MIAMI — Denver-based ultra low-cost carrier Frontier Airlines today announced a deal to acquire nine Airbus A321ceo aircraft. No engine order was included in the announcement. The A321 joins a fleet currently comprised of 20 A320s and 35 A319s, and the carrier has ordered 80 A320neos.

In a letter to employees on November 21, CEO David Siegel said deliveries of the aircraft type would begin starting in late 2015.

“This is an exciting day for our airline as it marks our first ever orders for the largest A320 family member and allows us to continue to grow while keeping costs in check,” he said. “We do know that the order will drive additional hiring for pilots and flight attendants as these aircraft are slated as growth aircraft, not fleet replacement.”

Addison Schonland, a partner at aviation consultancy Airinsight, the Frontier order is consistent with what other airlines have done. “American Airlines converted its A319s to A321, and JetBlue is moving toward A321s,” he said. “Frontier is trying to move into long-haul flights as a way to drive down unit costs.”

The A321 with sharklets has the potential to fly almost coast to coast, said Schonland. “So they may be going with a longer-haul aircraft to do more creative things with their fleet,” he said. “What if they start looking at markets in Mexico, Canada or the Caribbean in a move to go after holiday traffic?”

Siegel called the A321 “a natural fit” with Frontier’s brand of ‘Low Fares, Done Right.’ The aircraft “will continue to help meet our customers’ expectations for a safe and reliable travel experience while allowing us to provide low fare service to more of the country.”