Airspeed questions
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Join Date: May 2016
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Airspeed questions
Hi,
1. is the IAS on your PFD a CAS or EAS? When reading the FCOM's, I would say it is CAS; however, wouldn't it make more sense that this should be EAS, since EAS is IAS corrected for position AND compression error (and compression error is actually quite high when flying high and fast.... like 20 kts and higher...)
2. Why does the TAS change pretty significantly (like changing from 150 kts to 140 in a millisecond) when you fly in turbulent areas (or near thunderstorms), but your IAS on your PFD stays pretty the same? - Let's suppose you are on final approach with a VREF of around 140, and it is turbulent. You will see that your IAS only will vary slightly from like 139 to 141, your GS will actually stay almost the same, but your TAS speed goes up to 150, then back to 140, etc. Any explanations?
1. is the IAS on your PFD a CAS or EAS? When reading the FCOM's, I would say it is CAS; however, wouldn't it make more sense that this should be EAS, since EAS is IAS corrected for position AND compression error (and compression error is actually quite high when flying high and fast.... like 20 kts and higher...)
2. Why does the TAS change pretty significantly (like changing from 150 kts to 140 in a millisecond) when you fly in turbulent areas (or near thunderstorms), but your IAS on your PFD stays pretty the same? - Let's suppose you are on final approach with a VREF of around 140, and it is turbulent. You will see that your IAS only will vary slightly from like 139 to 141, your GS will actually stay almost the same, but your TAS speed goes up to 150, then back to 140, etc. Any explanations?
Join Date: May 1999
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As to (1) I agree, but ultimately CAS or EAS is just a measuring system and it depends how limitations (VS, VD etc...) are expressed for that type, the display should match the unit used for limitations. There was a long discussion on Tech Log recently. I think at least one modern jet (Phenom?) uses EAS.
