What was found
ON DESCENT WITH POWER AT IDLE UNABLE TO MAINTAIN CABIN ALTITUDE. WITH POWER AT IDLE CABIN ALTITUDE CLIMBS AT 1000 + FPM (UP TO 2000' FPM). GROUNDED - YES. PERFORMED FIM TASK 21-31 TASK 801 FAULT CODE 30 "LO ONFL/HI LEAKG" & FC:31 "ACFT RATE HI" TN 83453 10/12/2023. PREFORMED BITE TEST ON PACK/ZONE TEMPERATURE CONTROLLER REF AMM 21-61-00-700-806-002. TEST PASS. PREFORMED AIRPLANE PACK OPERATAION CONFIDENCE CHECK REF AMM 21-00-05-780-801. CABIN LEAKAGE RATE FALLS INTO OPTIMUM LEVEL. TEST GOOD.