Hello All:

This question is for a real-world pilot or anyone who knows.

I was having a spirited discussion with a real-world pilot friend of mine in which I was explaining to him that I was flying my 767 at FL390 and the IAS was 256 knots, the MACH indicator was .80 and the Groundspeed was 465 knots.

Immediately he launched into a heated argument about the indicated being too low for that high of a groundspeed.

I explained to him that since I've been flying these jets at these high altitudes, the barber pole that indicates the fastest you can fly at any altitude, begins to drop to low airspeeds as you climb higher and higher and in this particular flight, it was anchored at 270 knots.
I'm not sure why this happens, so I was unable to explain to him why.

Question: Can anyone explain why the indicated airspeed at high altitudes are so low while the groundspeeds are so high (in general)?

In this case, my heading was 146 and there was a wind from 203 at 11 knots.

Thanks!

Cyclopian.

Is is all explained here in simple terms

http://www.aerospaceweb.org/question/instruments/q0210.shtml

Even though you indicated that the wind is only 11 knots this would have been taken from the nearest gound weather station.
When you reach high altitudes you encounter winds aloft. These can reach 100 knots easily.

Hope this helps

Dax

Thanks Dax. I appreciate it!

Cyclopian.