What was found
AIRCRAFT N189PP, LEAR 45 S/N 264, DEPARTED FROM KRIC ON DECEMBER 13 AT APPROXIMATELY 4:00 PM EASTERN STANDARD TIME. SHORTLY AFTER REACHING CRUISE ALTITUDE OF 40,000 FEET THERE WAS A LOUD POP FOLLOWED BY A SUDDEN LOSS OF PRESSURIZATION. AN EMERGENCY WAS DECLARED, AND A RAPID DECENT WAS MADE TO 15,000 FEET. THE AIRCRAFT RETURNED TO KRIC AND MADE A NORMAL LANDING. DURING TROUBLESHOOTING OF THE SYSTEM IT WAS DISCOVERED THAT THE CABIN PRESSURIZATION MUFFLER P/N 12945-096-801 HAD RUPTURED PURGING BLEED AIR INTO THE TAILCONE INSTEAD OF THE CABIN. THIS EXPLAINS THE LOUD POP THE CREW HEARD FOLLOWED BY A RAPID LOSS OF PRESSURIZATION.