Among the flights of the air carrier described as American Airlines, what is the percentage of the flights with earlier departure?
American Airlines can be found in Description which contains 'American Airlines'; percentage = MULTIPLY(DIVIDE(SUM(DEP_DELAY < 0), COUNT(DEP_DELAY)), 1.0); earlier departure refers to DEP_DELAY < 0;
SELECT CAST(SUM(CASE WHEN T2.DEP_DELAY < 0 THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM `Air Carriers` AS T1 INNER JOIN Airlines AS T2 ON T1.Code = T2.OP_CARRIER_AIRLINE_ID WHERE T1.Description LIKE '%American Airlines%'