What was found
THE A/C FAILED TO PRESSURIZE DURING THE CLIMB PHASE OF THE FLT. THE A/C RETURNED TO THE FIELD AND LANDED, W/O ANY FURTHER PROBLEMS. OUTSTATION MX INSPECTED AND APPROVED THE A/C FOR A FERRY FLIGHT TO CAK MX BASE FOR REPAIR. CAK MX INSPECTED AND TIGHTEND A LINE ON THE PNEUMATIC OUTFLOW VALVE AND CHECKED THE ENG CONTROL LEVER MICROSWITCH RIGGING. OP CHECKS WERE COMPLETED AND THE A/C WAS RETURNED TO SERVICE. LATER IN THE DAY, THE A/C FAILED TO PRESSURIZE INBOUND TO PIT. PIT MX INSPECTED AND REPLACED THE PNEUMATIC OUTFLOW VALVE, IAW DORNIER MM 21-31-03. OS CHECKS WERE COMPLETED, AND THE A/C WAS RETURNED TO SERVICE.