 Eastern Time, their grounding comes after a significant Microsoft outage brought Frontier Airlines to a standstill for hours on Thursday, though the ground stop for those airlines has since been lifted. Earlier Thursday, Frontier said its systems had been impacted by the outage and offered refunds for inconvenienced passengers. Other competitors, including Allegiant, Sun Country, also said they were having difficulties, including with their booking, check-in, and trip-managing facilities.