As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 4478 THE CREW REPORTED A BURNING EXHAUST ODOR IN AC PACKS/GASPERS WITH THE SMELL OCCURRING MULTIPLE TIMES DURING DESCENT WITH THE ENGINES AT IDLE. THE AIRCRAFT LANDED AT IAH WITHOUT INCIDENT WHERE MAINTENANCE REMOVED AND REPLACED THE DISTRIBUTION SYSTEM MUFFLER, OPERATIONALLY TESTED WITH NO DEFECTS NOTED AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.