What was found
THE CREW REPORTED A RAPID DEPRESSURIZATION (>3000FPM) WHILE CLIMBING THROUGH 21,000' AND THAT THEY COULD NOT RECOVER PRESSURIZATION. THE CREW PERFORMED AN EMERGENCY DECENT AND LEVELED OFF AT 10,000'. THE ACFT RETURNED TO DEPARTURE WHERE IT LANDED WITHOUT INCIDENT. MX INSPECTED THE ACFT, FOUND SEAL ON CARGO DOOR LOWER SIDE HAD COME OFF. MX REINSTALLED THE DOOR SEAL, OPERATIONALLY CHECKED PRESSURIZATION AND LEAK CHECKED CARGO DOOR ALL WITH NO DEFECTS NOTED, AND THE ACFT WAS APPROVED FOR RETURN TO SERVICE.