As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT AIR RETURNED TO SAL ON ACCOUNT OF LOSS OF BOTH PRESSURIZATION SYSTEMS. MAINTENANCE REPLACED OUT FLOW VALVE (10HL) IAW AMM 21-31-51-400-001-A AND PERFORMED TEST THE PRESSURE CONTROL AND MONITORING SYSTEM IAW AMM 21-31-00-710-002-A.