You won’t redline the ITT when sitting on the ground for a long time, I don’t know where you got that from. A turbine engine quickly reaches operating temperature when applying power and its not relying on airspeed for cooling the same way cylinders on a piston engine are being cooled.
The inertial separator restricts airflow into the engine which causes a loss in performance. In order to regain the lost performance more fuel needs to be burned in the combustion chamber, therefore fuel consumption and ITT increases. So saying that there isn’t sufficient air available for cooling isn’t entirely correct. Basically the effect is similar to having a higher density altitude.
Furthermore this has not much to do with being on the ground or in the air, the engine will receive a bit of ram rise when accelerating but the overall effect is minor, especially on the PT-6A with a reverse flow design. On a straight flow design the effect of ram rise is more pronounced but still doesn’t exceed maybe 5 to 10% torque and a few degrees in ITT depending on engine type during take-off.
Nothing to worry about when flying the TBM930 anyway since that engine is flat rated to an insane temperature, you won’t have to worry about redlining the ITT, inertial separator or not, unless taking off somewhere really hot and high.
I’m not aware of any speed limit with the inertial separator engaged?
On a StreamDeck Profile I made I could use the L:XMLVAR_InertSep (or the like, on vacation and not on pc atm) and it would set the switch, corresponding to 0 or 1 sent to it. With SU5 it seems the XMLvars from MS/Asobo cannot be adressed anymore. At least my Profile has stopped functioning.
I’ll look into this when I come back. This is a major bummer to me as well for the 208 as I hate fiddling around in the cockpit with a mouse. But it seems Asobo has its priorities straight on that interaction method and people with buttons/ homeports are an afterthought.
And it seems they are right with that assumption, as no-one cared to vote on the topic I posted on it.