Only 58 % of United Airlines flights were on - time in September . Weather is the most common cause of delays for carriers . Fuel disputes and maintenance issues contributed to the steep rate drop . Overall , the airlines ' on - time rates improved over August , but dropped from August 2011 .
Only 58 % of United Airlines flights were on - time in September . Fuel disputes and maintenance issues contributed to the steep rate drop . Overall , the airlines ' on - time rates improved over August , but dropped from August 2011 .