
  • A
    EAS and air density.
  • B
    CAS and pressure altitude.
  • C
    EAS and pressure altitude.
  • D
    CAS and air density.
Dynamic pressure varies with the airspeed and the density of the air. Since the ASI is calibrated with the ISA air density, it will give erroneous indications anytime the air density is different from the standard ISA density. This is called the density error. Density decreases with altitude and the IAS, and thus the EAS will become gradually lower than the TAS. To calculate the appropriate correction, you can use the following formula:

EAS = TAS x √ (ρ ÷ ρO)

Where:
ρ: density of the air at the aircraft’s altitude.
ρO: density of the air at MSL.
 

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