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 Lauderdale International Airport in Florida. Frontier overlaps with Spirit on 35% of its capacity, more than any other airline, according to a Monday note from Deutsche Bank airline analyst Michael Linenberg.