Originally Posted by
EXDAC
How can the airspeed Indicated on an Air Speed Indicator be anything but Indicated Air Speed? Indicated means exactly that - the speed that is indicated by the indicator. No matter what compensation, calibration, or correction is applied it is still Indicated Air Speed.
Shouldn't the question be - why can't IAS be equal to EAS?
Sometimes etymological origin doesn’t map nicely onto technical usage. In this case, after about a hundred years when indicators have become capable of indicating things unthinkable originally - but the need to keep track of some of the speeds before correction has been applied, has remained, leading to some ambiguity.
If you automatically say that whatever is shown is IAS, then you lose the ability to talk about pre-correction speeds. Like most modern jets that indicate TAS as well as IAS - do we get confused and say oh my God, there’s one IAS and another IAS that differs by 50%? Of course not. We know that of the two speeds that are literally indicated, only the one labelled IAS is the aeronautical definition of IAS.
Back to the original question about EAS, now I’m more siding with Goldenrivett and don’t think that they’re showing us EAS without telling us (like I was suggesting before) as it can be a 20-25 knot difference in cruise, and I think it’s a significant enough difference (hopefully, at least) they wouldn’t sneak it by us.
But I did look at what my manual says, and (not explicitly, but suggestive language) that what is displayed on the PFD is CAS.