Frontier Airlines (F9, Denver International) retired its last A319-100 on September 8, 2021, thereby transitioning its entire fleet to larger Airbus narrowbody variants.

N949FR (msn 2857) operated its last revenue flight from Nashville International to Denver International and was subsequently ferried to Tampa International on September 8. The aircraft is 15.1 years of age and was operated by Frontier Airlines since new.

The airline operated a total of fifty-two A319-100s, although never more than 49 at a time, the ch-aviation fleets history module shows. The type's fleet peaked in 2008 and has been gradually decreasing since then. Each of Frontier's A319s seated up to 150 passengers in a single-class layout.

Following the retirement of its smallest type, the American low-cost carrier continues to operate nineteen A320-200s, seventy-one A320-200Ns, and twenty-one A321-200s. It has a further sixty A320-200Ns, sixty-seven A321-200Ns, and eighteen A321-200NY(XLR)s on firm order from Airbus. It recently announced commitments for a further ten A321-200Ns from undisclosed lessors.