Hello everyone, I would like insight to an observation recently made when flying the ATR 72. Our engines on the frame are the PW124. Usually, when one the automatic temp controller demands bleeds, there is a resulting Torque - Decrease and ITT - increase. This is in case of normal airflow (approx 15psi to the packs). Couple of days ago, we selected Hi flow without changing the Temp knob position (just under 30 PSI now as per the FCOM), we saw an ITT - decrease initially down by 10-20 deg and then very slowly creep up to the original value but not more than that. Can someone share the knowledge on why this would be the case ? we tried this with the temp knob on different settings and the cockpit temp was stabilized.

I am not sure if engine architecture has to do something with it since the PW124 has not axial compressors only 2 Centrifugal ones? That is where my head was going towards not sure if am even in the ball park.

Any help greatly appreciated.

Thanks

What power setting/phase of flight were you at? On the PW12* series the bleed source will swap between P2.5 & P3 and you'll sometimes see ITT decreases as the increased bleed demand at certain torque settings may trigger a swap to P2.5 which is actually less demanding a source than P3. It's a system run by pressure switches and relays so it's not fancy.

Its during cruise and Max cruise power.
Thank you for the that, it kinda makes sense. 2.5 flows more than 3 ? I agree with you on the the pressure switches and check valves.