The US Department of Transportation has launched an investigation into Delta Air Lines, scrutinizing the airline’s slow recovery from a global technology outage that began last week. The investigation will examine whether Delta’s response to the crisis, which has left hundreds of thousands of passengers stranded, violated federal regulations.

The investigation comes as Delta continues to struggle to restore normal operations, days after other airlines have largely recovered from the outage caused by a faulty software update from cybersecurity firm CrowdStrike. While most airlines saw cancellations return to normal levels by the weekend, Delta has canceled over 6,500 flights since Friday, far exceeding any other carrier.

Transportation Secretary Pete Buttigieg expressed concern over Delta’s prolonged disruption, stating, “It’s unacceptable that days after other airlines are back to normal, Delta is still canceling hundreds of flights.” The investigation will also delve into Delta’s customer service practices, including reports of lengthy wait times and stranded unaccompanied minors.

Delta maintains that it is cooperating with the investigation and is working tirelessly to restore operations. The airline attributes the disruption to a reliance on Microsoft Windows systems, including a crucial crew scheduling tool that was overwhelmed by the outage.

However, critics point to Delta’s slow recovery as a sign of systemic issues, highlighting the airline’s reliance on a single technology provider and its apparent lack of contingency plans. They draw parallels to Southwest Airlines’ meltdown in December 2022, where the airline faced similar criticism for its slow response to a winter storm.

The investigation is likely to focus on Delta’s compliance with federal regulations regarding passenger refunds for canceled or significantly delayed flights. The airline has been criticized for offering only eCredits for canceled flights, rather than prompt refunds in the original form of payment.

Sen. Maria Cantwell, chair of the Senate committee overseeing airlines, has expressed concern that Delta is failing to meet passenger rights outlined in a recent law. She has written to Delta CEO Ed Bastian, demanding answers about the airline’s response to the crisis.

The investigation into Delta’s handling of the tech outage is a significant development, raising questions about the airline’s preparedness and its commitment to passenger welfare. The outcome of the investigation could have far-reaching implications for the airline industry, potentially leading to stricter regulations and increased scrutiny of airline responses to future disruptions.