Question: Among the flights of the air carrier described as American Airlines, what is the percentage of the flights with earlier departure?
SQL: 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%'