Database: airline
Question: What is the flight number of the flight operated by American Airlines Inc. that had the longest delay in departure?
SQL: SELECT T1.OP_CARRIER_FL_NUM FROM Airlines AS T1 INNER JOIN Airports AS T2 ON T2.Code = T1.ORIGIN INNER JOIN `Air Carriers` AS T3 ON T1.OP_CARRIER_AIRLINE_ID = T3.Code WHERE T3.Description = 'American Airlines Inc.: AA' ORDER BY T1.DEP_TIME DESC LIMIT 1