Hi,
This is my understanding of compressibility......
It has to be taken into consideration when Either;
1) TAS > 300kts
2) CAS > 200Kts
3) Mach > 0.4m
The ASI is calibrated for standard ISA condidtions (hence why at sea level in ISA conditions if you fly at SLOW speed IAS/CAS = EAS = TAS).
The ASI gives you a reading of IAS/CAS - therefore you would not want to 'calibrate' out compressibility - as if you did you are then showing EAS, which is not what the purpose of the ASI is.
Hope this helps!
G-A-G
Last edited by Get-a-Grip; 30th October 2009 at 09:05.