As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 5273 - MCO - DURING LEVEL FLIGHT AT FL180, THE CREW REPORTED A LOUD POP FOLLOWED BY A LOSS OF CABIN PRESSURE. MAINTENANCE FOUND A CHECK VALVE DAMAGED. CHECK VALVE AND DUCT VALVE WAS INSTALLED IN WERE REMOVED AND REPLACED IAW ATR MM. OPS CHECK WAS GOOD AND AIRCRAFT WAS RETURNED TO SERVICE. REF SIMA200116704. (M)