A Frontier Airlines plane near a Spirit Airlines plane at the Fort Lauderdale-Hollywood International Airport on May 16, 2022 in Fort Lauderdale, Florida.Frontier Airlines is going after customers of Spirit Airlines, whose financial footing has gotten so shaky in recent weeks that it warned earlier this month it might not be able to survive another year without more cash.Frontier on Tuesday announced 20 routes it plans to start this winter, many of them in major Spirit markets like its base at Fort Lauderda ...