The shares traded at $11.46, or 4.5 percent below the $12 initial public offering price. Earlier in the session, they had fallen to $11.11.

Miramar, Florida-based Spirit, which specializes in low-priced flights to Latin America and the Caribbean, had priced its offering of 15.6 million shares at $12 apiece, compared with an original target of $12 to $13.

The company raised $187.2 million from its IPO, nearly 42 percent less than it had first expected. Spirit said in a statement Thursday that it expected proceeds of about $171 million after deducting underwriting discounts and other items.

The company, which calls itself an "ultra low-cost" carrier, operates more than 150 flights a day, but carries less than 1 percent of U.S. air passenger traffic.

The airline began operations in 1980 as Charter One, a Detroit-based charter tour operator that provided travel packages to entertainment destinations. In 1992, it changed its name to Spirit Airlines and began offering flights from Detroit to Atlantic City.

The carrier added new cities in the 1990s and Latin American destinations in 2001. It now serves more than 40 destinations.

Spirit Airlines pilots, represented by the Air Line Pilots Association, staged a six-day strike in June 2010 after mediated talks failed to bridge differences with management over pay, scheduling and benefits.

That strike was the first notable job action at a U.S. passenger airline since Northwest Airlines mechanics walked off the job in 2005. Northwest is now a part of Delta Air Lines.

The offering reduces the stake of private equity firms Indigo Partners and Oaktree Capital Management to 72 percent. Such firms buy companies with the aim of exiting their investments a few years later with a large profit.

Citigroup Global Markets and Morgan Stanley were lead underwriters for the offering.