Three Facts About Allegiant Air that you probably didn't know about Allegiant Air flies less frequently compared to other U.S. airlines. To maintain low fares, Allegiant decided to only offer flights to most destinations only a few times a week compared to everyday service. Allegiant Air is the sole year-round air carrier operating at Phoenix-Mesa Gateway Airport. The airline offers more flights out of this airport compared to the more popular Phoenix Sky Harbor International Airport, consistent