https://www.fool.com/investing/2017/07/18/was-spirit-airlines-investor-update-good-news-bad.aspx

Heres the paragraph discussing it.....

"Spirit Airlines' poor June operational performance indicates that the pilots have been right to say that the carrier is understaffed. Operational performance may improve in the fall, when aircraft utilization tends to decline seasonally. However, before the 2018 peak season, Spirit Airlines absolutely must increase staffing and mend fences with its pilots, in order to keep flight cancellations under control."