On the Tent 892....
Minimum Idle is 54.0 according to the Propulsion Dats Limits page on the MAT. This was on the last flight I did. I'll check on the next flight if it changes. Approach idle is not a fixed value but keeps the engines unspooled. To quote from the manual, Approach idle is selected when either
1) Engine Anti-ice is ON
2) Flaps 25 or greater
3) One hyd sys pump ADP is inop with the flaps extended
4) Opposite engine bleed air valve is closed
Please do correct me if I am wrong.
Cheers