 Air travel issues continued through the weekend as the airlines worked to restore systems that crashed. After a flawed software update pushed out by CrowdStrike, the outage impacted a range of businesses from airlines to hospitals to banking and mobile ordering at Starbucks. And Delta Airlines is apologizing for the thousands of flights it canceled as many of its systems failed. Data from the aviation analytics firm Serium showed that Delta stood out as the airline that took the biggest hit from the tech meltdown.