Redline NG when not expecting it

[KRoy7]

I was trying to find the root cause of an alarm in cruise flight (see picture), and had to pull the TQ back below 1000 ft-lb and then the alarm went off. Would appreciate guidance on where my root cause might be, I followed each of the checklists along the way.

Thanks ...

[Orlaam]

Looks like you are overspeeding. Redline is 200 knots.

[Black Square]

Exactly :)

I suspect you're not the only one to do this, because I've heard an improbably high number of users complaining about a "CO2 alarm" in cruise in the turbine aircraft within 24 hours of the aircraft releasing.

[KRoy7]

@Black-Square So the turbine Duke's speeds (below) are much higher, I understand they are True Airspeeds, not indicated airspeed. But obviously I did not consider that. Ok, this is great education. The checklist values clearly would be variable as well based on density altitude I suppose.

Aircraft Performance (Turbine Duke)
Maximum Cruising Speed 320 ktas
Normal Cruising Speed 290 ktas
Economy Cruising Speed 225 ktas

Appreciate the feedback! Kirk