What was found
DURING CRIUSE AT FL 290, EXPERIENCED A RAPID DECOMPRESSION. THERE WAS A POPPING WOOSH SOUND, FOLLOWED BY CABIN PRESSURE RISING. WENT ON O2 MASKS & BEGAN AN IMMEDIATE EMERGENCY DESCENT TO 10000 FT. ABLE TO DESCEND QUICKLY ENOUGH THAT PAX MASKS DID NOT DEPLOY. NO CAS MESSAGES WERE NOTED OTHER THAN CABIN ALTITUDE CAS WHILE DESCENDING. ATTEMPTED A GROUND PRESSURIZATION WITH APU. RUNNING APU BLEED, DISCOVERED A CRACK IN MIXER ASSEY. FROM ACM. NO OTHER PRESSURE LEAKS. 5-19-2024. REMOVED LEAKING AIR MIXER ASSY P/N 7415724-50. INSTALLED THE NEW AIR MIXER, OPS & LEAK CHKD GOOD IAW AMM 21-20-00, & 21-30-00.