As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5685 - EWR - FLIGHT CREW REPORTED BURNING PLASTIC SMELL IN CABIN DURING CLIMBING. CREW PERFORMED AIR RETURN AND LANDED ACFT UNEVENTFULLY. IAD MX PERFORMED ENGINE RUNS AND RAN SYSTEMS AND FOUND NO DEFECTS, EVALUATION FLIGHT WAS PERFORMED AND NO DEFECTS FOUND. ACFT WAS APPROVED TO RETURN TO SERVICE.