Just a question to the avionic guys here:
We are about to configure my new Aspen PFD.
In the configuration menu, there is the item IAS Unit, which can be mph or kt.
Question: Does the selection of this unit influence the display of TAS / Windspeed or is TAS / Windspeed always in Knots? Or can it be configured to be in kts while IAS is in mph?
As the ASI in my plane has both scales, we can do both, we’d have to simply add the converted speed figures to the AFM Supplement. As it has been operated under mph so far, I would not mind having IAS as mph, but I absolutely do not want wind and TAS as mph, but as kts.
Has anyone an idea about this? I know my avionics people will, but I wanted to fill in the forms over the weekend and I missed this little detail.
Many thanks.
The windspeed is in the same unit as the air speed is.
Thanks, that is what I feared.
Actually that is a tricky issue, given that wind is always passed by ATC as knots, why do some planes have ASIs marked in mph or even km/h?
I know Marketing loves mph and even more loves km/h…
It’s just the way they indicated airspeed until the mid seventies. Cessna switched from mph to knots between the 1975 and 1976 model years I believe. Piper very much in the same time, maybe in 1977. Don’t know if wind was measured, reported and read out in miles per hour before that.
wind is always passed by ATC as knots
in certain parts of the world…
METARs from eastern Europe still give wind speed in m/s, I do not know what units ATC uses there but I can only expect m/s too.
But I agree that mph is useless, today.
Peter, ‘nobody’ in US GA knew what a knot was until the 70s. Although its probably too late now, I think changing to knots ended up being the wrong move. GPS makes the navigational significance of a nautical mile almost irrelevant, and distances in the ground are better known to pilots and others in ‘real’ miles.
A friend flies his Bücker with the original km/hr ASI and has a three way conversion problem for planning and reporting, every day units to Bücker units to ATC units.
(I have one plane/ASI in each of Knots and MPH, and obviously prefer MPH)
BTW my own plane was bought from Hungary, it has the ASI in km/h, altimeter in metres and vario in m/s. One gets used to converting. Gliders here have the ASI in km/h, too.
@Silvaire: miles, “real” or not, are a thing of the past anyway. Your country, influential though it may be, is about the last in the world to cling to miles, feet, and inches. I hear that even in the US, homebuilders commonly have both Imperial and decimal measuring equipment.
Distances on the ground are known in kilometres.
But frankly, I have no issue living with two systems of unit. Three is one too much, though.
I’m searching for a JPEG of the French revolutionary period watch with 10 hrs/day 
