— Frontier Airlines officials on Thursday said the company would begin flying passengers to six new destinations from Raleigh-Durham International Airport.

The new routes adds to the 49 nonstop destinations that the airport already offers. Frontier itself flies more than 1,500 routes to 89 different destinations across the country, officials said at a news conference.

The new flights from RDU will go to Buffalo, Houston, Milwaukee, New Orleans, San Antonio and San Juan, Puerto Rico. The additional flights bring Frontier's number of destinations from RDU to 15.

RDU transported 11.6 million passengers in 2017, about 32,000 people per day. The airport said it has an $8.5 billion regional economic impact that supports 5,000 jobs on its Morrisville campus.

This is the second time in less than a year that Frontier has announced an expansion.

Last July, the carrier announced that it was doubling in size by adding 21 new cities and 85 new routes to the airline's network. By the summer of 2018, Frontier was expected to operate 314 non-stop flights throughout its network.

Over the last decade, Frontier has been transformed from a bankrupt legacy carrier into a rapidly expanding, ultra-low cost airline under new management.

The Denver-based airline filed for an IPO in March and is eager to show its growth potential to investors.

The number of passengers flown by Frontier grew by more than 15% last year and its planes were more full than any carrier, according to the Bureau of Transportation Statistics.

Its aggressive expansion is aimed at established carriers like Southwest Airlines and United Airlines. For example, Frontier's new routes will make it the airline with the second most destinations from cities like Orlando, behind Southwest.

RDU has also seen robust growth from other airlines.

Last year, five airlines added flights from RDU to Paris, New Orleans and Austin, Texas.

And last March, Virgin American became the airport's 10th carrier when it launched service to San Francisco.