RELATED: Scheduling mix-up could affect American flights over holidays
On Wednesday, the Union representing American Airlines said the airline had informed them of a problem with the pilot vacation system that caused the scheduling snafu.
According to a post on the Union's website, "On Friday, management disclosed a failure within the pilot schedule bidding system. As a result, thousands of flights currently do not have pilots assigned to fly them during the upcoming critical holiday period.
American Airlines has been responding to tweets from many people concerned with their upcoming flights, and is trying to assure fliers they "expect to avoid any cancellations."