On August 2018, which day had the highest number of cancelled flights due to the most serious reasons in Dallas/Fort Worth International?
On August 2018 refers to FL_DATE like '2018/8%'; day with the highest number of cancelled flights refers to MAX(COUNT(FL_DATE WHERE CANCELLED = 1)); cancelled due to the most serious reasons refers to CANCELLATION_CODE = 'A'; in Dallas/Fort Worth International refers to Description = 'Dallas/Fort Worth, TX: Dallas/Fort Worth International';
SELECT T2.FL_DATE FROM Airports AS T1 INNER JOIN Airlines AS T2 ON T1.Code = T2.ORIGIN WHERE T2.FL_DATE LIKE '2018/8%' AND T1.Description = 'Dallas/Fort Worth, TX: Dallas/Fort Worth International' AND T2.ORIGIN = 'DFW' AND T2.CANCELLED = 1 AND T2.CANCELLATION_CODE = 'A' GROUP BY T2.FL_DATE ORDER BY COUNT(T2.FL_DATE) DESC LIMIT 1