Just curious, does the PT6 engine you're describing use P3 bleed air to modulate the fuel supplied fuel control unit? Or are the power levers directly connected to the the fuel metering?
Each power lever is mechanically connected to its respective fuel control unit and the primary governor. Bleed air does not participate in fuel metering.
Jimmy Little asked
Can the engine controller on something like the PT6 automatically detect the conditions caused by the stuck-open bleed valve and issue the appropriate warning? It would seem relatively easy to correlate fuel consumption, temperature, and such to detect this, or at least warn that it's an issue.
I need to point out that this is not a computer-controlled engine. It predates the invention of the microprocessor. So yes, there is temperature detection and yes, correlation between high NG, high T5 and torque lower than selected by the power levers might well indicate a stuck open bleed air valve, but this information isn't digitised. The computer that correlates the data is the pilot's brain, hence the need for all this training. (Not to say that the folks flying the computerized airplanes don't need training: they need to know "what it's doing now.")