What was found
AT 25,000' CRUISE THE ACFT SUDDENLY DEPRESSURIZED. CABIN ALTITUDE INDICATED 25,000', WHITE ALT & RED CAB ALT LIGHTS ILLUMINATED. PAX OXYGEN MASKS DEPLOYED, LIGHT ILLUMINATED & WARNING HORN SOUNDED. ACFT LANDED SAFELY. R & R THE CABIN PRESSURIZATION CONTROLLER & SECURED THE PAX OXYGEN MASKS. A SUCCESSFUL SYS OPERATIONAL CHECK WAS PERFORMED. ACFT WAS RETURNED TO SERVICE.