What was found
FLIGHT 4435, CREW REPORTED A BURNING ODOR IN THE COCKPIT TWICE DURING FLIGHT. THE CREW SMELLED IT IN THE COCKPIT AND CABIN AND THE ODOR LASTED APPROX ONE MINUTE EACH TIME THEN DISSIPATED. SMELLED ELECTRICAL. COM 1 WAS REPLACED IN RDU. AIRCRAFT REMOVED FROM SERVICE. PERFORMED FIM TASK 21-20-00-810-801-A. NO SOURCE FOUND. FUNCTIONAL CHECK FLIGHT FOUND TO BE SATISFACTORY. COMPLIED WITH AIRWORTHINESS RELEASE SIGN-OFF. NO SOURCE FOUND OF ODOR FOUND. AIRCRAFT RETURNED TO SERVICE.