What was found
WHILE CLIMBING THRU APPROXIMATELY 22,000, WE HEARD A SINGLE POP SOUND. THE CABIN RATE SHOWED AN IMMEDIATE RATE OF CLIMB OF AROUND 200 FT MIN & THEN WENT TO DASHES. THE CABIN ALTITUDE STARTED TO CLIMB & PEAKED AROUND 11,000 AFTER WE INITIATED AN EMERGENCY DESCENT TO 10,000. AFTER LEVELING AT 10,000, THE PRESSURIZATION SYS WAS ABLE TO MAINTAIN A CABIN ALT OF 5900 FT. PERFORMED VISUAL INSPECTION OF PACK SYS & FOUND LT RAM AIR CHECK VLV DUCT CRACKED. FOUND GND CONNECTION VLV FLAPPER SEAL MISSING. R & R LT RAM AIR CHECK VLV DUCT IAW AMM 21-25-02. REPLACED GND CONNECTION VLV FLAPPER SEAL IAW AMM 21-22-04. PERFORMED FUNCTION TEST OF CABIN LEAKAGE IAW AMM 21-31-00, NO DEFECTS FOUND.