 Delta, United, and American Airlines temporarily grounding all flights, regardless of their destination. It is just unclear, just, that's it, unclear, how long this grounding is going to last. Frontier Airlines grounded their flights yesterday because of a Microsoft outage. Those flights have since resumed. Other U.S. airlines also reporting difficulties, including with booking, check-in, and other online functions. Some international airlines, including Qantas and Virgin Australia, also being affected.