How does EEC/FADEC recognize/anticipate engine acceleration/deceleration?

Question

So I'm wondering, when the engine runs at idle and the pilot sets a higher thrust level, what exactly happens, that the EEC/FADEC recognizes, that I want to accelerate? My professor said, it's anticipating the upcoming acceleration through:

• $TRA > TRA_{threshold}$
• $pt_3 < pt_{3_{min}}$ (cabin bleed)
• $N2/\sqrt\theta < N2/\sqrt\theta_{idle}$ with $\theta = Tt2/T_{t ref}$

I get that the TRA (throttle lever angle) is higher than my previous one, hence I just raised it. But why exactly would pt_3 be lower than pt3_min, and why is $N2/\sqrt\theta$ smaller than idle? That would indicate that Tt2 has increased.

Answer 1

You probably need to go ask your professor for clarification. But let's look at it this way: what would it mean if $Pt3 > Pt3_{min}$ and $N2/\sqrt{\theta}>N2/\sqrt{\theta}_{idle}$. It means that the engine is probably NOT at idle. So in that situation, if you move the throttle, you probably do want to increase thrust, but not from idle. The EEC may have different control schedules for idle vs above idle operation.