What is the flight number of the flight operated by American Airlines Inc. that had the longest delay in departure?
flight numbers refers to OP_CARRIER_FL_NUM; American Airlines Inc. refers to Description = 'American Airlines Inc.: AA'; longest delay in departure refers to MAX(DEP_DELAY);
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