As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 7509 IAD TO ROC ON DESCENT THE CREW SMELLED A BURNING ODOR. FLIGHT ATTENDANTS CONFIRMED A BURNING ODOR IN THE CABIN. CREW SHUT OFF THE RECIRCULATION FANS AND DECLARED AN EMERGENCY. SHORTLY AFTER THE RECIRCULATION FANS WERE SHUT OFF THE SMELL WENT AWAY FOLLOWED BY A -PACK 2 FAIL- EICAS MESSAGE A SHORT TIME LATER. CREW RAN THE QRH PROCEDURE AND TURNED THE NR 2 PACK OFF. FLIGHT LANDED UNEVENTFULLY. MAINTENANCE REPLACED THE NR 2 PACK ACM AND HEAT EXCHANGER.