An aircraft is flying at FL370 with CAS = 300 kt . OAT = ISA -4°C. The compressibility factor is 0.932.
Calculate the TAS.
CAS to TAS with your flight computer
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Set pressure altitude in the window opposite the OAT in Celsius.
- Without moving the computer’s scales, read TAS on the outer scale opposite to CAS.
If the aircraft is flying in excess of 300 kts, a larger uncorrected compressibility error rises.
Any conversion from CAS to TAS results in TAS higher than 300 kts a a correction has to be made using the compressibility factor or using the compressibility window in your flight computer.
ISA temp. FL370 = 15 - 2 x 37 = -59º C, as the min. ISA temp. is - 56,5º, OAT = -56,5º - 4º = -60,5º C
Read TAS 556 kts on the flight computer , and finally apply the compressibility factor, 556 x 0,932 = 518 kts.
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