WASHINGTON (Bloomberg) — Southwest Airlines Co., American Airlines and 20 other carriers must pay the US government $219 million in back security fees covering more than two years, a federal agency said.Southwest owes the most, $54 million, followed by AMR Corp.'s American at $40 million and Delta Air Lines Inc. at $32 million, Transportation Security Administration spokeswoman Ellen Howe said yesterday in an interview. The carriers will face penalties if they don't pay or make a plan to do so in 30 days, she said.