What was found
(CAN) IN CRUISE AT AN ALTITUDE IN EXCESS OF FL 40 AFTER ALTITUDE CHANGES DOWN AND UP IN EXCESS OF 1000 FEET THE PRESSURIZATION CONTROLLER FAILED TO MAINTAIN CABIN PRESSURIZATION. AN EMERGENCY DESCENT WAS INITIATED AND PASSENGER OXYGEN MASKS DEPLOYED. THE PRESSURIZATION CONTROL WAS ABLE TO BE RESET PRIOR TO LANDING. INVESTIGATION FOUND THAT THIS WAS A KNOWN PROBLEM WITH THIS AIRCRAFT AND WAS ADDRESSED BY AD WIRE 21-004. MFG HAS JUST LATELY RELEASED S/B 45-21-13 WHICH HAS BEEN INSTALLED IN THIS AIRCRAFT AND CONFIRMED TO HAVE CORRECTED THIS PROBLEM.