Originally Posted by
flightleader
Well, if the ground speed didn’t change, the airspeed shouldn’t change much, not that he would have flew into a jet stream at that altitude.
It can change more with altitude than you think, and you don't need much change before you reach the limitations of certain aircraft.
And consider that your ground speed has to increase with altitude to maintain the same indicated/calibrated air speed... some 6 kts per 1000 ft is a "rule of thumb" we use for ease of use when working aircraft.