This is very confidently stated, but very incorrect. Even though it’s slightly off topic (but not really, as it demonstrates a broader misunderstanding of how weather affects aircraft and resultant expectations of sim weather), in the interest of not allowing this fallacy to be spread as fact, I’m going to explain:
Your POV with regard to IAS increasing on the ground is happening because in that case the aircraft is at a fixed reference point on the ground and the fluid of the air is moving around it, thus changing the IAS. However, once airborne, the airplane becomes part of the fluid and changes in the speed of the fluid itself only affect the resulting groundspeed.
Yours is a common misconception that leads to dangerous fallacies like believing the airplane encounters a change in performance when turning from the upwind to the downwind in the pattern, or when doing a 360° turn. It does not. In fact, you could do a rapid turn of several degrees per second, essentially moving the relativewind yourself, and your airplane’s performance will not change (the only limiting factors being wing loading in the turn and available excess power), only your groundspeed and ground track will. Try this in a series of sustained, stabilized 360° turns and you will see the performance remain the same throughout.
An airborne airplane simply does not care (performance-wise) which way the wind is moving over a fixed reference point as measured on the ground.
The only exception to this is when there are sudden, drastic changes in the fluid (like with windshear or strong gusts - we’re talking a magnitude of 15kts or more in less than a second), which can momentarily affect indicated speed and performance. However, a positively stable aircraft will quickly regain its original indicated airspeed without any changes in pitch or power, especially in higher-energy regimes of flight.
The only time these sudden, drastic changes in the fluid of the air become problematic is when the aircraft is at a low, draggy energy state (such as final approach or just after takeoff) and the margin above stall speed is thin and/or the resultant momentary change in performance with a sudden, drastic headwind loss is enough to possibly cause contact with the ground or obstacles. This is why we approach at a higher IAS (gust factor) when it’s gusty.
Otherwise, with the vast majority of wind shifts, the IAS will not change.
