A Dec. 21 internal memo circulated at Southwest Airlines hinted at what would become the company’s cataclysmic meltdown just days ahead of Christmas, accounting for some 90% of the flights cancelled by U.S. carriers, according to FlightAware. According to the memo, the company was well aware of significant staff shortages at some of its major hubs, including Denver, where ramp workers were calling out sick en masse. The alert was severe enough for the company to issue a “state of operational emergency,” according to The Washington Post, cornering workers into choosing mandatory overtime or to face the prospect of being let go if they failed to provide a doctor’s note. The scheduling catastrophe stranded thousands of flyers as a record bitter cold blasted the country. Southwest is currently being investigated by the Department of Transportation as well as by the Senate Commerce Committee over the fiasco. In a public statement issued on Tuesday, CEO Bob Jordan said the company plans to fly a reduced passenger schedule to get it back on track “before next week.”