UNITED STATES SECURITIES AND EXCHANGE COMMISSION (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2021 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-35186 _______________________________________________________________________ SPIRIT AIRLINES, INC. (Exact name of registrant as specified in its charter) _________ ...