Reports that the owners of Frontier Airlines have been preparing to take the Denver-based airline public have circulated for more than a year. Now, a fresh report suggests they could make the move in the next few months.

Bloomberg said late Tuesday that Phoenix-based private-equity firm Indigo Partners LLC, the airline’s owner, could launch an initial public offering for Frontier as early as the second quarter.

The news service cited unnamed “people with knowledge of the matter” in its report.

It…