What are the names of the top 5 airlines with the highest number of aircraft?
names of the airlines refers to Description; highest number of aircraft refers to MAX(COUNT(TAIL_NUM));
SELECT T2.Description FROM Airlines AS T1 INNER JOIN `Air Carriers` AS T2 ON T1.OP_CARRIER_AIRLINE_ID = T2.Code GROUP BY T2.Description ORDER BY T1.TAIL_NUM DESC LIMIT 5