During a recent flight, I used FLCH for a descent. I noticed that the power level came back to about 42%. I thought FLCH should have brought the power back to idle while the aicraft pitch for the selected speed. Any comments?

That is idle for that phase of flight.

Well in air there should be windmilling effect on engine so a full idle should not be possible like a ground idle.

Got it. I guess I was influenced by other add-ons that show about 29% after activating FLCH. Thanks

It brings the thrust back to **flight** idle. The exact thrust setting depends on ambient temperatures and bleed demand (e.g. whether engine anti-ice is on, etc). "Flight idle" is higher than "idle" (or "ground idle"). It ensures there is sufficient bleed air to maintain cabin pressurization, air flow through the core, etc.. If you bring the power back too far you risk a flame out, the pressurization system can't maintain altitude, etc. All this is handled by the EECs. Best regards,Robin.