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. (M)