Originally Posted by catiamonkey
That's going to create a ton of low speed rejects. Let's say you're going at 40 kts and a 10 kt headwind comes along. Now, according to the model, airspeed is 25% off. The plane shows 55% more drag than I expect. Is it because of a dragging brake? Wing problem? Wind? Not to mention the dynamic change in engine performance. The NASA system commanded a reject at 15% discrepancy, so you'd be stopped by now.
A headwind would generate an increase in airspeed, so if the system used airspeed it would show an increase in performance. But these are technical issues that can be solved by proper design, not reasons to not bother designing it at all.