As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL 240, WHEN POWER REDUCED TO IDLE, CABIN LOSES PRESSURE. CABIN CLIMBS AT 1000 FPM. UNABLE TO CONTROL CABIN PRESSURE WITHOUT ADDING ENGINE POWER. ACFT GROUNDED. PERFORMED CABIN PRESSURE LEAK TEST, LEAK CHECK SATISFACTORY IAW AMM 05-51-91. ACCOMPLISHED FIM 21-00-807. AIRPLANE CANNOT MAINTAIN CABIN PRESSURE ON A SINGLE PACK WITHIN SPECIFIED LIMITS. BOTH PACKS OPERATED NORMALLY DURING SINGLE PACK OPERATION. NO DISCREPANCIES NOTED.