What was found
AIRCRAFT NOT GROUNDED-DURING CRUISE FLIGHT, AT FL 370-50 DEG SAT, THE PRESSURIZATION OUTFLOW VALVE INDICATED A SUDDEN MOVE TO FULL OPEN THEN CLOSED, RESULTING IN 1000 FPM LIMIT THEN DESCENT OF CABIN PRESSURE. MEL 09-499C-C ONE CABIN AUTO PRESSURE CONTROL, REF. 2110A AUTHORIZED. REPLACED CABIN PRESSURE CONTROLLER NR 2, PER AMM 21-31-01, DCPC (DIGITAL CABIN PRESSURE CONTROLLER) SYSTEM TEST OKAY, CLEARED MEL.