What was found
HAD TO BE AT 21000 FEET TO HOLD CABIN PRESSURE OF 10000 FEET WITH OVERBOARD VALVE OPEN. ON INBOUND, FOUND OVERBOARD EXHAUST VALVE FULLY OPENED, NOT PARTIALLY OPENED IAW MEL 21-23-06 FIG 21-23-06 B, CAUSING ELBOW DUCT ABOVE OVERBOARD EXHAUST VALVE TO COLLAPSE AND CRACK OPEN THE DUCT. REMOVED AND REPLACED ELBOW DUCT ASSY AT THE OVERBOARD EXTRACT VALVE ASSY. IAW SMP. OK FOR SERVICE.