Spirit Airlines is offering an 85% discount on certain flights for one day only. All tickets must be booked by 11:59 pm on Wednesday, May 2. The fare sale covers travel between May 9 and June 13 as well as September 5 and October 31, 2018. The Florida-based ultra-low-cost carrier is offering the 85% discount to celebrate is 85% on-time performance rating in March. The discount doesn't cover the passenger usage charge, regulatory compliance charge, and fuel charge.