Delta Air Lines struggled for a fourth straight day to recover from a worldwide technology outage caused by a faulty software update, stranding tens of thousands of passengers and drawing unwanted attention from the federal government. The airline’s chief executive said it would take “another couple days” before “the worst is clearly behind us.” Delta’s chief information officer said Monday that the airline was still trying to fix a vital crew-scheduling program. Other carriers were returning to nearly normal levels of service disruptions, intensifying the glare on Delta’s relatively weaker response to the outage that hit airlines, hospitals and businesses around the world. Transportation Secretary Pete Buttigieg spoke to Delta CEO Ed Bastian on Sunday about the airline’s high number of cancellations since Friday. Buttigieg said his agency had received “hundreds of complaints” about Delta, and he expects the airline to provide hotels and meals for travelers who are delayed and to issue quick refunds to customers who don’t want to be rebooked on a later flight. “No one should be stranded at an airport overnight or stuck on hold for hours waiting to talk to a customer service agent,” Buttigieg said. He vowed to help Delta passengers by enforcing air-travel consumer-protection rules. Bastian said in a video for employees that he told Buttigieg, “You do not need to remind me. I know, because we do our very best, particularly in tough times, taking care of our customers.” Delta has canceled more than 5,500 flights since the outage started early Friday morning, including at least 700 flights canceled on Monday, according to aviation-data provider Cirium. Delta and its regional affiliates accounted for about two-thirds of all cancellations worldwide Monday, including nearly all the ones in the United States. United Airlines was the next-worst performer since the onset of the outage, canceling nearly 1,500 flights. United canceled only 17 Monday flights by late morning, however. Other airlines that were caught up in the first round of groundings also returned mostly to normal operations by Monday. That included American Airlines, Spirit Airlines, Frontier Airlines and Allegiant Air. Bastian, the Delta CEO, said in a message to customers Sunday that the airline was continuing to restore operations that were disrupted. One of the tools Delta uses to track crews was affected and could not process the high number of changes triggered by the outage. “The technology issue occurred on the busiest travel weekend of the summer, with our booked loads exceeding 90%, limiting our re-accommodation capabilities,” Bastian wrote. Loads are the percentage of sold seats on each flight. Airlines have large, layered technology systems, and crew-tracking programs are often among the oldest systems. When the outage began Friday, it also affected systems used to check in passengers and make pre-flight calculations about aircraft weight and balance, airlines reported. United and American reported intermittent problems communicating with crews in the air, contributing to their decisions to briefly ground all flights. Some airlines, including Southwest and Alaska, do not use CrowdStrike, the provider of cybersecurity software whose faulty upgrade to Microsoft Windows triggered the outages. Those carriers saw relatively few cancellations. Delta, however, said that “upward of half” its IT systems are Windows-based. The airline said the outage forced IT employees to manually repair and reboot each affected system and synchronize applications so they start […]