What was found
(CAN) DURING CRUISE, FLT LEVEL 370, UNUSUAL CABIN ALTITUDE IN AUTO SYSTEM 2 OF 6,500 FEET. SAFETY VALVE OPENED TWICE FOR A BRIEF PERIOD, APPROXIMATELY 2 MINUTES LATER, CABIN DEPRESSURIZED AND EMERGENCY DESCENT CARRIED OUT. CONTROL REGAINED IN MANUAL MODE AT FLT. LEVEL 200. OUTFLOW VALVE REPLACED. SYSTEMS 1 AND 2 TESTED SERVICEABLE.