US airports are at a breaking point after a ground stop left an estimated 1.5 million people stranded. Travelers are facing cancellations, long lines, and packed terminals as airlines work to rebook passengers. The disruption spans multiple hubs and is compounding an already busy travel weekend. Passengers are being urged to check their airline apps and remain patient as operations slowly recover. The scale of the backlog has raised fresh questions about how the system handles sudden shutdowns.