Delta and United Airlines topped the list. Delta Chief Executive Ed Bastian said in a message to customers Sunday that flight cancellations continued as the airline tried to recover its systems and restore operations. He noted that the pause in Delta's operations resulted in more than 3,500 Delta and Delta Connection scrubbed flights. Delta has been offering waivers to affected customers. Bastian noted that that one of their crew tracking-related tools was affected and unable to effectively process the unprecedented number of changes triggered by the system outage.