"We're really excited about it and getting good feedback," Biffle told Reuters in an interview.
Frontier has been vying with JetBlue Airways Corp to acquire Spirit. Either of the deals would create the fifth-largest U.S. airline.
Denver-based Frontier last week bumped up the cash component of its offer for Spirit by $2 per share to $4.13 per share and agreed to prepay $2.22 per share as a cash dividend to Spirit stockholders following approval of the transaction. It also increased its reverse termination fee to Spirit by $100 million to $350 million.
(Reporting by Rajesh Kumar Singh; Editing by Leslie Adler)