Share: For the second time in four years, the low-cost carrier Frontier Airlines has filed for an initial public offering (IPO). What Happened: The Denver-headquartered airliner was publicly-traded prior its to filing for bankruptcy in 2009. Republic Airways Holdings acquired Frontier for $108.8 million out of bankruptcy, and in 2013 it was sold to the private equity firm Indigo Partners for $145 million. Frontier previously filed an S-1 seeking to raise $700 million in March 2017, but that filing remained dormant before it was withdrawn last summer. The coronavirus pandemic made a significant dent in the airline industry and Frontier was not immune from its tumult. According to its regulatory filing, the company posted a $225 million loss in 2020 on revenue of $1.25 billion, compared with net income of $251 million on sales of $2.5 billion during 2019.