As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED AN ELECTRIC/PLASTIC SMELL COMING FROM AFT CABIN VENT ON THE VERGE OF INTENSE. BEGAN OUT OF 15,000 FEET. CREW DECLARED AN EMERGENCY AND RETURNED TO BNA WITHOUT FURTHER INCIDENT. MAINTENANCE DETERMINED THE RIGHT PACK ACM WAS THE SOURCE OF THE SMELL. REPLACED RIGHT PACK ACM IAW AMM 21-51-11. OPS AND LEAK CHECKED SATISFACTORY. NO SMELLS NOTICED DURING PACK RUN. ALSO CHANGED RECIRC FILTERS.